Allelic variations and interactive feedback in major regulators of plant architecture confer high‐altitude adaptation in Arabidopsis thaliana

Summary Ideal plant architectures are crucial for adapting to environmental changes, yet the molecular mechanisms behind high‐altitude plant adaptations remain elusive. We characterized the dwarf and highly branched traits of the Tibet ecotype of Arabidopsis thaliana (L.) Heynh. Quantitative trait locus (QTL) analysis revealed that GA5 and BRC1 , as major genes regulating plant height and branching, respectively, underlie the variation in plant architecture of the Tibet ecotype. Loss‐of‐function of GA5 disrupts gibberellin biosynthesis, leading to dwarfism, and natural variations in the BRC1 promoter reduce its expression, promoting branching. A positive feedback loop formed by GA5 and BRC1 via the DELLA‐SPL9 module balances plant height and branching. Additionally, alleles of GA5 and BRC1 exhibit contrasting sensitivity to UV‐B radiation and low temperatures, suggesting that they have experienced strong ecological selections at high altitudes. Our findings reveal that GA5 and BRC1 form a feedback regulatory module that coordinately regulates the balance between plant height and branching, thereby governing developmental adaptation to high‐altitude environments.