ETHYLENE RESPONSE FACTOR 070 inhibits flowering in Pak-choi by indirectly impairing BcLEAFY expression

Abstract APETALA2/ethylene responsive factors respond to ethylene and participate in many biological and physiological processes, such as plant morphogenesis, stress resistance, and hormone signal transduction. Ethylene responsive factor 070 (BcERF070) is important in flowering. However, the underlying molecular mechanisms of BcERF070 in floral transition in response to ethylene signaling have not been fully characterized. Herein, we explored the function of BcERF070 in Pak-choi [Brassica campestris (syn. Brassica rapa) ssp. chinensis]. Ethylene treatment induced BcERF070 expression and delayed flowering in Pak-choi. Silencing of BcERF070 induced flowering in Pak-choi. BcERF070 interacted with major latex protein-like 328 (BcMLP328), which forms a complex with helix-loop-helix protein 30 (BcbHLH30) to enhance the transcriptional activity of BcbHLH30 on LEAFY (BcLFY), ultimately promoting flowering. However, BcERF070 impaired the BcMLP328–BcbHLH30 complex activation of LEAFY (BcLFY), ultimately inhibiting flowering in Pak-choi. BcERF070 directly promoted the expression of the flowering inhibitor gene B-box 29 (BcBBX29) and delayed flowering by reducing FLOWERING LOCUS T (BcFT) expression. These results suggest that BcERF070 mediates ethylene-reduced flowering by impairing the BcMLP328–BcbHLH30 complex activation of BcLFY and by directly promoting the gene expression of the flowering inhibition factor BcBBX29 to repress BcFT expression. The findings contribute to understanding the molecular mechanisms underlying floral transition in response to ethylene in plants.