Ypt1 suppresses defects of vesicle trafficking and autophagy in Ypt6 related mutants

Ypt/Rab GTPases coordinately regulate vesicle trafficking in yeasts. Previously, Ypt1 was shown to suppress growth defects of Ypt6 and its related mutants (ypt6ts, ric1∆, rgp1∆, ric1∆rgp1∆), but the physiological role of this suppression has not been well studied. We have investigated the effects of Ypt1 on two major trafficking pathways, vesicle trafficking and autophagy, in Ypt6 related mutants. Ypt1 restores Snc1 transport to the plasma membrane via Golgi in the exocytic pathway in Ypt6 related mutants under nutrient rich conditions. Overexpression of Ypt1 suppresses autophagic defects under nutrient starvation conditions with increased GFP-Atg8 sorting to vacuoles and GFP-Atg8 to GFP conversion in Ypt6 related mutants. However, overexpression of Ypt1 does not restore Ypt6 intracellular localisation in rgp1∆ cells. We propose that vesicle trafficking and autophagy are closely connected processes, and Ypt1 and Ypt6 have some similar functions in both cellular processes.