Characterization of candidate genes for ozone tolerance in winter wheat (Triticum aestivum L.) and associated physiological mechanisms

Rising tropospheric ozone causes global yield reduction in wheat and therefore necessitates the breeding of ozone-resistant wheat varieties. The aim of this study was to explore contrasting physiological responses and characterize candidate genes for ozone tolerance in wheat identified in a genome-wide association study. Four wheat genotypes were grouped into tolerant and sensitive haplotypes according to their genetic backgrounds at ozone tolerant loci, and were investigated under season-long ozone fumigation in open-top chambers. Only sensitive haplotypes showed a significant decrease in net photosynthetic rate and a significant increase in lipid peroxidation indicating oxidative stress. Moreover, tolerant and sensitive haplotypes of wheat showed consis-tently contrasting antioxidant responses to ozone in terms of apoplastic ascorbate, ascorbate peroxidase and peroxidase activity. Candidate genes located within an ozone tolerant locus on chromosome 5A 592.04-593.33 Mb were analyzed through gene expression. The gene TraesCS5A01G400500 putatively involved in peroxidase activity was only upregulated in tolerant haplotypes. The differential regulation was consistent with sequence polymorphisms in the promoter region, where the cis-elements, EVENINGAT and PREATPRODH were only present in tolerant haplotypes. Based on the consistency of differential expression and sequence polymorphisms between tolerant and sensitive haplotypes, TraesCS5A01G400500 might explain contrasting physiological re-sponses after ozone fumigation. This study demonstrated consistent transcriptional regulation, sequence poly-morphisms in a candidate gene and physiological responses to ozone in different haplotypes, which represents a step forward in the understanding of the molecular mechanism underlying ozone tolerance in wheat.