Dynamics and Environmental Responses of PATROL1 in Arabidopsis Subsidiary Cells

The Arabidopsis stomatal complex is composed of a pair of guard cells and surrounding anisocytic subsidiary cells. Subsidiary cells are thought to function as a supplier and receiver of bulk water and ions, and to assist turgor-driven stomatal movement, but the molecular mechanisms are largely unknown. In this work, we studied the dynamic behavior and environmental responses of PATROL1, which has been identified as a translocation factor of the plasma membrane proton pump ATPase (PM H+-ATPase) AHA1 in guard cells and subsidiary cells in Arabidopsis thaliana. Variable-angle epifluorescence microscopic observation revealed that green fluorescent protein (GFP)-PATROL1 localized on dot-like compartments that resided on plasma membranes for several seconds. The GFP-PATROL1-labeled dots were sensitive to phosphatidylinositol 4-kinase inhibitors but not to a phosphatidylinositol 3-kinase inhibitor. GFP-PATROL1 and red fluorescent protein (RFP)-AHA1 co-localized in hyperosmotic conditions, and a mutation of PATROL1 resulted in an increase in GFP-AHA1 internalization, suggesting a role in the translocation of PM H+-ATPase in subsidiary cells. Interestingly, subsidiary cells showed changes in localization of GFP-PATROL1 in response to environmental stimuli that were opposite to those in guard cells. Our observations suggested that PATROL1 may contribute to stomatal movement by translocations of PM H+-ATPase in subsidiary cells.