BjuABI4 and BjuJAZ2 respond to ABA signals and antagonistically regulate flowering time in Brassica juncea

Flowering time is a fundamental agronomic trait determining the adaptation and yield of Chinese mustard (Brassica juncea), an important industrial crop widely cultivated in southwestern China as the main raw material for the pickled vegetable processing industry. ABSCISIC ACID-INSENSITIVE 4 (ABI4) is a key component of abscisic acid (ABA) signaling involved in plant development and stress responses, yet how it mediates flowering time control in Brassica juncea remains largely unknown. Here, we identify BjuABI4 as a negative regulator of flowering that directly activates the floral repressor BjuFLC in Brassica juncea. Intriguingly, this activation is antagonized by BjuJAZ2, a core jasmonate signaling component, which physically interacts with BjuABI4 to attenuate its transcriptional activity and alleviate the ABA-induced delayed flowering phenotype. Conversely, BjuPIF3, a key light signaling regulator, cooperates with BjuABI4 to synergistically enhance BjuABI4 and BjuFLC expression and potentiate ABA signal transduction, further delaying flowering. Notably, ABA treatment strengthens the BjuPIF3-BjuABI4 interaction while weakening the BjuJAZ2-BjuABI4 association, creating a dynamic regulatory balance that fine-tunes BjuFLC expression. Functionally, this PIF3-ABI4-JAZ2 module also mediates drought stress adaptation by modulating flowering time under adverse conditions. Our findings delineate a regulatory framework of PIF3-ABI4-JAZ2 and its antagonistic mechanism in mediating flowering time of Brassica juncea, which holds great promise for breeding stress-tolerant industrial crops and enhancing the quality and yield stability of raw materials for vegetable processing.