Molecular And Physiological Studies On Hst,A Heat-Shock Tolerance Mutant Of Rice(Oryza Sativa L.)

Heat stress has become one of the main factors that lead to a decrease in crops yields, heat tolerance crop varieties are the most effective way to reduce the damage of heat stress. Heat stress can cause osmotic and oxidative stress. Stomata optimize water use efficiency, thereby playing crucial roles in response to abiotic stress.Here, a heat-shock tolerance (hst) mutant was isolated from T7generation of Zhonghua11(ZH11) T-DNA insertion lines. When treated with13-h light (42℃)/11-h dark (37℃) photoperiod and30%relative humidity, the hst mutants exhibited less severe wilting than wild-type (ZH11) plants. Furthermore, the hst mutants showed better recovery than wild-type plants after heat stress. Since the stomatal conductance and stomatal density of the hst mutant was significantly low than wild-type plants, Under heat stress, the hst mutants lost less water and maintained higher water content than wild-type plants. the hst mutant can resist water loss stress caused by high temperature stress to survival after long recovery periods.Genetic analysis revealed that the mutation was controlled by a single recessive gene. PCR analysis and hygromycin resistance assay showed that the mutation was not caused by T-DNA insertion. Since the phenotype of hst mutant is similar with dst mutant in the study of Huang et al.(2009), sequencing of the DST locus from hst mutants showed that four nucleotide insertions at zinc finger domain lead to frame-shift mutation. Loss of DST function increases stomatal closure due to the accumulation of H2O2, consequently resulting in enhanced heat tolerance. Moreover, OsHsfA4a are up-regulated as a result of high accumulation of H2O2. Hence, OsHsfA4a may be an important sensor of H2O2. These finding provide an important genetic engineering approach for improving abiotic stress tolerance in crops.