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

Abstract

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.

ENDOSOMAL RAB EFFECTOR WITH PX-DOMAIN, an Interacting Partner of RAB5 GTPases, Regulates Membrane Trafficking to Protein Storage Vacuoles in Arabidopsis

“…A subpopulation of canonical RAB5 has been localized to the TGN, which is likely responsible for maturation from the TGN to the multivesicular endosomes (Stierhof and El Kasmi, 2010;Scheuring et al, 2011;Singh et al, 2014). EREX might coordinate cargo sorting and RAB5 activity during this event, which is consistent with the findings that the mutations in AP-4 and sorting nexins that are involved in vacuolar protein transport at the TGN and RAB5-positive endosomes, respectively, exert similar effects on transport of 12S globulin and 2S albumin to the erex erel1 mutation (Pourcher et al, 2010;Fuji et al, 2016).…”

Trafficking of Vacuolar Proteins: The Crucial Role of Arabidopsis Vacuolar Protein Sorting 29 in Recycling Vacuolar Sorting Receptor

“…In addition, these results are consistent with previous studies on the localization of VSRs and sorting nexins. The majority of VSR1 localizes to the PVC with a minor proportion to the TGN (Li et al, 2002;Tse et al, 2004;Kim et al, 2005Kim et al, , 2010, and sorting nexins also localize to the PVC (Jaillais et al, 2006, Pourcher et al, 2010. However, recently, an alternative model for vacuolar cargo sorting by VSRs was proposed by Niemes et al (2010a).…”

“…Consistent with this observation in animal cells, plant cells also appear to contain multiple complexes containing sorting nexin. Triple knockout sorting nexin mutant plants exhibit a defect only in the trafficking of 12S globulin, but vps29 null mutant plants exhibit defects in the trafficking of both 12S globulin and 2S albumin, suggesting that the sorting nexin subcomplex and cargo-selective subcomplex do not always work together (Pourcher et al, 2010).…”

GLUTELIN PRECURSOR ACCUMULATION3Encodes a Regulator of Post-Golgi Vesicular Traffic Essential for Vacuolar Protein Sorting in Rice Endosperm

“…Thus, the DV defines a unique carrier for trafficking of storage proteins to the PSV. Growing evidence is showing that post-Golgi trafficking of storage proteins to the PSV also requires the retromer components (MAG1/VPS29, VPS35, and SNXs) involved in the recycling of VSRs (Shimada et al, 2003(Shimada et al, , 2006Yamazaki et al, 2008;Zouhar et al, 2009;Pourcher et al, 2010), the Rab family of small GTPases as well as their common guanine exchange factor (GEF) for specifying vesicular trafficking (Wang et al, 2010;Ebine et al, 2011;Liu et al, 2013), and the SNARE complex for mediating membrane fusion between post-Golgi compartments (Ebine et al, 2008). However, plantspecific regulators required for these processes largely remain to be identified.…”