PhD Transfer Exam – Eliana Vonapartis (Gazzarini lab)

PhD Transfer Exam

Wednesday May 11^th, 12:10 pm – Room SW 403, University of Toronto at Scarborough

Eliana Vonapartis (Gazzarrini lab)

“Investigating the Role of XERICO in GA-ABA Crosstalk During Germination and Stress Response“

Abstract

Hormones regulate plant growth and development, and allow for these sessile organisms to effectively sense changes in their environment. Complex hormone crosstalk networks modulate plant response to endogenous signals and external stressors. A well-known instance of crosstalk occurs between the two antagonistic hormones gibberellin (GA) and abscisic acid (ABA) during developmental phase transitions and unfavourable growth conditions. XERICO (XER) is a DELLA-induced putative RING E3 ubiquitin ligase that increases intracellular ABA levels through a yet unexplored molecular mechanism. The aim of my research is to understand the role of XER in GA-ABA crosstalk during stress response and germination, a phase transition that is tightly regulated to ensure seedling survival. To this end, putative XER substrates have been identified via a high-throughput yeast two-hybrid screen using a cDNA library of genes differentially regulated by ABA. I have also isolated potential upstream regulators from an Arabidopsis transcription factor library using a yeast one-hybrid approach. Preliminary data suggests that XER expression is regulated by stress-responsive transcription factors and that XER may modulate enzymes involved in hormone metabolism. Furthermore, as a crucial step in understanding the role of XER in planta, I analyzed its subcellular localization by tagging it with fluorescent proteins. Transient assays indicate that this protein is targeted to the cytoplasm, chloroplast envelope and possibly to other organelles. In addition, I have generated constitutive and inducible overexpression lines to study its function at the molecular level in future experiments. This project will provide important insight as to how a chloroplast-localized E3 ligase integrates the GA and ABA signaling pathways, and how plants maintain a delicate balance between growth and development to promote survival during instances of environmental stress.