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Phosphatidylinositol (PI) metabolism plays a central role in signaling pathways in both animals and higher plants. Stomata) guard cells have been reported to contain PI 3-phosphate (131313) and PI 4-phosphate (PI3P) and PI 4-phosphate (PI4P), the products of PI 3-kinase (PI3K) and PI 4-kinase (PI4K) activities. In this study, we tested the roles of PI3P and P14P in stomatal movements. Both wortmannin (WM) and LY294002 inhibited P13K and P14K activities in guard cells and promoted stomatal opening induced by white light or the circadian clock. WM and LY294002 also inhibited stomatal closing induced by abscisic acid (ABA). Furthermore, overexpression in guard cells of GFP:EBD (green fluorescent protein:endosome binding domain of human EEA1) or GFP:FAPP1 PH (PI-four-P adaptor protein-1 pleckstrin homology domain), which bind to PI3P and PI4P, respectively, increased stomatal apertures under darkness and white light and partially inhibited stomata) closing induced by ABA. The reduction in ABA-induced stomatal closing with reduced levels of PI monophosphate seemed to be attributable, at least in part, to impaired Ca2+ signaling, because WM and LY294002 inhibited ABA-- induced cytosolic Ca2+ increases in guard cells. These results suggest that PI3P and PI4P play an important role in the modulation of stomatal closing and that reductions in the levels of functional PI3P and PI4P enhance stomatal opening.
INTRODUCTION
ACKNOWLEDGMENTS
We thank S.D. Emr for yeast strains and B. Drobak and S. Lee for providing protocols for the PI kinase assay. We also thank Myungki Min for performing the fat-protein gel blot experiment. This research was supported by the Crop Functional Genomics Center of Korea (Grant CG1-1-15) and the Pohang University of Science and Technology Basic Science Research Institute research fund awarded to Y.L. and in part by National Science Foundation Grant MCB 0077791 (to J.LS.). J.M.K. was supported by a fellowship from the Human Frontier Science Program Organization. This work also was supported in part by a grant from the National Creative Research Initiatives program of the Ministry of Science and Technology (Korea) to LH.
Received April 24, 2002; accepted July 1, 2002.
REFERENCES
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