Genome-Wide Characterization and Expression Analysis of Heat Shock Transcription Factors in Two Cultivars of Rice (Oryza sativa L.) Under Heat Stress

Rising temperatures pose daunting challenges for sustainable yield and nutritional quality of rice (Oryza sativa L.), thus putting food security at risk. Limited information exists regarding cis-acting regulatory elements and candidate genes controlling the heat shock transcription factor (HSF) gene family in rice. Therefore, the present study identified HSF genes in the japonica (Nipponbare) and indica (9311) rice cultivars through in silico repositories. Three candidate genes (HSFC2B, HSFB1, and HSFC2A) were selected for qRT-PCR analysis to validate their expression patterns under heat stress (HS). The present findings reported a total of 25 OsHSF genes through in silico genome-wide identification. Comparative analysis illustrated that the OsHSF genes had structural similarities but different expression and transcriptional regulation between the two cultivars. HSF genes were unevenly distributed across the 12 rice chromosomes, suggesting that tandem duplication and gene repetition may have contributed to the evolution of novel genes. Phylogenetic analysis revealed that all OsHSF gene family members have shared common ancestry, but several genes lack introns, potentially facilitating swift stress responses as indicated by gene structure analysis. Expression analysis revealed that candidate genes were active, with HSFC2A exhibiting the highest level of expression in the japonica cultivar compared to indica under heat-stressed conditions. HSFC2B gene showed a higher statistical difference in its response between cultivars, time points, and cultivar vs. time points interactions compared to HSFC2A and HSFB1. These findings offer valuable insights into the function of OsHSF genes that will contribute to the development of climate-resilient rice cultivars.