The m6A reader SiYTH1 enhances drought tolerance by affecting the messenger RNA stability of genes related to stomatal closure and reactive oxygen species scavenging in Setaria italica

Abstract

Foxtail millet (Setaria italica), a vital drought-resistant crop, plays a significant role in ensuring food and nutritional security. However, its drought resistance mechanism is not fully understood. N⁶-methyladenosine (m⁶A) modification of RNA, a prevalent epi-transcriptomic modification in eukaryotes, provides a binding site for m⁶A readers and affects plant growth and stress responses by regulating RNA metabolism. In this study, we unveiled that the YT521-B homology (YTH) family gene SiYTH1 positively regulated the drought tolerance of foxtail millet. Notably, the siyth1 mutant exhibited reduced stomatal closure and augmented accumulation of excessive H₂O₂ under drought stress. Further investigations demonstrated that SiYTH1 positively regulated the transcripts harboring m⁶A modification related to stomatal closure and reactive oxygen species (ROS) scavenging under drought stress. SiYTH1 was uniformly distributed in the cytoplasm of SiYTH1-GFP transgenic foxtail millet. It formed dynamic liquid-like SiYTH1 cytosol condensates in response to drought stress. Moreover, the cytoplasmic protein SiYTH1 was identified as a distinct m⁶A reader, facilitating the stabilization of its directly bound SiARDP and ROS scavenging-related transcripts under drought stress. Furthermore, natural variation analysis revealed SiYTH1^AGTG as the dominant allele responsible for drought tolerance in foxtail millet. Collectively, this study provides novel insights into the intricate mechanism of m⁶A reader-mediated drought tolerance and presents a valuable genetic resource for improving drought tolerance in foxtail millet breeding.