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

Abstract

Dense vesicles (DVs) are vesicular carriers, unique to plants, that mediate post-Golgi trafficking of storage proteins to protein storage vacuoles (PSVs) in seeds. However, the molecular mechanisms regulating the directional targeting of DVs to PSVs remain elusive. Here, we show that the rice (Oryza sativa) glutelin precursor accumulation5 (gpa5) mutant is defective in directional targeting of DVs to PSVs, resulting in discharge of its cargo proteins into the extracellular space. Molecular cloning revealed that GPA5 encodes a plant-unique phox-homology domain-containing protein homologous to Arabidopsis (Arabidopsis thaliana) ENDOSOMAL RAB EFFECTOR WITH PX-DOMAIN. We show that GPA5 is a membrane-associated protein capable of forming homodimers and that it is specifically localized to DVs in developing endosperm. Colocalization, biochemical, and genetic evidence demonstrates that GPA5 acts in concert with Rab5a and VPS9a to regulate DV-mediated post-Golgi trafficking to PSVs. Furthermore, we demonstrated that GPA5 physically interacts with a class C core vacuole/ endosome tethering complex and a seed plant-specific VAMP727-containing R-soluble N-ethylmaleimide sensitive factor attachment protein receptor complex. Collectively, our results suggest that GPA5 functions as a plant-specific effector of Rab5a required for mediating tethering and membrane fusion of DVs with PSVs in rice endosperm.

Effects of High Temperature on Rice Grain Development and Quality Formation Based on Proteomics Comparative Analysis Under Field Warming

“…Grain storage protein precursors such as glutelin precursors are synthesized in the endoplasmic reticulum, and then folded and modified with the help of a series of molecular chaperones to form trimers. These trimers are then transported out of the endoplasmic reticulum through vesicles, and eventually transported to protein storage vacuoles to form protein bodies (PB II) (Ren et al, 2020 ). During this process, the molecular chaperone heat shock protein family such as Hsp70/BiP located at the endoplasmic reticulum can promote the correct folding of glutelin and keeps the protein stable during the folding and assembly process.…”

Correlations Between Parental Lines and Indica Hybrid Rice in Terms of Eating Quality Traits

“…So far, numerous studies have examined the physicochemical properties and molecular structure of starch in conventional rice (15)(16)(17)(18)(19)(20)(21). However, relatively little research has investigated hybrid rice (22)(23)(24).…”

Rice seed storage proteins: Biosynthetic pathways and the effects of environmental factors

“…Mutants in which proglutelin cannot be cleaved in PSVs due to a defect in the membrane trafficking system are collectively referred to as 57H mutants, which include glup and gpa mutants. The rice mutants gpa1/glup4/rab5a (Wang et al, 2010;Fukuda et al, 2011), gpa2/glup6/vps9a (Fukuda et al, 2013;Liu et al, 2013), gpa3 (Ren et al, 2014), and gpa5 (Ren et al, 2020) exhibit defective DV-mediated post-Golgi trafficking because some DVs containing proglutelins and α-globulins are mistargeted to the plasma membrane to form PMBs.…”

“…GPA3 functions as an adaptor protein to recruit VPS9a to activate Rab5a and facilitates the maturation of proglutelin/αglobulin-containing DVs from the TGN (Ren et al, 2014). Activated Rab5a recruits its effector GPA5, and GPA5 then interacts with the class C core vacuole/endosome tethering (CORVET) complex and a seed plant-specific VESICLE AS-SOCIATED MEMBRANE PROTEIN727 (VAMP727)-containing R-soluble NSF attachment protein receptor (SNARE) complex to perform DV-to-PSV fusion (Figure 1E) (Ren et al, 2020). Notably, the loss of GPA5 function leads to only a moderate sorting defect among proglutelins, suggesting that another pathway also contributes to the trafficking of proglutelins to the PSVs in rice endosperm.…”