Four R2R3-MYB subgroup 13 transcription factors regulate silique dehiscence and secondary cell wall synthesis in Arabidopsis thaliana.

Silique dehiscence is an important agronomic trait in oilseed Brassicaceae crops, including canola, mustard, and camelina, yet its molecular regulation remains incompletely understood. Here, we show that four R2R3-MYB subgroup 13 transcription factors-MYB55, MYB61, MYB50, and MYB86-function redundantly to regulate silique dehiscence and secondary cell wall (SCW) biosynthesis in Arabidopsis thaliana. Simultaneous knockout of these four genes caused severe stem lodging and loss of interfascicular fibers in inflorescence stems, accompanied by strong downregulation of genes involved in cellulose, hemicellulose, and lignin biosynthesis, which are directly activated by these MYBs. In addition to SCW defects, the myb55/61/50/86 quadruple mutant displayed enhanced silique dehiscence. Mechanistically, these MYBs repress the expression of ADPG1, encoding a polygalacturonase that promotes dehiscence by mediating pectin degradation in the valve margin separation layer. Loss of MYB function resulted in elevated ADPG1 expression and increased dehiscence, whereas mutation of ADPG1 in the myb55/61/50/86 background suppressed the phenotype and reduced dehiscence to approximately wild-type levels. Together, our results refine the regulatory network controlling SCW biosynthesis and reveal a previously unrecognized MYB-dependent pathway that modulates silique dehiscence.