Data from: Regulation of vacuole fusion in stomata by dephosphorylation of the HOPS subunit VPS39

Understanding how plants regulate water loss is important for improving
crop productivity. Tight control of stomatal opening and closing is
essential for the uptake of CO2 while mitigating water vapor loss. The
opening of stomata is regulated in part by homotypic vacuole fusion, which
is mediated by conserved homotypic vacuole protein sorting (HOPS) and
vacuolar SNARE (soluble N-ethylmaleimide sensitive factor attachment
protein receptors) complexes. HOPS tethers apposing vacuole membranes and
promotes the formation of trans-SNARE complexes to mediate fusion. In
yeast, HOPS dissociates from the assembled SNARE complex to complete
vacuole fusion, but little is known about this process in plants.
HOPS-specific subunits VACUOLE PROTEIN SORTING39 (VPS39) and VPS41 are
required for homotypic plant vacuole fusion, and a computational model
predicted that post-translational modifications of HOPS may be needed for
plant stomatal vacuole fusion. Here, we characterized a viable T-DNA
insertion allele of VPS39 which demonstrated a critical role of VPS39 in
stomatal vacuole fusion. We found that VPS39 has increased levels of
phosphorylation at S413 when stomata are closed versus open, and that
VPS39 function in stomata and embryonic development requires dynamic
changes in phosphorylation. Among all HOPS and vacuolar SNARE subunits,
only VPS39 showed differential levels of phosphorylation between open and
closed stomata. Moreover, regions containing S413 are not conserved
between plants and other organisms, suggesting plant-specific mechanisms.
 Our data are consistent with VPS39 phosphorylation altering
vacuole dynamics in response to environmental cues, similar to
well-established phosphorylation cascades that regulate ion transport
during stomatal opening.