Vesicle formation and recycling in the secretory pathway - from yeast to higher plants

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Studies on yeast :1) We analyzed ts alleles of Arf1 GTPase and isolated multicopy suppressors. We suggested that different GEFs and GAPs are involved in an allele-specific manner. 2) We demonstrated that Rer1p is a sorting receptor in the Golgi that retrieves a subset of ER membrane proteins. We also identified the Golgi-localization signals of Rer1p and showed that they interact with COPI components. 3) We identified ER-localization signals of Sec12p and Sec71p. We also crystalized Sec12p and analyzed its 3-D structure. 4) We showed that ergosterol is essential for targeting of the tryptophan permease Tat2p to the plasma membrane. 5) We demonstrated that both Rer2p and its homologue Srt1p have the cis-prenyltransferase activity but show different characteristics.Studies on plants :1) We introduced dominant negative mutants of AtARF1 into plant cells and showed that its expression inhibits ER-Golgi traffic. 2) We identified Ara6 and Ara7 as new members of the Rab GTPase family and showed that they function in endosomes. We showed that Ara6 has uniques features distinct from other conventional Rab GTPases. 3) We showed that Arabidopsis RMA1, originally isolated as a suppressor of the yeast sec15 mutant, encodes a novel membrane-bound ubiquitin ligase. 4) We showed that vacuole membranes of Arabidopsis plants as visualized by γTIP-GFP display very dynamic and complex structures. 5) We demonstrated from the analysis of Arabidopsis shoot gravitropism mutants that vacuole biogenesis plays very important roles in the sensing of the gravity.