AtRabD2b, a Functional Ortholog of the Yeast Ypt1, Controls Various Growth and Developmental Processes in Arabidopsis

摘要

Rab1-related guanosine-5′-triphosphatases (GTPases) regulate the intracellular endoplasmic reticulum (ER)-to-Golgi vesicle transport in yeast, mammalian and plant systems. Arabidopsis contains four Rab1 GTPases which are further divided into two functionally distinct subclasses, RabD1 and RabD2. In this study, we investigated the function of an Arabidopsis RabD2b gene. Yeast complementary assay demonstrated that AtRabD2b is a functional counterpart of the yeast Ypt1. The active GTP-bound mutant (AtRabD2b [Q67L]) maintained the complementary ability of ypt1 mutant as wild-type AtRabD2b. Both AtRabD2b and AtRabD2b [Q67L] localize on the Golgi stacks and a second subpopulation of punctate structures in tobacco leaf cells. RT-PCR assay showed that AtRabD2b is ubiquitously expressed in different plant tissues. Transgenic plants overexpressing yellow fluorescent protein (YFP)-AtRabD2b [Q67L] fusion gene exhibited dwarfism, altered morphology of rosette leaves, and upward-pointing siliques in the stems. The downregulation of AtRabD1, AtRabD2b, and AtRabD2c, due to cosuppression of the AtRabD2b gene in the YFP-AtRabD2b [Q67L] transgenic plants, resulted in stunted bushy growth phenotype, very low fertility, and the necrosis at the apical region of the stem. Together, these data indicated that AtRabD2b gene regulates the ER-to-Golgi membrane trafficking as Ypt1 and plays a role in several aspects of plant growth and development.