Abstract
Sphingolipid metabolites, sphingoid long-chain base (LCB) 1-phosphates (LCB-1Ps), are involved in ABA signaling pathways. The LCB-1Ps synthesized by LCB kinase are dephosphorylated by LCB-1P phosphatase or degraded by LCB-1P lyase. In the present study, we show that the At3g58490 gene encodes AtSPP1, a functional LCB-1P phosphatase involved in ABA-mediated stomatal responses. Transient expression of green fluorescent protein fusion in suspension-cultured Arabidopsis cells showed that AtSPP1 localizes on the endoplasmic reticulum. We isolated and characterized Arabidopsis spp1 mutants, in which the AtSPP1 gene is knocked out by T-DNA insertion. After drought stress, the rate of decrease in fresh weight was significantly slower in spp1 mutants than in the wild-type plants. A stomatal aperture bioassay showed that stomatal closure occurs in responses to ABA in spp1 mutants, suggesting that AtSPP1 is involved in guard-cell signaling. spp1 mutants also showed decreased sensitivity to ABA with respect to primary root growth but not to seed germination. The response to fumonisin B1 did not differ between wild-type and spp1 mutant.
