MBAPs link brassinosteroid signaling and cortical microtubules

Abstract:

Cell surface receptors are essential for sensing a broad range of exogenous and endogenous signals. In plants, receptor-like kinase families play crucial roles in such processes, but the whole picture of the downstream pathways remains unclear, particularly with respect to non-transcriptional responses. Our team focuses on BRASSINOSTEROID INSENSITIVE 1 (BRI1), a major brassinosteroid (BR) receptor, as a representative model to unveil the downstream mechanisms of receptor signaling at the cell surface.

Recently, we identified several novel interactors of the BRI1 cytosolic domain through a Y2H screen. Among them, MBAPs (MICROTUBULE-BRI1 ASSOCIATED PROTEINs), localize to cortical microtubules, and, to be noteworthy, BiFC data implied that MBAPs and some population of BRI1 interact on cortical microtubules. Physiologically, MBAPs act as negative regulators of BR-mediated hypocotyl cell elongation, most likely by suppressing BR-triggered microtubule reorientation, rather than through the canonical transcriptional pathway.

Besides regulating microtubules during responses to BRs, MBAPs also play critical roles in microtubule organization. Despite normal growth, the microtubule orientation in mbap mutants is significantly disordered, suggesting MBAPs also mediate tension-microtubule feedback. To further investigate this independent function of BRI1 signaling, we focus on Marchantia polymorpha as a model since its genome encodes an MBAP gene, but not BRI1 homologs. We have confirmed the Marchantia homolog also localizes to microtubules and severely affects their growth. In this presentation, I will also discuss the roles of MBAP in microtubule regulation in Marchantia.

References

Delesalle et al. (2026) Plant communications (Doi : 10.1016/j.xplc.2025.101637)

Delesalle et el. (2024) Nature Plants (Doi : 10.1038/s41477-024-01621-2)