The BES1–KCS1 regulatory module suppresses callus formation through coordinated crosstalk between BR signaling and VLCFA biosynthesis

The induction of pluripotent callus from somatic cells is a key step in plant regeneration, with broad implications for developmental biology, biotechnology, and crop genetic improvement. While the association between auxin and cytokinin is well established as the central regulator of regeneration programs, the roles of other phytohormones remain poorly understood. Here, we elucidate a mechanism by which the brassinosteroid (BR) signaling transcription factor BES1 negatively regulates callus formation by modulating very-long-chain fatty acid (VLCFA) biosynthesis in Arabidopsis and cotton. AtBES1 directly binds to BR response elements (BRREs) in the promoter region of AtKCS1 , which encodes a rate-limiting enzyme in VLCFA biosynthesis, thereby enhancing AtKCS1 expression and elevating endogenous VLCFA levels. Functional analyses using Atkcs1 and Ghkcs1 knockout mutants revealed a marked increase in callus formation, confirming the conserved negative regulatory role of KCS1 in this process. Genetic analyses further demonstrated that KCS1 functions epistatically to BES1 within this pathway. Collectively, these findings uncover an uncharacterized regulatory module in which BR signaling and VLCFA metabolism converge to repress callus formation, offering new insights into the lipid–hormone crosstalk governing cellular pluripotency during plant regeneration.