SUB 1 A ‐mediated submergence tolerance response in rice involves differential regulation of the brassinosteroid pathway

S ubmergence 1 A ( SUB 1 A ), is an ethylene response factor ( ERF ) that confers submergence tolerance in rice ( O ryza sativa ) via limiting shoot elongation during the inundation period. SUB 1 A has been proposed to restrict shoot growth by modulating gibberellic acid ( GA ) signaling. Our transcriptome analysis indicated that SUB 1 A differentially regulates genes associated with brassinosteroid ( BR ) synthesis during submergence. Consistent with the gene expression data, the SUB 1 A genotype had higher brassinosteroid levels after submergence compared to the intolerant genotype. Tolerance to submergence can be activated in the intolerant genotype by pretreatment with exogenous brassinolide, which results in restricted shoot elongation during submergence. BR induced a GA catabolic gene, resulting in lower GA levels in SUB 1 A plants. BR treatment also induced the DELLA protein SLR1 , a known repressor of GA responses such as shoot elongation. We propose that BR limits GA levels during submergence in the SUB 1 A rice through a GA catabolic enzyme as part of an early response and may repress GA responses by inducing SLR 1 after several days of submergence. Our results suggest that BR biosynthesis is regulated in a SUB 1 A ‐dependent manner during submergence and is involved in modulating the GA signaling and homeostasis.