Dr. Kenji Nakahara, Lecturer
Pathogen-Plant Interactions Group, Research Faculty of Agriculture,
Hokkaido University, Sapporo, Hokkaido 060-8589, Japan

RNA silencing is one of major antiviral systems in plants and most plant viruses encode RNA silencing suppressors (RSS) to facilitate their infection of plants by inhibiting the plant’s endogenous antiviral RNA-silencing machinery. Previously, a tobacco calmodulin-like protein (CML), termed rgs-CaM, has been reported to interact with HC-Pro and 2b, which are RSSs encoded by members of the genus Potyvirus and Cucumovirus, respectively. We have shown that the tobacco CML counteractively functions as an antiviral defense factor to direct degradation of its interacting RSS proteins via autophagy. Further studies suggest that the rgs-CaM-mediated counterdefense against RSSs involves salicylic acid signaling. Plants encode dozens of CMLs (50 and 32 CMLs in Arabidopsis and rice, respectively). Several CMLs of tobacco and other plants are similar to rgs-CaM in their amino acid sequences, suggesting possible binding to viral RSSs and involvement with antiviral defense. We have been investigating whether Arabidopsis CML orthologs of rgs-CaM may be involved in plant/virus interaction and I will present data from research in Japan and recent collaborative work in the Snedden lab here at Queen’s.

Gustavo MacIntosh // Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology; Iowa State University, Ames, IA, USA
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Ribosomes are essential cellular components, and a large proportion of cellular resources are dedicated to their synthesis. Yet, the pathways involved in the turnover of normal ribosomes remain poorly studied. We have shown that the Arabidopsis ribonuclease RNS2 functions in the vacuolar degradation of rRNA. Mutants lacking this RNase activity have rRNA with a longer half-life, which accumulates in the vacuole. rns2 mutants also have constitutive activation of the autophagy pathway, possibly as an attempt to compensate for the loss of rRNA degradation. A functional autophagy pathway is also necessary to maintain normal RNA levels in Arabidopsis, suggesting that plants use an autophagy-dependent mechanism to transport ribosomes to the vacuole for recycling. However, differential rRNA accumulation in vacuoles of specific atg mutants suggest that rRNA or ribosome transport to the organelle may normally occur through a selective mechanism that utilizes some, but not all, the autophagy core components. In addition to dissecting the rRNA decay pathway and the mechanisms of rRNA transport to the vacuole, we are interested in understanding why rRNA is recycled. Metabolome and transcriptome analyses indicated that carbon flux through the pentose phosphate pathways is altered in mutants that cannot recycle rRNA properly. Our results suggest that rRNA turnover is necessary to maintain cellular homeostasis, likely as part of the nucleoside salvage pathway. When this salvage pathway is blocked, the PPP is rerouted to produce ribose-5-P for de novo nucleoside synthesis. This change in carbon flux, in turn, causes growth phenotypes and the production of reactive oxygen species that are responsible for activation of the general autophagy pathway in rns2 mutants.

Cyril Zipfel // Institute of Plant and Microbial Biology, Zürich-Basel Plant Science Center University of Zürich, Switzerland
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Plants genomes encode hundreds of cell surface-localized receptor kinases that control almost all aspects of plant life, ranging from reproduction, growth to responses to the external environment. Using receptor kinases that function as immune receptors by perceiving microbial elicitors, we are studying the molecular basis of plant immunity, but also more generally how plant receptor kinases work at the mechanistic level. Using the leucine-rich repeat receptor kinases FLS2 and EFR (which perceive bacterial flagellin and EF-Tu, respectively) as model systems, we are investigating how plant receptor kinases function as part of multimeric protein complexes at the plasma membrane – often in complex with other receptor kinases, which act as regulatory proteins. I will present our recent work that uncovered the importance of these regulatory receptor kinases and receptor kinase-associated proteins in controlling the assembly and activity of functional heteromeric receptor complexes. 

Special Biology Seminar: Biological Sciences room 3110, Monday June 3, 11:30 - 12:30

Kristen Siegel, MSc Candidate, Dept Biology, Queen's University, Monaghan Lab
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Stomata are microscopic pores found in leaf epidermal tissue that facilitate gas exchange between a plant and its environment during photosynthesis. Each pore is bordered with two specialized guard cells, which can modulate their turgidity to cause stomatal opening or closure. Photosynthetically favourable conditions, such as high levels of blue light, induce stomatal opening through guard cell water uptake. However, these openings are also commonly seized as a point of entry for plant microbial pathogens. Upon pathogen detection, plasma membrane-localized receptors will initiate intracellular signalling cascades, and ultimately cause stomatal closure though water efflux and guard cell deflation. This process, known as stomatal defense, contributes to a broad-spectrum immune response which is sufficient to defend against most pathogens. In a proteomics-based screen for regulators of immunity in Arabidopsis thaliana, we identified components of stomatal defense as well as several proteins with unknown function. Of particular interest was a novel protein belonging to a small family of mitogen-activated protein kinases involved in blue-light induced stomatal opening. This work investigates the putative role of this family in stomatal defense and immune signalling.

Irina Sementchoukova, MSc candidate, Monaghan Lab, Dept Biology, Queen's 

Pseudomonas syringae is a bacterial pathogen that causes disease in a broad range of plant species.  As a part of its infection strategy, P. syringae releases virulence factors called effectors into plant cells to disarm host defenses. In response to effector sabotage, plants evolved intracellular NUCLEOTIDE BINDING AND LEUCINE RICH REPEAT RECEPTORS (NLRs) that ‘guard’ the integrity of critical immune signalling components prone to be effector targets. When no damage is detected, NLRs remain in the ‘OFF’ state, and only turn ‘ON’ when perturbations are detected in the guarded protein. Activated NLRs typically result in a form of programmed cell death at the site of infection that protects surrounding uninfected tissues. MEMBRANE ATTACK COMPLEX/PERFORIN (MACPF) proteins are well known agents of defense in the mammalian immune system, though the molecular function of this protein family in plants has not been established. The model plant Arabidopsis thaliana encodes four MACPF domain proteins, and genetic evidence suggests that at least two of these proteins are involved in the plant immune response. Interestingly, loss-of-function mutations in these loci result in hyperactive immune signaling and cell death, reminiscent of dysregulated NLR activation.  My project has thus been focused on determining if MACPF proteins may be effector targets guarded by plant NLRs.

Dr. Dawn Hall, Office of the Chief Information Officer, Treasury Board of Canada Secretariat, Government of Canada
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When I obtained a PhD in Biology in 2007, I never would have predicted what the next 10+ years of my career would bring. This talk will begin with a retrospective look at my time as a PhD student and post-doc, followed by a description of the career experiences that have followed: from science communication and exhibit content development at the Ontario Science Centre, to exhibit interpretation for the renewal of the Canada Science and Technology Museum, to my current role as an analyst/advisor with the Government of Canada. Throughout, I will discuss the decisions that I made, and how the skills that were developed during my PhD and post-doc were applied in the jobs that have followed. I will also share lessons learned and perspectives from the career journey. 

Dr. Louise Winn, Dept of Biomedical and Molecular Sciences, Queen's University

​Drugs and environmental chemicals can harm the developing fetus by causing not only the commonly appreciated structural defects such as cleft lip, but also biochemical and functional abnormalities related to alterations in membranes as well as enzymes and other proteins. These compounds can also disrupt normal metabolic and endocrine signalling via epigenetic modifications, including DNA methylation, histone modifications, and/or RNA-mediated silencing of genes through miRNA, resulting in negative health outcomes later-in-life.My research program aims to investigate mechanisms of in utero initiated developmental toxicity employing a combination of expertise in biochemical and morphological assessment of chemical toxicity, and molecular toxicological approaches. Our goal is to answer fundamental mechanistic questions about the biological effects of in utero exposures to drugs and environmental chemicals to inform exposure monitoring practices, policy and human health assessments.

Dr. Matsuo Uemura, Faculty of Agriculture, Iwate University, Morioka, Japan

Freezing stress is one of the most important limiting factors of plant survival. Plants have developed a freezing adaptation mechanism upon sensing low temperatures (cold-acclimation). Compositional changes in the plasma membrane, one of the initial sites of freezing injury, is prerequisite of achieving cold acclimation and have been investigated in several plant species. However, the cold dehardening process at elevated temperatures (de-acclimation) has not yet been fully characterized. Here we conducted shotgun proteomics with label-free semiquantification on plasma membrane fractions of Arabidopsis leaves during cold acclimation and de-acclimation. A list of 873 proteins with significantly changed proteins in response to the two processes was obtained. Although the cold-acclimation-responsive proteins were globally returned to non-acclimated levels by de-acclimation, several representative cold-acclimation-responsive proteins tended to remain at higher abundance during de-acclimation process. Our results suggest that plants deharden right after cold acclimation to restart growth and development but some protein changes of the plasma membrane may be maintained to cope with the threat of sudden freezing during deacclimation process.