Analyses of SORTING NEXINs Reveal Distinct Retromer-Subcomplex Functions in Development and Protein Sorting in Arabidopsis thaliana

Sorting nexins (SNXs) are conserved eukaryotic proteins that associate with three types of vacuolar protein sorting (VPS) proteins to form the retromer complex. How SNXs act in this complex and whether they might work independently of the retromer remains elusive. Here, we show by genetic and cell imaging approaches that the Arabidopsis thaliana SNX1 protein recruits SNX2 at the endosomal membrane, a process required for SNX1-SNX2 dimer activity. We report that, in contrast with the mammalian retromer, SNXs are dispensable for membrane binding and function of the retromer complex. We also show that VPS retromer components can work with or independently of SNXs in the trafficking of seed storage proteins, which reveals distinct functions for subcomplexes of the plant retromer. Finally, we provide compelling evidence that the combined loss of function of SNXs and VPS29 leads to embryo or seedling lethality, underlining the essential role of these proteins in development.