Dr. Sonali Roy Noble Research Institute Regulation of Nitrogen Acquisition by Peptide Hormones
The root system of a plant performs vital functions including resource uptake when nutrient availability in soil is non-homogenous; while also providing a surface for interactions with beneficial microbes. Legume roots tolerate deficiency of the macronutrient Nitrogen by not only enhancing its direct uptake but also by establishing a unique symbiotic relationship with soil bacteria called rhizobia. Here I present findings that put genome-encoded small secreted peptides or ‘peptide hormones’ at the center-stage of N-acquisition in legumes. Our findings suggest that peptides likely provide a cheap, environmentally-friendly, non-GMO route to address current challenges of plant growth in nutrient-deprived soils.
Checkmate: You've been ubiquitinated! Investigating ubiquitin-mediated turnover of BIK1, a key plant immune signalling kinase
Plants are susceptible to infection from bacterial, fungal, and viral diseases; although they cannot run away, they are far from defenseless! Plants have complex immune systems that are responsible for the detection of pathogens and initiating signal transmission in order to respond to and fight off infections. BOTRYTIS INDUCED KINASE 1 (BIK1) is a key regulator of immune signaling that is required for protection against multiple types of pathogens. BIK1 is activated through phosphorylation by plasma-membrane receptor kinases and in turn phosphorylates and activates other downstream proteins. To prevent overactive immune responses, accumulation of BIK1 is tightly regulated through ubiquitination by PLANT U-BOX 25 and subsequent degradation by the proteasome. This thesis investigates the functional importance of ubiquitination on BIK1 and how ubiquitination impacts BIK1 turnover. We identified nine BIK1 ubiquitination sites using highly sensitive mass spectrometry. Higher order ubiquitin-ablative mutants were generated to determine which terminal residues are important for proteasomal turnover. We verified that BIK1 ubiquitin-ablative mutants were catalytically active and appropriately localized to the plasma membrane and nucleus when transiently expressed in tobacco. Using a semi-in vivo approach, I demonstrate that ablating all nine of these BIK1 ubiquitination sites slows the rate of degradation and therefore may be important for regulating BIK1 levels in plants. Genetic analyses were explored using mutated BIK1 variants in a bik1 knockout or WT background but yielded inconclusive data. This work contributes to the growing body of literature on post-translational modification by ubiquitination and highlights that, unlike certain post-translational modifications which are highly residue specific (ie phosphorylation), ubiquitination substrate specificity is likely less critical at the residue level.
Dr. Peter Mergaert Centre National de la Recherche Scientifique Role of antimicrobial peptides and the ROS-producing enzyme Duox in insect gut symbiosis
Most animals harbor a gut microbiota that consists of potentially pathogenic, commensal and mutualistic microorganisms. In insects, antimicrobial peptides (AMPs) and the reactive oxygen species (ROS)-producing enzyme “Dual oxidase” (Duox) are the central regulators of gut mucosal immunity. They antagonize pathogenic bacteria and maintain gut homeostasis. However, the non-specific harmful activity of AMPs and ROS on microorganisms raises the question about the role of AMPs and Duox in the maintenance of mutualistic gut symbionts. In my seminar, I will highlight how AMPs and Duox control the establishment of a specific gut symbiosis in the bean bug Riptortus pedestris, which harbors in a symbiotic compartment of the midgut the mutualistic bacterium Burkholderia insecticola. We have demonstrated that symbiosis-specific as well as immunity-specific AMPs are produced massively during B. insecticola infection of the gut and that resistance to these AMPs is crucial for the capacity of the bacterium to colonize the gut. On the other hand, and contrarily to our initial expectation, we found that Duox-dependent ROS did not directly contribute to epithelial immunity in the midgut in response to B. insecticola or to pathogenic bacteria. Instead, we demonstrated that Duox is essential for symbiosis and the colonization of the gut by the aerobic B. insecticola by mediating the formation of a respiratory network enveloping the gut.
Dr. Sylva Donaldson Ilchyna Centre for the Analysis of Genome Evolution and Function, University of Toronto
Alternative Academic Career Trajectory
When you’re in graduate school, it often feels like the default career path is to become a professor. You’re trained to manage your own research program, teach courses and supervise others. What do you do if you stayed in your postgraduate training because you love research but don’t see yourself in a tenure track position in the future? Congratulations! You are opening the door to an alternative academic career! What does that mean? … anything you want, really. I think of it as a career for someone with a postgraduate degree that is not a tenure-track position. It’s a pretty open definition ¯\_(ツ)_/¯. But that doesn’t mean that you have to jump from one short-term contract to another. There is plenty of opportunity for job security! I’ll be talking about my path to a long-term and stable alternative academic career. I will present a number of my own failures (#normalizefailure) and successes. I will also reassure you that it is possible to have a rewarding scientific alternative academic career and a fulfilling life outside your career.
Innovation, conservation, and repurposing of gene function in plant root cell type development
Irrespective of species, plant roots have remarkably similar patterning, and thus, many cell types are considered functionally homologous across species. Despite these similarities, there is also diversity in root cell types, such as the exodermis, which is present in a reported 89% of angiosperms, but absent in the intensely studied model species Arabidopsis (Perumalla, Peterson, and Enstone 1990). Additionally, multiple cortical cell types exist in species like tomato and rice (Henry et al. 2015), but only a single cortical cell type exists in Arabidopsis. To understand this diversity we profiled tomato root cell type translatomes and chromatin accessibility. Using xylem differentiation in tomato, relative to Arabidopsis, examples of functional innovation, repurposing and conservation of transcription factors are described. Repurposing and innovation of genes are further observed within an exodermis regulatory network and illustrate its function. Finally, we extend these comparisons between Arabidopsis and tomato, to rice, and explore the question of homology between cell types across diverse species.