PhD Transfer Seminar – Saad Hussain (Nambara Lab)

Abstract

Plants use a variety of mechanisms to adapt to their environmental conditions such as changes in water availability. This adaptation is mediated by the phytohormone abscisic acid (ABA). When plants face increases in water availability such as high relative humidity (RH) or flooding/submergence conditions, they have to reduce endogenous ABA levels through ABA catabolism. Conversely, when faced with drought stress and low RH, ABA levels increase due to upregulation of the ABA biosynthesis gene 9-cis-epoxycarotenoid dioxygenase 3 (NCED3). ABA is catabolized in Arabidopsis by the CYP707A gene family which encodes for ABA 8’-hydroxylases. CYP707A3 is involved in catabolizing ABA during short-term high RH, allowing for stomatal opening and transpiration to occur. Early induction of CYP707A3 during high RH treatment for one hour is correlated with a decline in endogenous ABA levels. In cyp707a3 mutants, plants have increased stomatal apertures and higher ABA levels than wild-type plants. Key questions about transcriptional regulators and gene regulatory networks that work with CYP707A3 during high RH still remain unanswered. In the present study, we have investigated high humidity-induced transcriptional regulation of CYP707A3 via identification of cis-element(s) and transcription factors (TF) involved in this regulation. We developed a short-term high RH assay that was able to replicate the decline in ABA levels after one hour of high RH seen previously. By utilizing this system, our results show that during short-term high RH, calmodulin binding transcription activator (CAMTA) double mutants camta1camta2 and camta1camta3 displayed a similar phenotype to that of cyp707a3 mutants with ABA levels being similar to those of plants tested before the onset of high RH treatment. CAMTA TFs are involved in a variety of environmental responses and CAMTA1 has been reported to bind to the DNA consensus sequence 5′-[ACG]CGCG[GTC]-3 on the CYP707A3 promoter. These results suggest that CAMTA TFs along with CYP707A3 have a role in short-term high RH responses. Based on these findings, my research will focus on locating a high humidity responsive element (HHRE) on the promoter of CYP707A3 and determine whether CAMTA1 binds to this HHRE. I will also characterize CAMTA1activity during high RH by studying gene expression and subcellular localization. Additionally, our results showed CYP707A3 promoter activity under submergence using a GUS reporter system. I will be researching if CYP707A3 is responsible for submergence induced ABA decline. Finally, I will determine whether NCED3 mediated ABA biosynthesis is responsible for low RH responses.

https://utoronto.zoom.us/j/87259607243

Meeting ID: 872 5960 7243
Host: Eiji Nambara (eiji.nambara@utoronto.ca)