Phosphatidylinositol 4,5‐bisphosphate is important for stomatal opening

Previously, we demonstrated that a protein that binds phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P 2 ] inhibits both light-induced stomatal opening and ABA-induced stomatal closing. The latter effect is due to a reduction in free PtdIns(4,5)P 2 , decreasing production of inositol 1,4,5-trisphosphate and phosphatidic acid by phospholipases C and D. However, it is less clear how PtdIns(4,5)P 2 modulates stomatal opening. We found that in response to white light irradiation, the PtdIns(4,5)P 2 -binding domain GFP:PLC61PH translocated from the cytosol into the plasma membrane. This suggests that the level of PtdIns(4,5)P 2 increases at the plasma membrane upon illumination. Exogenously administered PtdIns(4,5)P 2 substituted for light stimuli, inducing stomatal opening and swelling of guard cell protoplasts. To identify PtdIns(4,5)P 2 targets we performed patch-clamp experiments, and found that anion channel activity was inhibited by PtdIns(4,5)P 2 . Genetic analyses using an Arabidopsis PIP5K4 mutant further supported the role of PtdIns(4,5)P 2 in stomatal opening. The reduced stomatal opening movements exhibited by a mutant of Arabidopsis PIP5K4 (At3g56960) was countered by exogenous application of PtdIns(4,5)P 2 . The phenotype of reduced stomatal opening in the pip5k4 mutant was recovered in lines complemented with the full-length PIP5K4. Together, these data suggest that PIP5K4 produces PtdIns(4,5)P 2 in irradiated guard cells, inhibiting anion channels to allow full stomatal opening.