Inactivation of AtRac1 by abscisic acid is essential for stomatal closure

Abstract

Plant water homeostasis is maintained by the phytohormone abscisic acid (ABA), which triggers stomatal pore closure in response to drought stress. We identified the Arabidopsis small guanosine triphosphatase (GTPase) protein AtRac1 as a central component in the ABA-mediated stomatal closure process. ABA treatment induced inactivation of AtRac GTPases and disruption of the guard cell actin cytoskeleton. In contrast, in the ABA-insensitive mutant abi1-1, which is impaired in stomatal closure, neither AtRac inactivation nor actin cytoskeleton disruption was observed on ABA treatment. These observations indicate that AtRac1 inactivation is a limiting step in the ABA-signaling cascade leading to stomatal closure. Consistent with these findings, expression of a dominant-positive mutant of AtRac1 blocked the ABA-mediated effects on actin cytoskeleton and stomatal closure in wild-type plants, whereas expression of a dominant-negative AtRac1 mutant recapitulated the ABA effects in the absence of the hormone. Moreover, the dominant-negative form of AtRac1 could also restore stomatal closure in abi1-1. These results define AtRac1 as a central element for plant adaptation to drought.

Protein Geranylgeranyltransferase I Is Involved in Specific Aspects of Abscisic Acid and Auxin Signaling in Arabidopsis

“…The enhanced ABA response of ggb guard cells is consistent with the observation that Rop6 is a negative regulator of ABA signaling in guard cells (Lemichez et al, 2001). This small GTP-binding protein has a consensus CSIL motif at its C terminus with an upstream polybasic domain, which qualifies it as a putative substrate of PGGT I. Rop2, which possesses a C-terminal CAFL motif and can be geranylgeranylated in vitro (D.N.…”

“…org/ptmdb/results.htm). These include eight Rop GTPases, which regulate actin organization (Fu et al, 2001(Fu et al, , 2002Gu et al, 2003), pollen tube tip growth (Lin et al, 1996;Fu et al, 2001;Gu et al, 2003), ABA and auxin signaling (Lemichez et al, 2001;Li et al, 2001;Tao et al, 2002), and other processes; AIG1, which is involved in RPS2-and avrRpt2-dependent responses to Pseudomonas infection (Reuber and Ausubel, 1996); Aux2-11, a negative regulator of auxin signaling (Wyatt et al, 1993;Caldelari et al, 2001;Dharmasiri and Estelle, 2002); and other proteins. Thus, it is surprising that era1, ggb, and plp phenotypes are not more severe.…”

Diurnal and seasonal variation in root xylem embolism in neotropical savanna woody species: impact on stomatal control of plant water status

“…It is then logical to infer that the magnitude of daily refilling of root xylem forms part of this hydraulic signal between roots and shoots. Our results do not preclude the interaction of hydraulic and chemical signals such as abscisic acid (Gowing, Davies & Jones 1990;Lemichez et al 2001) in governing stomatal response to variation in root embolism. The strong relationship between native k s and the daily fluctuation in Y root (Fig.…”

OSM1/SYP61: A Syntaxin Protein in Arabidopsis Controls Abscisic Acid–Mediated and Non-Abscisic Acid–Mediated Responses to Abiotic Stress

“…Through mutational analysis of Arabidopsi s , a number of other loci have been identified that control stomatal and other responses to ABA (e.g., ERA1 , ERA2 , ERA3 , FUS3 , LEC1 , GCA , and GPA ) (Leung and Giraudat, 1998;Schroeder et al, 2001). Most recently, unexpected loci that encode proteins involved in RNA metabolism (Hugouvieux et al, 2001;Xiong et al, 2001a) and a RHO-like GTPase (Hugouvieux et al, 2001;Lemichez et al, 2001) that controls guard cell cytoskeleton responses to ABA also have been found to mediate stomatal function. In addition, genetic loci in other species have been found to affect ABA-mediated responses, including those of stomata (Leung and Giraudat, 1998).…”