Arabidopsis EXO70A1 recruits Patellin3 to the cell membrane independent of its role as an exocyst subunit

The exocyst is a well-known complex which tethers vesicles at the cell membrane before fusion. Whether an individual subunit can execute a unique function is largely unknown. Using yeast-two-hybrid （Y2H） analysis, we found that EXO7oA1 interacted with the GOLD domain of Patellin3 （PATL3）. The direct EXO7OA1-PATL3 interaction was supported by in vitro and in vivo experiments. In Arabidopsis, PATL3-GFP colocalized with EXO7oA1 predominantly at the cell membrane, and PATL3 localization was insensitive to BFA and TryA23. Remarkably, in the exo7oa1 mutant, PATL3 proteins accumulated as punctate structures within the cytosol, which did not colocalize with several endomembrane compartment markers, and was insensitive to BFA. Furthermore, PATL3 localization was not changed in the exo7oe2, PRsec6 or exo84b mutants. These data suggested that EXO7oA1, but not other exocyst subunits, was responsible for PATL3 localization, which is independent of its role in secretory/recycling vesicletethering/fusion. Both EXO7oA1 and PATL3 were shown to bind PI4P and PI（4,5）P2 in vitro. Evidence was obtained that the other four members of the PATL family bound to EXO7oA1 as well, and shared a similar localization pattern as PATL3. These findings offered new insights into exocyst subunitspecific function, and provided data and tools for further characterization of PATL family proteins.