A putative endosomal t-SNARE links exo- and endocytosis in the phytopathogenic fungus Ustilago maydis

We identified a temperature-sensitive mutant of the plant pathogenic fungus Ustilago maydis that is defective in the polar distribution of cell wall c omponents and shows abnormal morphology. The affected gene, yup1, was clone d by complementation. It encodes a putative target soluble N-ethylmaleimide -sensitive fusion protein attachment protein receptor (t-SNARE), suggesting a function in membrane fusion, A Yup1-GFP fusion protein localized to vesi cles that showed rapid saltatory motion along microtubules, These vesicles are part of the endocytic pathway and accumulate at sites of active growth, thereby supporting the expansion of the hyphal tip. In yup1(ts) cells, end ocytosis is impaired and accumulation of Yup1-carrying endosomes at cell po les is abolished, resulting in apolar distribution of wall components and m orphological alterations. This suggests that a membrane recycling process v ia early endosomes supports polar growth of U.maydis.