Epigenetic-epitranscriptomic crosstalk through TaHAG1-TaNSUN2 coordinates thermotolerance in wheat.

Abstract

High temperature is a primary abiotic stress that severely constrains crop productivity. Deciphering the regulatory pathways underlying heat responses is essential for breeding heat-tolerant crops with stable yields. Although both epigenetic and epitranscriptomic regulations are involved in plant heat adaptation, their mechanistic interplay remains unclear. Here, integrated epigenomic (H3K9Ac/H3K14Ac) and transcriptomic profiling under heat stress identifies the mRNA m⁵C methyltransferase TaNSUN2 as a key regulator of thermotolerance in wheat. We demonstrate that TaNSUN2 is transcriptionally activated by the histone acetyltransferase TaHAG1, which deposits H3K9Ac at the TaNSUN2 promoter and transcription start site. This recruitment is facilitated by the transcription factors TaE2F1 and TaDP1, which interact with TaHAG1 to form a functional complex. Functional assays revealthat TaNSUN2 operates downstream of TaHAG1 and enhances thermotolerance through m⁵C‑dependent mRNA methylation and stabilization of transcripts involved in chloroplast organization. Furthermore, field trials show that TaNSUN2-overexpressing lines exhibit higher grain yield under normal conditions and reduced yield loss under heat stress. Our findings elucidate an integrated regulatory network linking histone acetylation to RNA m⁵C methylation in heat stress adaptation, providing promising targets for molecular breeding of heat‑resilient wheat.