Arabidopsis UNHINGED encodes a VPS51 homolog and reveals a role for the GARP complex in leaf shape and vein patterning

Abstract

Asymmetric localization of PIN proteins controls directionality of auxin transport and many aspects of plant development. Directionality of PIN1 within the marginal epidermis and the presumptive veins of developing leaf primordia is crucial for establishing leaf vein pattern. One mechanism that controls PIN protein distribution within the cell membranes is endocytosis and subsequent transport to the vacuole for degradation. The Arabidopsis mutant unhinged-1 (unh-1) has simpler leaf venation with distal non-meeting of the secondary veins and fewer higher order veins, a narrower leaf with prominent serrations, and reduced root and shoot growth. We identify UNH as the Arabidopsis vacuolar protein sorting 51 (VPS51) homolog, a member of the Arabidopsis Golgi-associated retrograde protein (GARP) complex, and show that UNH interacts with VPS52, another member of the complex and colocalizes with trans Golgi network and pre-vacuolar complex markers. The GARP complex in yeast and metazoans retrieves vacuolar sorting receptors to the transGolgi network and is important in sorting proteins for lysosomal degradation. We show that vacuolar targeting is reduced in unh-1. In the epidermal cells of unh-1 leaf margins, PIN1 expression is expanded. The unh-1 leaf phenotype is partially suppressed by pin1 and cuc2-3 mutations, supporting the idea that the phenotype results from expanded PIN1 expression in the marginal epidermis. Our results suggest that UNH is important for reducing expression of PIN1 within margin cells, possibly by targeting PIN1 to the lytic vacuole.

An Aphid Effector Targets Trafficking Protein VPS52 in a Host-Specific Manner to Promote Virulence

“…Recent evidence suggests that membrane systems, including the Golgi apparatus and the ER, may be present inside sieve elements (Lin et al, 2009;Fröhlich et al, 2012). Also, VPS51, another component of the GARP complex, is expressed in the plant vasculature as well as in the flowers (Pahari et al, 2014). It is therefore possible that aphids may need to manipulate host processes in specific tissues, such as the phloem.…”

“…Although the role of VPS52 in plant cellular trafficking is not well understood, this protein was previously shown to localize to post-Golgi and prevacuolar compartments, suggesting it may have similar functions in trafficking as in other systems (Lobstein et al, 2004;Guermonprez et al, 2008). VPS52 interacts with at least one other component of the GARP-complex in plants, VPS51, which is involved in the maintenance of vacuolar morphology as well as leaf shape and vein patterning (Pahari et al, 2014). A recent proteomics study to identify proteins associated with endosomal and secretory pathways in Arabidopsis revealed the enrichment of VPS52 in pull-downs of RABF1/ARA6, RABG3f, CLC2, RABD2a/ARA5, and RABF2b/ARA7 (Heard et al, 2015).…”

The Plant Trans-Golgi Network: Not Just a Matter of Distinction

“…Mutants of Arabidopsis GARP subunits have implicated the complex in pollen tube elongation, acclimation to heat stress, and vacuolar targeting of the auxin carrier PIN1, necessary for PIN1 polar localization during the establishment of leaf vein patterning (Lobstein et al, 2004;Wang et al, 2011;Pahari et al, 2014). Interestingly, GARP shares three subunits with the Endosome-Associated Recycling Protein (EARP), which resides on recycling endosomes and is required for bringing recycling proteins/cargo to the cell surface (Schindler et al, 2015;Ravikumar et al, 2017).…”

Identification of Regulatory and Cargo Proteins of Endosomal and Secretory Pathways in Arabidopsis thaliana by Proteomic Dissection*

“…The A. thaliana COG2 (AT4G24840) subunit has recently been shown to recruit the exocyst subunit EXO70A1 to punctate structures at cortical microtubules during xylem formation (94). The putative COG1 subunit (AT5G16300) has also been annotated as a possible GARP complex subunit (VPS51) (95). We have placed AT5G16300 in the COG group of Table III, but it could equally belong to the GARP complex.…”