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

Abstract

ORCID ID: 0000-0001-7441-0203 (H.T.S.)RAB5 GTPases act as molecular switches that regulate various endosomal functions in animal cells, including homotypic fusion of early endosomes, endosomal motility, endosomal signaling, and subcompartmentalization of the endosomal membrane. RAB5 proteins fulfill these diverse functions through interactions with downstream effector molecules. Two canonical RAB5 members, ARA7 and RAB HOMOLOG1 (RHA1), are encoded in the Arabidopsis thaliana genome. ARA7 and RHA1 play crucial roles in endocytic and vacuolar trafficking pathways. Plant RAB5 GTPases function via interactions with effector molecules, whose identities and functions are currently unclear. In this study, we searched for canonical RAB5 effector molecules of Arabidopsis and identified a candidate, which we called ENDOSOMAL RAB EFFECTOR WITH PX-DOMAIN (EREX). The intimate genetic interaction between EREX and RAB5 members, the results from subcellular colocalization experiments, and the direct interaction observed in an in vitro pull-down assay strongly suggest that EREX is a genuine effector of canonical RAB5s in Arabidopsis. We further found that close homologs of EREX play partially redundant functions with EREX in the transport of seed storage proteins. Our results indicate that canonical plant RAB5s acquired distinct effector molecules from those of non-plant systems to fulfill their functions.

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“…Specifically, PX domain-containing protein EREX is engaged in vacuolar transport of storage proteins. It controls membrane trafficking to protein storage vacuoles (PSVs) and attaches explicitly to phosphatidylinositol 3-monophosphate[18].Protein Light-Dependent Short Hypocotyls 1 is a plausible transcription regulator that performs as a developmental regulator by stimulating cell growth in reaction to continuous red, far-red and blue light in a phytochrome-dependent mode[19]. BTB/POZ domain-containing protein NPY1 operates as a substrate-specific adapter of an E3 ubiquitin-protein ligase complex (CUL3-RBX1-BTB) which facilitates the ubiquitination and consequent proteasomal degradation of target proteins.…”

GPA5 Encodes a Rab5a Effector Required for Post-Golgi Trafficking of Rice Storage Proteins

“…Cytological evidence demonstrates that the mutation in GPA5 causes fusion of DVs with the plasma membrane, thereby discharging their contents into the apoplast space. GPA5 encodes a plant-unique phox-homology (PX) domain-containing protein homologous to the previously reported Arabidopsis (Arabidopsis thaliana) EREX, EREX-LIKE1 (EREL1), and EREL2 proteins (Sakurai et al, 2016). We show that GPA5 is a peripheral membrane protein and that it is specifically localized to mature DVs in developing endosperm.…”

Evolutionary insights into PtdIns3P signaling through FYVE and PHOX effector proteins from the moss Physcomitrella patens

“…AtSNX1 function as a sorting endosome from which endocytosed plasma membrane (PM) proteins, such as the Iron-Regulated Transporter1 (IRT1) or the auxin efflux carrier PIN2 and secretory proteins are sorted to diverse destinations (Ivanov et al 2014, Jaillais et al 2008, Jaillais et al 2006, Pourcher et al 2010). In addition, AtSNX2a and AtSNX2b, have distinct functions in trafficking of storage proteins and plant development (Pourcher et al 2010), whereas AtEREX, another PHOX-domain protein, was recently suggested as a genuine effector of canonical RAB5s in A. thaliana (Sakurai et al 2016).…”

“…The class II is represented by PpPX1 and PpPX2, and exhibit only a PHOX domain positioned close to the N-terminus. A. Endosomal Rab Effector with PX-domain) protein has been suggested as a genuine effector of canonical RAB5s mediating vacuolar trafficking(Sakurai et al 2016). Members of class III are single proteins in all species analyzed with exception of G. max, and are represented by PpSXN5 in P. patens.These proteins exhibit a PHOX and a C-terminal RING9 domain, but none physiological role has been assigned to this group yet.…”