SOBIR1/EVR prevents precocious initiation of fiber differentiation during wood development through a mechanism involving BP and ERECTA.

Abstract

In plants, secondary growth results in radial expansion of stems and roots, generating large amounts of biomass in the form of wood. Using genome-wide association studies (GWAS)-guided reverse genetics in <i>Arabidopsis thaliana</i>, we discovered <i>SOBIR1/EVR</i>, previously known to control plant immunoresponses and abscission, as a regulator of secondary growth. We present anatomical, genetic, and molecular evidence indicating that SOBIR1/EVR prevents the precocious differentiation of xylem fiber, a key cell type for wood development. SOBIR1/EVR acts through a mechanism that involves BREVIPEDICELLUS (BP) and ERECTA (ER), 2 proteins previously known to regulate xylem fiber development. We demonstrate that BP binds <i>SOBIR1/EVR</i> promoter and that <i>SOBIR1/EVR</i> expression is enhanced in <i>bp</i> mutants, suggesting a direct, negative regulation of BP over <i>SOBIR1/EVR</i> expression. We show that SOBIR1/EVR physically interacts with ER and that defects caused by the <i>sobir1/evr</i> mutation are aggravated by mutating <i>ER</i>, indicating that SOBIR1/EVR and ERECTA act together in the control of the precocious formation of xylem fiber development.