Differential Drought Responses in F-box Gene Expression and Grain Yield Between Two Rice Groups with Contrasting Drought Tolerance

Understanding the molecular mechanisms regulating rice’s response to drought stress is important for cereal crop development. We investigated the physiological and gene expression responses of three drought-tolerant and two drought-sensitive unrelated rice cultivars at the reproductive stage. Leaf water loss and leaf rolling tests distinguished these two groups from each other. Both 7 and 14 days of drought stress affected most of the tested agronomic traits including grain yield, and the effects were stronger in the drought-sensitive cultivars. Fourteen days of drought stress severely reduced grain yield in the sensitive cultivars. Expression levels of 50 genes previously published were examined in panicles. Of these, 25 genes were expressed in panicles and could be classified into 6 groups. LOC_Os02g51350, a Kelch domain-containing F-box gene, was selected for further studies including expression analysis in panicles during the 14-day drought stress, domain analysis, and analysis of cis-acting elements in the promoters. All three drought-resistant cultivars possessed the F-box domain, which was absent in the two drought-sensitive cultivars. In addition, drought-related ABRE and DRE/CRT cis-acting elements were more abundant in Os02g51350 promoters of cultivars with good grain yield under drought stress than in promoters of cultivars with severe yield reduction. Our results suggest that the F-box version of Os02g51350 is important for maintenance of grain yield under drought.