Comparative Transcriptomics Analysis and Functional Study Reveal Important Role of High-Temperature Stress Response Gene GmHSFA2 During Flower Bud Development of CMS-Based F1 in Soybean

High-temperature (HT) is one of the most important environmental factors that negatively impact the yield of some soybean cytoplasmic male sterility (CMS)-based hybrid (F 1 ) combinations. The response of soybean to HT, especially at the male organ development stage, is poorly understood. To investigate the molecular mechanisms of the response from soybean CMS-based F 1 male organ to HT, a detailed transcriptomics analysis was performed during flower bud development of soybean HT-tolerant and HT-sensitive CMS-based F 1 combinations (NF 1 and YF 1 ) under normal-temperature and HT conditions. Obvious HT damage was observed by subjecting YF 1 with HT, such as indehiscent anthers and decreased pollen fertility, whereas the male fertility of NF 1 was normal. In total, 8,784 differentially expressed genes (DEGs) were found to respond to HT stress, which were mainly associated with anther/pollen wall development, carbohydrate metabolism and sugar transport, and auxin signaling. The quantitative real-time PCR (qRT-PCR) analysis and substance content detection also revealed that HT caused male fertility defects in YF 1 by altering pectin metabolism, auxin, and sugar signaling pathways. Most importantly, the sugar signaling- PIF -auxin signaling pathway may underlie the instability of male fertility in YF 1 under HT. Furthermore, HT induced the expression of heat shock factor ( HSF ) and heat shock protein ( HSP ) gene families. Overexpression of GmHSFA2 in Arabidopsis can promote the expression of HT protective genes (such as HSP20 ) by binding to the HSE motifs in their promoters, so as to improve the HT tolerance during flowering. Our results indicated that GmHSFA2 acted as a positive regulator, conferring HT tolerance improvement in soybean CMS-based F 1 . GmHSFA2 may be directly involved in the activation of male fertility protection mechanism in the soybean CMS-based F 1 under HT stress.