Hormone modulates protein dynamics to regulate plant growth

Abstract

Endosomal traffic in the plant endomembrane system is a fundamental and complex process that controls many essential cellular, developmental, and physiological functions in plants, including cellular polarization, cytokinesis, metal ion homeostasis, pathogen defense, and hormone transport (1). The secretory and endocytic pathways represent two major anterograde protein transport routes for protein delivery into the vacuole in plant cells (Fig. 1 A ). In the secretory pathway, transportation of newly synthesized soluble vacuolar cargo proteins is mediated by the vacuolar sorting receptors (VSRs) (2). After delivery of the soluble cargos into an intermediate compartment, receptors are recycled by the attachment of conserved sorting nexins (SNXs) and the core subunits of retromer complex (VPS26, VPS29, and VPS35) to the membrane. Nevertheless, the precise localization of the SNXs and the retromer subunits, as well as the identity of the organelles from which VSRs are recycled, remains in debate (3, 4). During endocytosis, plasma membrane (PM) proteins are internalized and delivered into the trans -Golgi network (TGN)/early endosomes in plants (5). Ubiquitinated PM proteins are further sorted into the intralumenal vesicles of multivesicular bodies, previously identified as a prevacuolar compartment (6), by the endosomal sorting complex required for transport machinery for vacuolar degradation (7). Alternatively, PM proteins without a ubiquitin tag (or after removal of ubiquitin by a deubiquitinating enzyme) are recycled back to the PM from the TGN or recycling endosome (RE) (1, 8). In plants, numerous PM proteins undergo endocytosis and endosomal recycling, with the PIN-FORMED (PINs) transporters for the plant hormone auxin being the most studied (9). Polarized PM localization of PINs has a profound developmental importance and is tightly regulated by multiple endosomal trafficking routes, including endocytosis, endosomal recycling, and vacuolar degradation. PINs are internalized via clathrin-mediated endocytosis and then recycled back to the PM via the GNOM-positive putative RE … [↵][1]2To whom correspondence should be addressed. Email: ljiang{at}cuhk.edu.hk. [1]: #xref-corresp-1-1