Abstract Jasmonate (JA) accumulation and signaling play key roles in regulating plant growth and flower development. The optimal timing of flowering is critical for the quality and yield of Brassica juncea. B-box (BBX) factors play roles in plant floral transition and stress response processes. However, whether BBX6-2 responds to JA signaling to regulate flowering time in B. juncea remains unclear. Here, we characterized the biological function of BjuBBX6-2 in response to JA in regulating the flowering time of B. juncea. Subcellular localization and transcriptional activation activity assays showed that BjuBBX6-2 localizes in the nucleus and exhibits transcriptional activation activity. Spraying BjuBBX6-2-overexpressing or -silenced B. juncea plants with 50 μmol/L methyl JA significantly accelerated or delayed their flowering time, respectively. We demonstrated that BjuBBX6-2 interacts with the flowering factor Nuclear Factor Y, Subunit C4 (BjuNF-YC4), which interacts with Nuclear Factor Y, Subunit B2/3 (BjuNF-YB2/3). The BjuBBX6-2–BjuNF-YC4–BjuNF-YB2/3 multiple-protein complex bound to the promoter of the downstream flowering integrator gene SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (BjuSOC1) and promoted its expression. JASMONATE ZIM-DOMAIN 1 (BjuJAZ1), a key factor in the JA signaling pathway, interacted with BjuBBX6-2 to inhibit the activation of BjuSOC1 by BjuBBX6-2. In summary, BjuBBX6-2 cooperates with BjuNF-YC4 and BjuJAZ1 in response to JA signaling to participate in the flowering regulation of B. juncea. These findings highlight a previously uncharacterized mechanism of JA signaling–mediated flowering-time regulation via interactions between BjuBBX6-2 and the integrator gene BjuSOC1, providing prospects for breeding enhanced B. juncea cultivars.
Feng et al. (Sat,) studied this question.