PhD transfer seminar – Jenan Noureddine (Zhao Lab)

Molecular mechanism of ER-localized HSP90 family chaperone in modulating auxin-mediated plant development and stress response

Abstract

ER-localized HSP90 family chaperone is required for protein secretion and has been reported to regulate shoot and root apical meristem maintenance in plant Arabidopsis thaliana. In an RNA sequencing study, we found that reduced expression of ER-localized HSP90.7 results in repression of Arabidopsis genes in the auxin responsive pathway. Auxin is primarily synthesized via tryptophan-dependent pathways and participates in almost every aspect of the cellular processes. meristem cell differentiations. To better understand the role of HSP90.7 in auxin homeostasis, I investigated how expression of representative auxin related marker proteins were impacted in the knockout hsp90.7 line. Preliminary data suggests a suppression of PIN4GFP and significant increase in IAA2GUS, ASA1GUS, and ASB1GUS expression in the root tissues of hsp90.7 mutant. I also observed defective root and shoot development for the mutant at the early seedling stage. I am proposing to further investigate how the biogenesis and turnover of both plasma membrane and ER-localized auxin carrier PIN proteins are affected in the mutant. Additionally, expression patterns of representative CLAVATA-WUSCHEL pathway proteins in controlling the root and shoot meristem maintenance will be analyzed. I will also construct and analyze HSP90.7 truncation mutant lines and investigate how HSP90.7 potentially interact and regulate its candidate client proteins in normal and abiotic stress conditions. It is anticipated that this study will shed light on the mechanism of ER HSP90 family molecular chaperone in regulating cellular auxin homeostasis and involvement in the maintenance of root and shoot apical meristem in Arabidopsis.