Past Events

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Dr. Daniel Dar Department of Plant and Environmental Sciences

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A plant’s roots serve as a major line of defense against environmental stress to protect the plant as a whole. Roots of diverse plant species have found ways to deal with stress by devising responses, often within individual cell types, to resist drought, flooding, mineral deficiencies and other insults that impair plant growth. I will present my lab’s research that uses systems, synthetic and developmental biology approaches to interrogate the transcriptional networks that function in response to many of these environmental stresses in tomato and sorghum.

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University of California, Davis

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California Institute of Technology USA

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Rubisco is the enzyme that catalyzes the first step of carbon sequestration during photosynthesis. Despite the massive flux of CO2 passing through this active site over billions of years, it remains a primary rate-limiting step due to its relatively slow kinetics. We have developed an E. coli strain that couples doubling rate to rubisco biochemical parameters. Using this strain we have characterized all possible point mutations of a model bacterial rubisco (~9000 mutants). This deep mutational scan has allowed us to search for faster rubiscos in high throughput.

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NIH K99 Fellow, Savage Lab, UC Berkeley

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Freiburg University

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Host: Dr. David Zeevi

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Ben Gurion University of the Negev

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Monash University, Australia

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Faculty of Life Sciences, Tel-Aviv University

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ARO Volcani

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University of Auckland

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Segev Lab

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Department of Life Sciences, Ben Gurion University of the Negev

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School of Molecular Cell Biology and Biotechnology, Tel-Aviv University

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Prof. Asaph Aharoni & Dr. David Zeevi Dept. of Plant and Environmental Sciences Weizmann Institute of Science

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University of Haifa

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Princeton University

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Michigan State University

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Abstract: Plants synthesize an amazing diversity of volatile organic compounds (VOCs) that facilitate interactions with their environment, ranging from attracting pollinators and seed dispersers to protecting themselves from pathogens, parasites, and herbivores. Plants are also targets of released compounds as a part of plant-plant communication, as well as plant-insect and plant-microbe interactions. They are constantly exposed to atmospheric VOCs and can differentiate and respond to specific cues. Therefore, VOC release out of the cell and perception of emitted volatiles are an essential part of information exchange. The presented results will cover different aspects of VOC biosynthesis and emission including the involvement of heterodimeric enzymes in VOC biosynthesis, the role of transporters, lipid transfer proteins and lipid droplets in VOC trafficking out o! f the cell, and the function of the cuticle as an integral member of the overall VOC biosynthetic network. This presentation will also discuss the latest knowledge about VOC perception: from an inter-organ aerial transport of VOCs via natural fumigation and hormone-like function for terpenoid compounds to a signaling pathway(s) involved.

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Purdue University, West Lafayette, IN, USA

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Reactive oxygen species (ROS) play a key role in systemic cell to cell signaling which is required for plant acclimation to different stresses, essential for the survival of plants. We recently developed a method to image real-time whole-plant accumulation of ROS and other systemic signals, and together with transcriptomic analysis and physiological measurements, we revealed the involvement of important signaling components in response to localized high light stress leading to systemic acquired acclimation (SAA) in Arabidopsis thaliana. The signal initiation and propagation maintenance are dependent on generation of ROS by RESPIRATORY BURST OXIDASE HOMOLOGS (RBOHs) in the apoplast and transport through the plasmodesmata, under the control of PLASMODESMATA LOCALIZED PROTEIN 1 (PDLP1) and PDLP5. Furthermore, we showed that phytochrome B acts in the same regulatory module as RBOHD and that it can regulate ROS production even if it is restricted to the cytosol. Additional proteins we discovered to function in the maintenance of the signal propagation, are aquaporin PLASMA INTRINSIC PROTEIN 2;1 (PIP2;1), that transport H2O2 across the plasma membrane and calcium channels including GLUTAMATE LIKE RECEPTORS 3.3 and 3.6 (GLR3.3 & GLR3.6), MECHANOSENSORS LIKE PROTEINS 2 and 3 (MSL2 & MSL3). Based on mutants and grafting experiments we identified the role of the ROS receptor HYDROGEN PEROXIDE INDUCED CALCIUM INCREASE 1 (HPCA1) in ROS cell to cell signal propagation, as well as the calcium signal propagation. We also reported that CALCINEURIN B-LIKE CALCIUM SENSOR 4 (CBL4), CBL4 INTERACTING PROTEIN KINASE 26 (CIPK26) and OPEN STOMATA 1 (OST1) are required for the cell-to-cell ROS signals. Altogether, screening more than 120 mutants, we shed light on the underling molecular mechanisms that coordinate the systemic cell to cell signals required for plant acclimation to stress. While most of our work focused on Arabidopsis, we were able to show the ROS auto propagation systemic signals are conserved in evolution and occur also in unicellular algae colonies, non-vascular plants and even mammalian cells. Thus, emphasizing the importance of the active process of cell-to-cell ROS signaling in communicating stress response signals between cells.

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Christopher S. Bond Life Sciences Center, University of Missouri, Columbia, MO, USA

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Prof. Amos Tanay & Prof. Yuval Eshed Dept. of Plant & Environmental Sciences  Faculty of Mathematics and Computer Science. Department of Molecular Cell Biology

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Prof. Avraham Levy Dept. of Plant and Environmental Sciences Weizmann Institute of Science

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Prof. Avraham Levy Dept. of Plant and Environmental Sciences Weizmann Institute of Science

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Gregor Mendel Institute of Molecular Plant Biology

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Faculty of Medicine, Technion

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University of Oxford

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University of York

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Temasek Life Sciences Laboratories

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MIT

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ETH Zurich

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Siobhan Brady Lab, UC Davis

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Israel Institute for Biological Research

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Prof. Avi Levy’s Lab Dept. of Plant and Environmental Sciences Weizmann Institute of Science

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Triterpenoids are a diverse class of secondary metabolites with important roles in plant defense, stress tolerance, and communication. In this study, we investigated the diversity and evolution of triterpenoids in plants using a combination of molecular, biochemical, and evolutionary approaches. Our results showed that various plant families have exploited the same evolutionary mechanism of molecular hijacking, whereby proteins involved in cell wall biosynthesis are co-opted for the production of triterpenoids. This process led to the formation of metabolons, which are protein complexes that facilitate the channeling of intermediates between enzymes in the biosynthetic pathway. Our study shows that the another gene involved in the pathway has undergone duplication and evolved to produce different types of metabolites in different Solanum species. Our findings provide insight into the complexity of plant secondary metabolism and the mechanisms underlying its evolution.

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Prof. Asaph Aharoni’s Lab Dept. of Plant and Environmental Sciences Weizmann Institute of Science

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Ofir Aharon Kuperman | PhD student- Natalio Lab Ben Labbel | PhD student- Vardi Lab Sam Lovat | Visiting student Lovat | Visiting student- Milo Lab

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Plants produce a vast range of specialized metabolites that serve various roles, including mediating interactions with their immediate environments and providing defence against (a)biotic stresses. The ‘omics era’ has brought a new golden age for plant specialized metabolism research, vastly accelerating the discovery of novel metabolites and our understanding of their biosynthesis, roles and regulation. Two studies exemplifying omics-driven discovery of metabolic pathways, in beet and in wheat, will be presented: 1. Betalains are red-violet and yellow pigments restricted to order Caryophyllales, which have attracted interest due to their health-promoting properties and use as food colorants. Transcriptomics-led discovery of enzymes catalyzing the last unknown step in betalain biosynthesis in red beet enabled us to heterologously produce these pigments in plants and microbes, providing a valuable platform for studying their in-planta roles and enabling their subsequent utilization as reporter genes and plant transformation markers. 2. Wheat is one of the most widely grown crops in the world but is susceptible to numerous pests and pathogens, leading to major annual losses. Despite its agricultural importance, current knowledge of wheat chemical defenses remains very limited. Using a genome mining approach we uncovered six previously unknown pathogen-induced metabolic pathways in hexaploid bread wheat, which produce a diverse set of molecules and are encoded by biosynthetic gene clusters. Discovery and characterization of these cluster-encoded metabolic pathways provides key insights into the molecular basis of biotic stress responses in wheat, thus opening new potential avenues for improvement of this major food crop.

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John Innes Centre

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Israel Oceanographic and Limnological Research

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Departments of Geography and Chemistry University of Zurich

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Viruses are the most abundant and diverse biological entities on Earth and can have a profound effect on biogeochemical cycles. In the sunlit ocean, viral lysis of 20-40% of hosts daily generates 20% of the dissolved organic carbon pool. Viruses can also affect their host’s metabolism during infection through expression of horizontally transferred host metabolic genes. While viruses in the ocean have been studied for over two decades, viral ecology and its effects have been neglected in other environments. I will present several of my studies that show how viruses in the ocean and in soil may affect their environment as well as ours through expression of metabolic genes and host-specific mortality. I’ll also discuss the current limitations in soil viral ecology, and technologies that can help us move forward.

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Ecole Centrale de Lyon- France

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The health of plants depends largely on their interactions with microbes. However, crop modernization affects these interactions, resulting in plants that rely on excessive inputs such as fertilizers, pesticides, irrigation, etc. Milpas are rain-fed polyculture agroecosystems found in Mesoamerica, where native maize landraces are grown in association with other species. Plant health in milpas is achieved with traditional practices and, therefore, plant-microbe beneficial interactions play an essential role in productivity. Milpas are central to the lives people in rural populations, as local or even familiar traditions, festivities and food preferences influence agricultural practices, resulting in unique characteristics of each parcel that potentially generates a wide diversity of beneficial plant-microbe interactions. In this seminar, we will review our recent progress in the study of beneficial microbe-plant interactions in milpas, including: 1) abundance, functions and structure of maize seed-endophytic communities comparing native vs. modern hybrid varieties, where the effect of modernization can be analyzed; and 2) the contribution of microbes for drought tolerance of native maize landraces adapted to arid regions, to explore the selection of microbes with specific beneficial functions as a result of the farmers’ preferences.

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CIAD Unidad Regional Hidalgo

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Prof. Uri Alon

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The Interuniversity Institute for Marine Sciences in Eilat

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Weizmann Institute of Science

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Algal blooms are events of high primary productivity and rapid population growth that can cover vast oceanic regions. They thus play an important role for the marine food web and for the global carbon and sulfur cycling. Furthermore, algal blooms are hotspots of microbial interactions with e.g. grazers, heterotrophic bacteria, fungi and viruses. These interactions are mediated by metabolite signals, they can modulate metabolic pathways and can induce biosynthetic gene clusters – the diversity of microbial communities in natural blooms is thus crucial in understanding the chemical ecology of algal blooms. In my talk, I will show how lipid remodeling during the infection of E. huxleyi blooms by its giant virus imprints the marine dissolved organic matter pool. Further, I will present how a tripartite interaction between alga, virus and associated microbes leads to a unique halogenation activity during bloom demise. Lastly, I will discuss the potential ecological role of indole derivatives that accumulate in the blooms of E. huxleyi.

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Institute of Science and Technology Austria

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Silberman Institute of Life Sciences, The Hebrew University

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Department of Integrative Biology The University of Texas at Austin

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School of Zoology, Faculty of Life Sciences, Tel-Aviv University

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Faculty of Life Sciences, BGU

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Nanyang Technological University, Singapore

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School of Integrative Plant Science, Cornell University

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Understanding how host–microbe homeostasis is controlled and maintained in plant roots is key to enhance plant productivity. However, the factors that contribute to the maintenance of this equilibrium between plant roots and their multikingdom microbial communities remain largely unknown. Using a microbiota deconstruction-reconstruction approach in gnotobiotic plant systems with synthetic, yet representative communities of bacteria, fungi, and oomycetes, we observe a link between fungal assemblages/load in roots and plant health. We show that modulation of fungal abundance in roots is tightly controlled by a two-layer regulatory circuit involving the host innate immune system on one hand and bacterial root commensals on another hand. We also report that fungi with the most detrimental activities in mono-association experiments with the host are part of the core root mycobiome in nature. Our results shed a light into how host–microbe and microbe–microbe interactions act in concert to prevent fungal dysbiosis in roots, thereby promoting plant health and maintaining growth-promoting activities of multikingdom microbial consortia.

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Department of Plant-Microbe Interactions, Max Planck Institute

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In plants, primary growth is sustained by a shoot apical meristem (SAM) that produce lateral leaf organs from their flanks until floral transition is attained. At this point, the SAM is marked by a dramatic doming of the SAM followed by either lateral formation of flowers e.g: Arabidopsis or by termination of by a flower as in determinate plants like tomato. Irrespective of the developmental track at the shoot apex, floral transition in both growth types is followed by the release of basal axillary buds from Apical Dominance, cues that are regularly emitted by the vegetative SAM. We use tomato shoot apices to understand the molecular changes that are triggered at floral transition by exhaustively profiling transcriptomes of individual SAMs. To that end, we identified dynamic, successive, transient gene expression programs activated along the developmental progression of SAM. I will present our results on how - genetic interrogation of components of these transient gene programs allowed dissociation of the tightly linked process of floral transition and apical dominance release. The relevance of these gene programs for flexibility to form simple to highly compound inflorescence structures will be discussed.

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Member Seminar Prof. Yuval Eshed Dept. of Plant and Environmental Sciences Weizmann Institute of Science

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Coccoliths are exoskeletal plates, made of highly complex microscopic calcite (CaCO3) crystals with astonishing morphological variety, produced by unicellular algae called Coccolithophores. For decades, their complexity has made coccolith fabrication and its controls alluring to scientists from different fields. Coccoliths grow intracellularly in a specialized vesicle where they presumably interact with chiral additives in a stereospecific manner. Such specific interactions are thought to give rise to numerous crystallographic faces, that convey ultrastructural chirality and convolutedness. We investigated the large coccoliths of Calcidiscus leptoporus by extracting them from within the cells along their growth, imagining them with various electron microscopy techniques at high resolution, and rendering their 3D structure. Our morphological analysis revealed that as the crystals mature, they transition from isotropic rhombohedra to highly anisotropic shapes, while expressing only a single set of crystallographic faces. This observation profoundly challenges the involvement of chiral modifiers. The crystals’ growth pattern showed that their shape is attained via differential growth rates of symmetry related facets with. Additionally, the rhombohedral geometry of the crystals appears to convey ultrastructural chirality in initial coccolith assembly stages. These findings change our understanding of biological control over complex crystal construction and mechanistically simplify the system in which they emerge.

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Assaf Gal lab

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An essential trait of plants is the ability to change intrinsic programs to align with external signals. Plants can sense their environment and respond by refining their development program. A good example of sensing and response is the behavior of stomata. Plant stomata optimize the assimilation of carbon dioxide (CO2) for use in photosynthesis while minimizing water loss. They do this in two ways: by physiological control of when they are open or closed and by developmental regulation of their abundance and pattern. Both modes of control can be regulated by the environment, and as we face future climate change, with an increase in average global temperatures and water limitation, the understanding of how plants optimize stomatal production and patterns with the environment has fundamental importance. Our fullest understanding of the genetic control of stomatal development is from work in Arabidopsis. Here, development involves a core set of transcription factors whose expression and activity are regulated by signals from neighbor cells, from distant parts of the plant and from environmental cues like light, temperature, osmotic stress, and CO2 levels. But while Arabidopsis is a powerful model for stomatal development, this research showed that tomatoes often lean on different cellular and genetic strategies to achieve optimal stomatal distributions. Using novel genetically encoded reporters and custom microscopy for developmental time-course analysis, we found that, like in Arabidopsis, tomato undergoes a series of asymmetric and symmetric cell divisions to produce stomata. However, we found that not all asymmetric divisions (ACDs) are the same; certain classes of ACDs are missing in the tomato epidermis, and instead other types of ACDs are used to generate non-stomatal cells. ACDs have been shown in both plant and animal systems to enable tunable development. This findings in tomato indicate that there are new types of ACDs that could mediate species-specific control of cell production and tissue organization.

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Prof. Dominique Bergmann Lab Stanford University Howard Hughes Medical Institute

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While many natural and artificial surfaces may appear dry, they are in fact covered by thin liquid films and microdroplets invisible to the naked eye, known as microscopic surface wetness (MSW). Central to the formation and retention of MSW are the deliquescent properties of hygroscopic salts that prevent complete drying of wet surfaces, or that drive the absorption of water until dissolution when the relative humidity is above a salt-specific level. As salts are ubiquitous, MSW occurs in many microbial habitats such as soil, rocks, plant leaf and root surfaces, the built environment, and human and animal skin. While key properties of MSW, including very high salinity and segregation into droplets, greatly affect microbial life therein, it has been scarcely studied, and systematic studies are only in their beginnings. Based on recent findings, we propose that the harsh micro-environment that MSW imposes, which is very different from bulk liquid, affects key aspects of bacterial ecology including survival traits, antibiotic response, competition, motility, communication, and exchange of genetic material. In this talk I will discuss some of these aspects and highlight recent work from our lab showing how MSW affects horizontal gene transfer, antibiotic response, and interspecies competition. As MSW is typical to many terrestrial microbial habitats, studying microbial life in MSW will be imperative for understanding microbial ecology in vast terrestrial habitats, affecting global biogeochemical cycles, as well as plant, animal, and human health.

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Department of Plant Pathology and Microbiology, Faculty of Agriculture, HUJI

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Chemical reactions serve as central units for cellular information processing and control. However, reaction chemistry inside cells is “noisy”, leading to significant variability in the molecular constitution of living systems. How cells control and mitigate noise when precision is important is still poorly understood. In this talk, I will show that compartmentalization of protein via phase separation provides a potential cellular mechanism to protect biochemical pathways against noise. Using a simple theoretical model that links protein concentration fluctuations to the physics of phase separation I will show that noise can be significantly attenuated in the presence of phase separated compartments. I will then present experimental single-cell data in engineered and endogenous condensates, which support this prediction. I will conclude my talk by discussing potential implications and future challenges.

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Max Planck Institute

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We are studying the mechanistic basis of epigenetic regulation in the Polycomb system, a vital epigenetic silencing pathway that is widely conserved from flies to plants to humans. We use the process of vernalization in plants in our experiments, which involves memory of winter cold to permit flowering only when winter has passed via quantitative epigenetic silencing of the floral repressor FLC. Utilising this system has numerous advantages, including slow dynamics and the ability to read out mitotic heritability of expression states through clonal cell files in the roots. Using mathematical modelling and experiments (including ChIP and fluorescent reporter imaging), we have shown that FLC cold-induced silencing is essentially an all-or-nothing (bistable) digital process. The quantitative nature of vernalization is generated by digital chromatin-mediated FLC silencing in a subpopulation of cells whose number increases with the duration of cold. We have further shown that Polycomb-based epigenetic memory is indeed stored locally in the chromatin (in cis) via a dual fluorescent labelling approach. I will also discuss how further predictions from the modelling, including opposing chromatin modification states and extra protein memory storage elements, are being investigated. I will also discuss the mechanisms by which long term fluctuating temperature signals are sensed before being converted into digital chromatin states for long term memory storage.

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John Innes Centre, UK

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Many plant foods contain oxalate C2O4(-2) that reaches the colon when we eat plant foods. When oxalate reaches high concentrations it can crystalize together with Ca+2 to form kidney stones. Humans don’t have enzymes to degrade oxalate, but microbes do. Therefore oxalate-degrading probiotics are a potential treatment for hyperoxaluria. Since clinical trials with oxalate-degrading microbes, like Oxalobacter Formigenes, could not show oxalate reduction, additional microbes that can degrade oxalate are of high interest, especially those that can perform in the human gut. In my talk I will describe how we harnessed lab evolution to develop novel gut microbes that can degrade oxalate. We obtained E. coli isolates from the stool of human volunteers and evolved them to metabolize oxalate in an anaerobic chamber. While no E. coli is known to utilize oxalate, our isolates evolved robust growth on oxalate as a sole source of carbon and energy. In my talk I will present findings on the genetic and molecular mechanism underlying this evolution.

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Faculty of Agriculture The Hebrew University

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Steroidal alkaloids and their glycosylated forms (SGAs) are a well-known group of specialized metabolites produced by Solanaceae species. In tomato, almost 100 steroidal alkaloids were detected, α-tomatine being the most predominant in leaves, flower buds and green fruit tissues. When consumed, high concentrations of α-tomatine in food are associated with bitter taste and burning sensation in the throat. In the course of tomato fruit ripening the shift in the SGA profile occurs towards the non-bitter and non-toxic esculeosides by extensive modification of the entire pool of α-tomatine by hydroxylation, acetylation, and glycosylation. Nevertheless, wild accessions exist, that display high levels of α-tomatine in fully ripe fruits. In this study, we aimed at deciphering the molecular mechanism(s) by which ripe tomato fruit of natural species and commercial varieties maintained low α-tomatine levels and stayed non-bitter. We discovered that GORKY, a member of the nitrate and peptide family (NPF) of transporters, is essential for preventing high α-tomatine levels in ripe tomato fruit. GORKY is responsible for relocating α-tomatine and other steroidal alkaloids from the vacuole to the cytosolic domain during ripening. This facilitates the metabolic conversion of the entire α-tomatine pool to non-bitter forms rendering the fruit more palatable. Hence, the discovery of GORKY action provides a molecular mechanism for a vital process that renders tomato fruit attractive to frugivores in nature and commercial tomato varieties delicious to consumers.

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Dept. of Plant and Environmental Sciences Weizmann Institute of Science

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Insects and other arthropods are central to the terrestrial food-webs and play important ecological roles, such as in nutrient cycling and pollination. Recent studies suggest significant declines in arthropod populations, including in abundant species, with potential widespread consequences -- 'the insect apocalypse'. Such challenging studies typically monitor relative measures of the overall biomass or abundance. However, absolute measures are often required in order to gain a holistic understanding of the state of terrestrial arthropods, their ecological significance, and the consequences of their possible decline.

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Dept. of plant and Environmental Sciences- WIS

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Plants adopt a variety of life history strategies to succeed in the Earth’s diverse environments. Using functional traits which are defined as “morphological, biochemical, physiological, or phonological” characteristics measurable at the individual level, plants are classified according to their species’ adaptative strategies, more than their taxonomy, from fast growing plant species to slower-growing conservative species. These different strategies probably influence the input and output of carbon (C)- resources, from the assimilation of carbon by photosynthesis to its release in the rhizosphere soil via root exudation. However, while root exudation was known to mediate plant-microbe interactions in the rhizosphere, it was not used as functional trait until recently. In addition, no study analyzed the impact of plant nutritional strategy via root exudation quality and quantity on rhizosphere microbial activities and diversity. Here, we (i) assess whether root exudate levels are useful plant functional traits in the classification of plant nutrient-use strategies and (ii) determine using stable isotope probing (SIP) approach the impact of root exudates quality and quantity on active microbiota diversity and activity. For this purpose, six grass species distributed along a gradient of plant nutrient resource strategies, from conservative species, characterized by low nitrogen (N) uptake, a long lifespans and low root exudation level, to exploitative species, characterized by high rates of photosynthesis, rapid rates of N uptake were used. We show, for the first time, that root exudation rate can be used as a key functional trait in plant ecology studies and plant strategy classification. In addition, measurement of microbial activities revealed an increase in denitrification and respiration activities for microbial communities colonizing the root adhering soil of exploitative species. This increase of microbial activities results probably from a higher exudation rate and more diverse metabolites by exploitative plant species. Furthermore, our results demonstrate that plant nutrient resource strategies have a role in shaping active microbiota. We present evidence demonstrating that plant nutrient use strategies shape active microbiota involved in root exudate assimilation and soil organic matter degradation via root exudation.

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Biosciences Department, Institut National des Sciences Appliquées de Lyon

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Institute of Integrative Genome Biology and Department of Botany and Plant Sciences UC Riverside, USA

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The poles of rod-shaped bacteria are emerging as a “microBrain”, serving as hubs for sensing and regulation. Not only do they contain specific proteins, but we have shown that they contain a unique RNA population, which includes most small regulatory RNAs (sRNA). Upon stress, most sRNAs massively accumulate at the poles with the RNA chaperone Hfq. We have recently provided a proof-of-concept for the existence of a polygenic plan for sRNA-mediated regulation, with the poles providing an arena for its implementation. In my talk, I will show that the mechanism underlying this plan is assembly of Hfq with polar condensates, which a new pole-localizer, TmaR, forms by liquid-liquid phase separation (LLPS). I will further show that this LLPS-driven membraneless polar organelle serves as a hub for regulating various bacterial survival strategies.

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Dept. of Microbiology and Molecular Genomics, The Hebrew University

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Diatoms are among the most globally distributed and ecologically successful organisms in the modern ocean, contributing upwards of 40% of total marine primary productivity. Diatom production is tightly coupled with carbon export through the ballasted nature of the silica-based cell wall, linking the oceanic silicon and carbon cycles. While viruses are considered key players in ocean biogeochemical cycles, little is known about how viral infection specifically impacts diatom populations. Using a suite of molecular, physiological and geochemical approaches, we explored diatoms and associated viruses across diverse nutrient regimes in the northeast Pacific. We found that silicon (Si) limitation facilitated virus infection and mortality in diatoms while the onset of iron (Fe) limitation, in sharp contrast, substantially reduced viral replication. These findings, recapitulated in model systems, suggest that virus-mediated mortality in Si-limited regimes would facilitate diatom remineralization in the surface ocean, while diatoms in Fe-limited regimes may escape viral lysis, ultimately contributing to carbon export. We also explored how viral infection of diatoms might impact the microbial processing of organic matter in the ocean. Using bacterial isolates and model diatom host-virus systems, we tested how bacteria respond to dissolved organic matter generated during viral infection in diatoms. We found that this material can significantly stimulate ectoproteolytic activity, implicating viral infection of diatoms in bacteria-mediated recycling of organic matter and silica in the surface ocean. Together, these findings highlight the dynamic role that diatom host–virus interactions play in shaping the biogeochemical landscape the global ocean.

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Faculty of Life Sciences, Bar-Ilan University

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Microbes use protein toxins to kill competitors and to infect host cells. Discovering new toxins and describing their function is important to understand processes in microbial ecology and host-microbe interactions. Moreover, the toxins can be used in various applications, including drugs, pesticides, vaccines, potent enzymes, etc. We study toxins in the lab by combining large-scale computational genomics and molecular microbiology. In the talk, I will tell two recent stories from the lab on microbial toxins and their secretion systems. The first study is about the mysterious extracellular contractile injection system. This toxin delivery system evolved from a phage into a molecular weapon employed by bacteria against eukaryotic cells. In the second study, I will tell about the exciting group of polymorphic toxins. These are large toxin proteins that undergo recombination to create large diversity of antimicrobial toxins. We developed methods to discover toxins from both groups, study the ecological role of the toxins, and their molecular function. These approaches led to discovery of over 30 novel microbial toxins that we study in the lab.

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The Hebrew University of Jerusalem

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Epicuticular waxes coat the aerial parts of land plants almost ubiquitously. These waxes consist mainly of very long chain fatty acids and their derivatives, though epicuticular wax exact composition may vary greatly between plant species. Despite their wide distribution and decades of extensive study, the role of cuticular lipids in sustaining plant fitness is far from being understood. The main goal of my PhD research has been therefore to answer this fundamental question. To this end, I identified 16 different cuticular lipid related genes based on their enriched expression in the leaf epidermis and slight drought induction and generated knock out mutations in these genes using the CRISPR Cas9 system. Of these 16 mutants, nine displayed a cuticular lipid related phenotype and five were selected for further analysis. The mutated plants had a reduced wax load, or were completely lacking certain wax components altogether. This led to drastic shifts in wax crystal structure and to elevated cuticular water loss, although under non stressed conditions plants with an altered wax composition did not have elevated transpiration. In contrabst, once exposed to drought plants lacking alkanes were not able to strongly reduce their transpiration, leading to leaf death and impaired recovery upon resuscitation. When interactions of snails and insects with this mutant populations were examined, I found that these interactions were best divided based on their type – leaf chewing, phloem feeding or non-feeding interactions. Here I found that fatty alcohols were correlated with reduction in caterpillar weight gain, while cutin but not wax composition affected phloem feeders. Non feeding interactions examined in tobacco white fly showed an effect of wax crystal structure rather than chemical composition. Finally, to examine the effects of epicuticular wax under natural conditions two field plots were planted with these mutants and monitored during several months. I found, that similar to the results of the drought trials, under non-competitive conditions epicuticular wax had little effect on plant fitness. however, when plants were under severe competition with foreign plants, all wax components contributed greatly to fitness. in these plots, similar to the caterpillar assays, caterpillars from a wider range of species preferred the fatty alcohol devoid far mutants. These were also preferred by web weavers, and especially spiders. From this diverse range of settings and interactors I concluded that under optimal conditions, epicuticular wax has little effect on plant fitness. however, once conditions are stressful epicuticular wax contributes greatly whether these conditions be drought, competing vegetation or insect herbivores eating the plants’ leaves. That being said, not all wax components contribute equally to every process. Alkanes are essential for drought recovery while fatty alcohols reduce insect herbivory.

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The sinking of organic particles in the ocean and their degradation by marine microorganisms drive one of the most conspicuous carbon fluxes on Earth, the biological pump. Yet, the mechanisms determining the magnitude of the pump remain poorly understood, limiting our ability to predict this carbon flux in future ocean scenarios. Current ocean models assume that the biological pump is governed by the competition between sinking speed and degradation rate, with the two processes independent from one another. In this talk, I will demonstrate that contrary to this paradigm, sinking itself is a primary determinant of the rate at which bacteria enzymatically degrade particles in the ocean. By combining video microscopy and microfluidic experiments to directly observe and quantify bacterial degradation of individual organic particles in flow, I will show that even modest sinking speeds of 8 meters per day enhance degradation rates more than 10-fold. I will further discuss the molecular mechanism behind the sinking-enhanced degradation, as well as possible ways by which bacteria can slow the sinking of particles. Finally, using the results obtained from a mathematical model, I will show that the coupling of sinking and degradation may contribute to determining the magnitude of the vertical carbon flux in the ocean, and will outline major open questions in the field.

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Prof. Roman Stocker Lab ETH Zurich

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The sinking of organic particles in the ocean and their degradation by marine microorganisms drive one of the most conspicuous carbon fluxes on Earth, the biological pump. Yet, the mechanisms determining the magnitude of the pump remain poorly understood, limiting our ability to predict this carbon flux in future ocean scenarios. Current ocean models assume that the biological pump is governed by the competition between sinking speed and degradation rate, with the two processes independent from one another. In this talk, I will demonstrate that contrary to this paradigm, sinking itself is a primary determinant of the rate at which bacteria enzymatically degrade particles in the ocean. By combining video microscopy and microfluidic experiments to directly observe and quantify bacterial degradation of individual organic particles in flow, I will show that even modest sinking speeds of 8 meters per day enhance degradation rates more than 10-fold. I will further discuss the molecular mechanism behind the sinking-enhanced degradation, as well as possible ways by which bacteria can slow the sinking of particles. Finally, using the results obtained from a mathematical model, I will show that the coupling of sinking and degradation may contribute to determining the magnitude of the vertical carbon flux in the ocean, and will outline major open questions in the field.

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Prof. Roman Stocker Lab ETH Zurich

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Relationships between gut microbial ecosystems and their vertebrate hosts have been shown in recent years to play an essential role in the well-being and proper function of their hosts. In my lecture, I will discuss some of our recent findings regarding such ecosystems stability, development, and interaction with the host.

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The Department of Life Sciences & the National Institute for Biotechnology in the Negev, Ben Gurion University

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Plants continuously monitor the presence of microorganisms through their immune system to establish an adaptive response. Unlike immune recognition of pathogenic bacteria, mechanisms by which beneficial bacteria interact with the plant immune system are not well understood. Analysis of colonization of Arabidopsis thaliana by auxin producing beneficial bacteria revealed that activating the plant immune system is necessary for efficient bacterial colonization and auxin secretion. A feedback loop is established in which bacterial colonization triggers an immune reaction and production of reactive oxygen species, which, in turn, stimulate auxin production by the bacteria. Auxin promotes bacterial survival and efficient root colonization, allowing the bacteria to compete with other members of the root microbial community and inhibit fungal infection, promoting plant health.

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Prof. Philip Benfey Lab, Duke University, USA

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Lab of Prof. Dan Kliebenstein, Department of Plant Sciences, UC Davis, USA

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Prof. Rotem Sorek's Lab., Department of Molecular Genetics, WIS

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Prof. Avraham Levi's Lab., Dept. of Plant and Environmental Sciences

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The Interuniversity Institute for Marine Sciences in Eilat & Silberman Institute of Life Sciences, Hebrew University of Jerusalem

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Senior Lecturer, Dept. of Plant Pathology and Microbiology, The Hebrew University of Jerusalem (Rehovot Campus)

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Professor (emeritus) of Biological Oceanography and Marine Ecology, The Interuniversity Institute for Marine Sciences and Department of Ecology, Evolution & Behavior, The Hebrew University, Eilat

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Prof. Ron Milo's lab. Department of Plant and Environmental Sciences

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Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, MIT, Cambridge MA, USA

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PhD Student, Assaf Gal Lab, Department of Plant and Environmental Sciences

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PhD student, co-advised by Prof. Amos Tanay, Faculty of Mathematics & Computer Science and Prof. Yuval Eshed, Department of Plant and Environmental Sciences

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Roy J Zuckerberg Career Development Chair for Water Research, Department of Environmental Hydrology & Microbiology, Zuckerberg Institute for Water Research (ZIWR), The Jacob Blaustein Institutes for Desert Research (BIDR), Ben-Gurion University of the Negev

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School of Molecular Sciences/The Biodesign Institute, The Center for Applied Structural Discovery, Arizona State University

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Plant Sciences and Genetics in Agriculture, The Robert H Smith Faculty of Agriculture, Food and Environment, Rehovot