Somatic memory of exogenous brassinosteroids alters histone expression and tempers heat responses

Background Brassinosteroids (BRs) are a class of phytohormones known for enhancing plant resilience to various stresses. BRs influence development via cellular division, differentiation, and elongation across plant tissues throughout both vegetative and reproductive growth. This study examined the effects of a BR seed soak application on wheat ( Triticum aestivum L.) under heat stress, focusing on agronomic traits and gene expression. Results The BR treatment selectively mitigated heat stress effects on spike length and spikelet number without improving grain yield or fertility, highlighting its specific developmental influence. The genotype Vida uniquely maintained spikelet density despite increased spike length, unlike other genotypes, suggesting Vida harbors genetic variation that could reduce yield component trade-offs. RNA-seq analysis in Vida was consistent with the BR treatment priming cell proliferation and altered cell wall production but was not consistent with long-term BR signaling changes. The BR treatment also reduced heat stress-induced gene expression, including heat shock factors (Hsfs) and chaperones, indicating a suppression of the canonical heat stress response. Additionally, BR treatment affected histone gene expression, with many histones upregulated and others protected from heat stress-induced downregulation, suggesting a role in maintaining chromatin stability and somatic stress memory. Conclusions These findings indicate that BR seed soak application partially rescues spike development under heat stress and influences gene regulation, particularly in histone expression. This dual effect points to potential novel strategies for enhancing stress tolerance in wheat through a better understanding of BRs' role in plant development and gene expression.