Rice OsHSFA3 Gene Improves Drought Tolerance by Modulating Polyamine Biosynthesis Depending on Abscisic Acid and ROS Levels

Abstract

Drought is a serious problem, which causes heavy yield losses for rice. Heat-shock factors (HSFs) had been implicated in tolerance to drought and high temperature. However, there has not been much functional characterization and mechanism clarification in rice. Previously, we found an HSF gene, <i>OsHSFA3</i>, was highly related with drought tolerance after screening from 10,000 different samples. Herein, we cloned the <i>OsHSFA3</i> from rice and overexpressed it in <i>Arabidopsis thaliana</i> to study its regulatory mechanism of drought tolerance. Phenotypic and physiological assays of the transgenic <i>Arabidopsis</i> lines showed that overexpression of <i>OsHSFA3</i> confers drought tolerance by reducing water loss and reactive oxygen species (ROS) levels, whereas it increases abscisic acid (ABA) levels. However, enzymatic antioxidants such as activity levels of superoxide dismutase, peroxidase and catalase were not significantly different between wild type and transgenic lines. Instead, we observed a significant increase in polyamine content, which was correlated with increased <i>AtADC1, AtADC2, SPDS1</i> and <i>SPMS</i> expression levels. In silico and in vivo analyses confirmed that <i>OsHSFA3</i> is a nuclear-localized gene. In addition, <i>OsHSFA3</i> can bind to the promoter of <i>AtADC1</i> and <i>OsADC</i> via a yeast one-hybrid assay. Overall, this study reveals that <i>OsHSFA3</i> improves drought tolerance in <i>Arabidopsis</i> not only by increasing ABA levels, but also by modulating polyamine levels to maintain ROS homeostasis, therefore it could be a strong candidate to develop drought-tolerant rice cultivars.