CS-12-1 - - Vacuole fusion mechanisms mediated by SNAREs and HOPS
Monday, July 16
1:03 PM - 1:23 PM
The vacuole is an essential organelle in plant cells, and its dynamics is important for plant growth and development. Homotypic membrane fusion is required for vacuole biogenesis, pollen germination, stomata opening and gravity perception. Known components of the vacuole fusion machinery in eukaryotes include SNARE proteins, Rab GTPases, phosphoinositides and the homotypic fusion and vacuolar protein sorting (HOPS) tethering complex. HOPS function is not well characterized in plants, but roles in embryogenesis and pollen tube elongation have been reported. We determined that two HOPS subunits of Arabidopsis, VPS33 and VPS41, are soluble proteins that can associate with endomembrane compartments, but only VPS41 is found in the tonoplast. Inducible knockdown of VPS41 resulted in dramatic vacuole fragmentation phenotypes and demonstrated a critical role for HOPS in homotypic vacuole fusion.We used genetic and biochemical approaches to test interactions between HOPS and SNARE subunits that regulate vacuole fusion, and found that a functional SNARE complex is required for normal VPS41 localization. Our results suggest that VPS33 and SYP22 define the initial stage for HOPS-SNARE interactions, and highlight conserved mechanisms for HOPS function in regulating SNAREs during vacuole fusion.