GLABRA3-mediated trichome branching requires transcriptional repression of MICROTUBULE-DESTABILIZING PROTEIN25

Microtubules play pivotal roles in establishing trichome branching patterns, which is a model system for studying cell-shape control in Arabidopsis (Arabidopsis thaliana). However, the signaling pathway that regulates microtubule reorganization during trichome branching remains poorly understood. In this study, we report that MICROTUBULE-DESTABILIZING PROTEIN25 (MDP25) is involved in GLABRA3 (GL3)-mediated trichome branching by regulating microtubule stability. Loss of MDP25 function led to excessive trichome branching, and this phenotype in mdp25 could not be rescued by the MDP25 K7A or MDP25 K18A mutated variants. Pharmacological treatment and live-cell imaging revealed increased microtubule stability in the mdp25 mutant. Furthermore, the microtubule collar observed during trichome branching remained more intact in mdp25 compared to the WT under oryzalin treatment. Results of genetic assays further demonstrated that knocking out MDP25 rescued the reduced branching phenotype of gl3 trichomes. In gl3 trichomes, normal microtubule organization was disrupted, and microtubule stability was significantly compromised. Moreover, GL3 physically bound to the MDP25 promoter, thereby inhibiting its expression. Overexpression of GL3 negated the effects of PMDP25-driven MDP25 or its mutant proteins on trichome branching and microtubules in the mdp25 background. Overall, our study uncovers a mechanism by which GL3 inhibits MDP25 transcription, thereby influencing microtubule stability and regulating trichome branching. This mechanism provides a connection between early regulatory components and microtubules during trichome development.