Emerging roles of plant transcriptional gene silencing under heat.

SUMMARY: Plants continuously endure unpredictable environmental fluctuations that upset their physiology, with stressful conditions negatively impacting yield and survival. As a contemporary threat of rapid progression, global warming has become one of the most menacing ecological challenges. Thus, understanding how plants integrate and respond to elevated temperatures is crucial for ensuring future crop productivity and furthering our knowledge of historical environmental acclimation and adaptation. While the canonical heat‐shock response and thermomorphogenesis have been extensively studied, evidence increasingly highlights the critical role of regulatory epigenetic mechanisms. Among these, the involvement under heat of heterochromatic suppression mediated by transcriptional gene silencing (TGS) remains the least understood. TGS refers to a multilayered metabolic machinery largely responsible for the epigenetic silencing of invasive parasitic nucleic acids and the maintenance of parental imprints. Its molecular effectors include DNA methylation, histone variants and their post‐translational modifications, and chromatin packing and remodeling. This work focuses on both established and emerging insights into the contribution of TGS to the physiology of plants under stressful high temperatures. We summarized potential roles of constitutive and facultative heterochromatin as well as the most impactful regulatory genes, highlighting events where the loss of epigenetic suppression has not yet been associated with corresponding changes in epigenetic marks. Significance Statement: High temperatures pose a major threat to plant physiology. While research has extensively focused on thermomorphogenesis and heat‐shock stress responses, the roles of epigenetic mechanisms remain relatively under‐explored. In particular, the contribution of transcriptional gene silencing (TGS) is probably the least studied. Our review highlights how canonical TGS and heterochromatin dynamics may contribute to plant heat tolerance, summarizing both established and novel insights. With this work, we aim to promote alternative avenues for eventually developing heat‐resistant crops, ultimately contributing to more sustainable agriculture under a global warming scenario. [ABSTRACT FROM AUTHOR]