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CSB Seminar Series – Cedoljub Bundalovic-Torma & Fabien Lonjon – University of Toronto

April 22, 2022 @ 11:00 am - 12:00 pm

TITLE: Reconstructing the Evolutionary Landscape of The Pseudomonas syringae Effectorome Through a Novel Ancestral Lineage Reconstruction Approach

Dr. Cedoljub Bundalovic-Torma
Postdoctoral Fellow, Guttman Lab
Department of Cell & Systems Biology
University of Toronto

Next-generation sequencing has provided us with an unprecedented ability for studying bacterial populations and understanding from an evolutionary perspective how genetic diversity has given rise to novel adaptive phenotypes. Toward this end, the Guttman Lab has recently performed a comparative genomics survey of the evolutionary diversity of the plant pathogen Pseudomonas syringae which has provided a comprehensive glimpse of the diversity of type III secreted effector protein family cargoes that underlie its capacity to cause disease or elicit immunity on a wide variety of hosts. This work presents a prime opportunity for investigating the evolutionary processes have shaped the emergence of effector arsenals and the evolution of host-specificity across the P. syringae species complex.

An important challenge faced when studying bacterial populations is that features/traits/phenotypes of interest can emerge through a variety of evolutionary processes, including sequence divergence, loss, and gain through horizontal gene transfer. However, traditionally used measures used for quantifying diversity, such as prevalence (the proportion of features of interest in the population) and phylogenetic diversity, either do not account for population structuring or recombination making them inapplicable for the study of bacterial populations. To overcome these limitations we developed a novel recombination-aware phylogenetic diversity metric, RecPD, for generally assessing the diversity of bacterial features, e.g. phenotypes or gene families, based on ancestral reconstruction of their phylogenetic distributions. We applied RecPD to assess the phylogenetic diversity and quantify recombination across 70 effector families distributed across 494 P. syringae species complex phylogeny, encompassing strains isolated from diverse phylogroups, pathovars, and crop plant hosts. We observed that recombination has occurred across a substantial proportion of effector families and demonstrate that prevalence is a wholly inappropriate measure of feature/trait diversity. Furthermore, we found that effector families which have undergone a greater extent of recombination also showed a significant enrichment for immune-eliciting alleles, raising the fascinating question for future investigation of whether host immunity is a driver or response to the horizontal acquisition of effector families in P. syringae, and its consequence on determining host range.

– Followed by –

TITLE: Exploring the Immunodiversity of Tomato Against Pseudomonas syringae

Dr. Fabien Lonjon
Postdoctoral Fellow, Guttman Lab
Department of Cell & Systems Biology
University of Toronto

Pseudomonas syringae is a highly diverse bacterial species complex that includes strains capable of infecting almost all agronomically important crops. P. syringae pathogenicity relies on its type III secretion system (T3SS), which secretes type III effector (T3SEs) proteins directly into the plant cells. T3SEs are crucial virulence factors used to suppress plant basal immunity in order to cause successful infections. In response, plants have developed mechanisms to detect specific T3SEs through nucleotide-binding leucine-rich repeat receptors (NLRs) in order to trigger a robust immune response called effector-triggered immunity (ETI). To better understand T3SE diversity and how this diversity influences plant immunity, a P. syringae type III effector compendium (PsyTEC) was developed, which encompasses the global species diversity of T3SEs. We infected a cultivated tomato variety, Solanum lycopersicum cv. Glamour, with PsyTEC and identified 17 alleles from five T3SE families, including four uncharacterized, that elicit an immune response. In order to identify additional sources of resistance, we extended our PsyTEC screen to three wild relatives of tomato species: Solanum arcanum, Solanum galapagense and Solanum pimpinellifolium. Surprisingly, no new elicitor of tomato immunity were identified, suggesting that most of the immunodiversity in wild tomato is retained in domesticated crops. Finally, we found that 30% of P. syringae strains harbor at least one ETI eliciting T3SE in tomato, and that these T3SEs may limit host range of P. syringae strains. In addition, our most recent efforts on mapping novel tomato resistance genes against P. syringae T3SE will be presented. These novel resistance genes promise new tools to engineer more durably resistant tomato cultivars against virulent P. syringae strains.


LOCATION: Sidney Smith Hall, Room 2125 / Virtual

Zoom ID and passcode:


Meeting ID: 874 4742 2547

Passcode: 050579


April 22, 2022
11:00 am - 12:00 pm
Event Category:


Sidney Smith Hall, Room 2125
100 St. George Street
Toronto, Ontario M5S 3G3
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