Post-Golgi trafficking of rice storage proteins requires the small GTPase Rab7 activation complex MON1–CCZ1

• DOI: 10.1093/plphys/kiab175
• Publication Date: 2021-04-16T19:14:39Z
• Authors: Tian Pan; Yihua Wang; Ruonan Jing; Yongfei Wang; Zhongyan Wei; Binglei Zhang; Cailin Lei; Yanzhou Qi; Fan Wang; Xiuhao Bao; Mengyuan Yan; Yu Zhang; Pengcheng Zhang; Mingzhou Yu; Gexing Wan; Yu Chen; Wenkun Yang; Jianping Zhu; Yun Zhu; Shanshan Zhu; Zhijun Cheng; Xin Zhang; Ling Jiang; Yulong Ren; Jianmin Wan
• Keywords: Crops, Agricultural; 0301 basic medicine; 2. Zero hunger; China; Genotype; Glutens; Vesicular Transport Proteins; Genetic Variation; Oryza; Genes, Plant; 03 medical and health sciences; Gene Expression Regulation, Plant; rab GTP-Binding Proteins; Mutation; Seeds

Abstract Protein storage vacuoles (PSVs) are unique organelles that accumulate storage proteins in plant seeds. Although morphological evidence points to the existence of multiple PSV-trafficking pathways for storage protein targeting, the molecular mechanisms that regulate these processes remain mostly unknown. Here, we report the functional characterization of the rice (Oryza sativa) glutelin precursor accumulation7 (gpa7) mutant, which over-accumulates 57-kDa glutelin precursors in dry seeds. Cytological and immunocytochemistry studies revealed that the gpa7 mutant exhibits abnormal accumulation of storage prevacuolar compartment-like structures, accompanied by the partial mistargeting of glutelins to the extracellular space. The gpa7 mutant was altered in the CCZ1 locus, which encodes the rice homolog of Arabidopsis (Arabidopsis thaliana) CALCIUM CAFFEINE ZINC SENSITIVITY1a (CCZ1a) and CCZ1b. Biochemical evidence showed that rice CCZ1 interacts with MONENSIN SENSITIVITY1 (MON1) and that these proteins function together as the Rat brain 5 (Rab5) effector and the Rab7 guanine nucleotide exchange factor (GEF). Notably, loss of CCZ1 function promoted the endosomal localization of vacuolar protein sorting-associated protein 9 (VPS9), which is the GEF for Rab5 in plants. Together, our results indicate that the MON1–CCZ1 complex is involved in post-Golgi trafficking of rice storage protein through a Rab5- and Rab7-dependent pathway.