Genome-wide analysis of the Hsp70 gene family in rice reveals that OsHsp70-9 plays a significant role in heat stress response

Heat shock protein 70 (Hsp70) is a key molecular chaperone in plant stress responses playing a crucial role in maintaining growth homeostasis under heat stress. In this study, we revealed the evolutionary conservation of the OsHsp70 family through phylogenetic tree construction, collinearity analysis, and Ka/Ks analysis. We also screened the heat-tolerance candidate genes using various methods, including tissue-specific expression analysis, expression profiling under heat stress, haplotype analysis of heat-tolerance indicators in 620 rice germplasms, amino acid site mutation, and RT-qPCR. The results showed that the promoter regions of Hsp70 genes contained multiple cis-acting elements related to stress responses. Seven pairs of intragenic collinear genes were identified in OsHsp70s, and Ka/Ks analysis indicated that this family has undergone strong purifying selection. Expression analysis showed that most OsHsp70 genes have tissue-specific expression. Haplotype analysis indicated that the Hap2 of OsHsp70-9 plays an important role in the heat-stress tolerance of rice, and a non-synonymous mutation of OsHsp70-9 led to changes in the domain. RT-qPCR analysis showed that the expression of OsHsp70-9 varied significantly under heat stress, which is consistent with the expression profiling results under heat stress. Overall, this study demonstrates that Hsp70 genes play a potential role in the stress tolerance of rice, and provides important clues for better understanding the molecular mechanisms underlying the adaptation of rice to environmental changes and the adaptive evolution of Hsp70 genes.