An Arabidopsis Inositol 5-Phosphatase Gain-of-Function Alters Abscisic Acid Signaling

Abstract

Signals can be perceived and amplified at the cell membrane by receptors coupled to the production of a variety of second messengers, including inositol 1,4,5-trisphosphate (IP₃). We previously have identified 15 putative inositol 5-phosphatases (5PTases) from Arabidopsis and shown that At5PTase1 can hydrolyze IP₃. To determine whether At5PTase1 can terminate IP₃-mediated signaling, we analyzed transgenic plants ectopically expressing At5PTase1. Stomata from leaves of At5PTase1 transgenic plants were abscisic acid (ABA) and light insensitive, and ABA induction of genes was delayed. Quantification of IP₃ in plants exposed to ABA indicated that ABA induced two IP₃ increases in wild-type plants. Both of these IP₃ increases were reduced in At5PTase1 transgenic plants, indicating that IP₃ may be necessary for stomatal closure and temporal control of ABA-induced gene expression. To determine if ABA could induce expression of At5PTase1, we examined RNA and protein levels of At5PTase1 in wild-type plants exposed to ABA. Our results indicate that At5PTase1 is up-regulated in response to ABA. This is consistent with At5PTase1 acting as a signal terminator of ABA signaling.