The research group led by Dr. Wan Jianmin at Institute of Crop Sciences (ICS) of CAAS has achieved an important progress on the elucidation of molecular mechanisms regulating the directional trafficking of dense vesicle (DV) to the protein storage vacuole (PSV) in rice endosperm.

The researchers isolated a storage protein sorting deficient mutant from a 60Co-irradiated mutant pool, named glutelin precursor accumulation3 (gpa3). The gpa3 mutant exhibits a floury endosperm phenotype and accumulates high levels of proglutelins in dry seeds. Combination of cytological and immunocytochemistry studies revealed that in the gpa3 mutant, glutelin-filled DVs are missorted to the apoplast, where they forms the abnormal paramural body (PMB) together with some cell wall components (Figure A). Map-based cloning of GPA3 revealed that it encodes a plant-specific kelch-repeat protein. Subcellular localization of GPA3-GFP confirmed that fusion proteins are localized to post-Golgi compartments (e.g. the TGN, DVs, and PSVs). Furthermore, biochemical experiments verified that GPA3 can form a regulatory complex with two previously reported functional factors Rab5a and VPS9a (Figure B). Together, these results indicated that GPA3 can work synergistically with Rab5a and VPS9a to regulate DV-mediated post-Golgi traffic in rice, and provide new insights into the molecular mechanisms regulating the plant-specific PSV pathway in seed plants.

This work was supported by China’s National Natural Science Foundation and the Ministry of Agriculture.

The paper was published online on January 31, 2014 on the international famous journal The Plant Cell.