Date of Award

Spring 2019

Document Type

Dissertation - Restricted

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

First Advisor

Schlappi, Michael

Abstract

Rice (Oryza sativa L.) has a sub-tropically origin and is sensitive to low-temperature stress at the young seedling stage. Very few effector genes that code enzymes involved in low-temperature stress response mechanisms have been identified so far. Here, we report a genome-wide association study (GWAS) mapping and a Bi-parental Quantitative Trait Loci (QTL) mapping using 202 O. sativa accessions from the Rice Mini-Core (RMC) collection, which uncovered 48 QTL across all 12 rice chromosomes associated with five chilling tolerance indices. In addition, we characterized qLTSS4-1, a novel strong-effect low-temperature seedling survivability (LTSS) QTL and its associated gene, Os04g24110, which is annotated to encode the UDP-glycosyltransferase enzyme UGT90A1. In rice and Arabidopsis, this gene was cold induced and could significantly reduce electrolyte leakage (EL) to protect cellular membrane integrity during low-temperature stress. Therefore, we re-named the gene ELECTROLYTE LEAKAGE TOLERANCE 1 (ELT1). ELT1 functions as a low-temperature stress tolerance gene in both rice and Arabidopsis by lowering the level of stress-induced reactive oxygen species due to increased antioxidant enzyme activities. Overexpression of ELT1 in Arabidopsis also improved salt stress tolerance of transgenic lines by enhancing antioxidant enzyme activities. Haplotype differences in the promoter of ELT1 leading to significantly higher expression levels in chilling tolerant JAPONICA than chilling sensitive INDICA accessions rather than differences in protein sequences were correlated with the chilling tolerant phenotype. Thus, we propose that high level ELT1 expression is a general responsive mechanism to help maintain cell membrane integrity and reduce oxidative damage during abiotic stresses. This study advanced the understanding of responsive mechanism to abiotic stresses in plants and can be utilized in agricultural applications.

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