All ETDs from UAB

Advisory Committee Chair

Karolina M Mukhtar

Advisory Committee Members

Steven N Austad

Shahid M Mukhtar

Mohammad Athar

Aaron M Rashotte

Document Type

Dissertation

Date of Award

2017

Degree Name by School

Doctor of Philosophy (PhD) College of Arts and Sciences

Abstract

Plants are capable of recognizing conserved molecular structures from pathogens and precisely regulates gene expression to establish effective and efficient immune responses. Transcriptional regulation has been extensively characterized in plant immunity, while relatively less is understood on the translational level. Moreover, switching cellular energy from growth- to defense-related activity may result in the buildup of misfolded or unfolded proteins within the endoplasmic reticulum (ER), and activating the unfolded protein response (UPR) is critical for restoringllular homeostasis. My dissertation is set out to understand the function of translational regulatory mechanism and UPR in plant immune responses. As a key transcriptional regulator for plant growth-to-defense transition, TBF1, is translationally regulated through the upstream open reading frames (uORFs). My research demonstrated that AtGCN2-eIF2α is indispensable for TBF1 translational regulation. Under steady states, TBF1 translation is inhibited by the uORFs. However, pathogen challenge quickly activates AtGCN2-dependent eIF2α phosphorylation, and the phosphorylated eIF2α allows translation reinitiation at the main ORF (mORF). Besides functioning in seed germination and plant development, AtGCN2 controls plant immunity during pre-invasive stage by controlling the stomatal aperture in response to microbe-associated molecular patterns (MAMPs) and phytotoxin coronatine. AtGCN2 also plays an essential role in modulating the phytohormone abscisic acid (ABA) accumulation and signaling cascade to control plant immunity during post-invasive stage. Those findings elaborated the critical role of translational regulator AtGCN2 in fine-tuning the plant immune response. Besides regulating translation of mRNA, the newly synthesized peptides are closely monitored by the ER stress sensor AtIRE1. Upon activation, AtIRE1 splices AtbZIP60 mRNA to produce a functional transcription factor for inducing the expression of ER-resident genes. However, the function of AtIRE1-AtbZIP60 pathway in cell fate decision upon biotic stress remains unclear. My analyses revealed that AtIRE1-AtbZIP60 inhibits cell death transition upon the perception of avirulent pathogen. Furthermore, AtIRE1a interacts with a well conserved cell death suppressor AtBI-1 and this interaction is tightly regulated by the phosphorylation status of two amino acids. In summary, my dissertation unrevealed the critical function of two conserved stress sensors AtGCN2 and AtIRE1 in regulating plant immune response and executing cell fate decision.

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