High temperature at anthesis is one of the most serious stress factors for rice (Oryza sativa L.) production, causing irreversible yield losses and reduces grain quality. Illustration of thermotolerance mechanism is of great importance to accelerate rice breeding aimed at thermotolerance improvement. Here, we identified a new thermotolerant germplasm, SDWG005. Microscopical analysis found that stable anther structure of SDWG005 under stress may contribute to its thermotolerance. Dynamic transcriptomic analysis totally identified 3559 differentially expressed genes (DEGs) in SDWG005 anthers at anthesis under heat treatments, including 477, 869, 2335, and 2210 for 1, 2, 6, and 12 h, respectively; however, only 131 were regulated across all four-time-points. The DEGs were divided into nine clusters according to their expressions in these heat treatments. Further analysis indicated that some main gene categories involved in heat-response of SDWG005 anthers, such as transcription factors, nucleic acid and protein metabolisms related genes, etc. Comparison with previous studies indicates that a core gene-set may exist for thermotolerance mechanism. Expression and polymorphic analysis of agmatine-coumarin-acyltransferase gene OsACT in different accessions suggested that it may involve in SDWG005 thermotolerance. This study improves our understanding of thermotolerance mechanisms in rice anthers during anthesis, and also lays foundation for breeding thermotolerant varieties via molecular breeding.

Extreme hot weather severely limits rice (Oryza sativa) production. Rice cultivars from regions with hot weather are a valuable resource for breeding heat-tolerant rice, but the mechanisms mediating heat tolerance in these cultivars are not fully understood. Here, we investigated heat-tolerance mechanisms in rice using the well-known heat-tolerant cultivar Nagina 22 (N22) and comparing it with the less heat-tolerant cultivar 93–11. Following heat shock (HS) treatment (45 °C for 3 or 24 h), the expression of JASMONATE ZIM-DOMAIN (JAZ) genes spiked during the early stages of HS responses in N22 but not 93–11 and genes related to jasmonic acid (JA) signaling were repressed in N22. Promoting JA signaling in N22 via pretreatment with methyl JA (MeJA) impaired the heat tolerance of N22, measured as survival after HS treatment of 45 °C for 30 h, followed by a 7-d recovery. Furthermore, the N22-specific activation of JAZ genes was associated with increased histone acetylation and decreased DNA methylation. Comparing N22 to 93–11, we propose that the DNA demethylation process, rather than the hypomethylation status per se, is likely associated with JAZ activation. In summary, we revealed epigenetic mechanisms that may contribute to the heat tolerance of N22 via the JA signaling pathway; our findings have implications for improving heat tolerance in rice and other crops.

In this study, based on the OneKP database and through comparative genetic analysis, we found that HMT and HDM may originate from Chromista and are highly conserved in green plants, and that during the evolution from algae to land plants, histone methylation modifications gradually became complex and diverse, which is more conducive to the adaptation of plants to complex and variable environments. We also characterized the number of members, genetic similarity, and phylogeny of HMT and HDM families in barley using the barley pangenome and the Tibetan Lasa Goumang genome. The results showed that HMT and HDM were highly conserved in the domestication of barley, but there were some differences in the Lasa Goumang SDG subfamily. Expression analysis showed that HvHMTs and HvHDMs were highly expressed in specific tissues and had complex expression patterns under multiple stress treatments. In summary, the amplification and variation of HMT and HDM facilitate plant adaptation to complex terrestrial environments, while they are highly conserved in barley and play an important role in barley growth and development with abiotic stresses. In brief, our findings provide a novel perspective on the origin and evolutionary history of plant HvHMTs and HvHDMs, and lay a foundation for further investigation of their functions in barley.