Which of the following is an inhibitor of the ethylene biosynthetic pathway
Co2+
Mg2+
Fe2+
Mn2+
ABA receptor and signalling: 1. PYR/RCAR receptors, II. PP2C Protein
Answers
Answer:
Abstract
The phytohormone abscisic acid (ABA), an important bioactive compound in plants, is implicated in several essential processes such as development and the abiotic stress response. Many components have been reported to have roles in these processes. Although 2C-type protein phosphatases (PP2C) and SNF1-related protein kinases2 (SnRK2) family are known to be important signal mediators, the molecular mechanisms by which these components regulate the ABA signaling pathway have not been elucidated. Recent identification of soluble ABA receptors, PYR/PYL/RCAR, has provided a major breakthrough in understanding the signaling mechanisms of ABA and revealed the importance of PP2Cs. In addition, the physical, biochemical and physiological connections between PP2C and SnRK2 have been clearly demonstrated. Taken together, the molecular basis of the major ABA signaling pathway has been established, from perception to gene expression. In this addendum, we discuss this emerging ABA signaling pathway, which has a conventional protein phosphorylation/dephosphorylation regulatory circuit and consider its physiological and functional relevance.
Key words: ABA receptor, abscisic acid, PP2C, signal transduction, SnRK2, plant hormone, phosphoarylation
Introduction
The phytohormone abscisic acid (ABA) has broad physiological functions, not only in the abiotic stress response, but also in developmental processes and the biotic stress response. Its complex physiological activity and huge amount and variety of putative ABA signaling factors suggest that the ABA signaling pathway is a complex network.1,2 However, the emerging picture of the ABA signaling pathway has changed our perception drastically. Recent breakthrough studies have revealed that PYR/PYL/RCAR family proteins function as soluble ABA receptors. These ABA receptors regulate clade A PP2Cs in an ABA-dependent manner. 3,4 We very recently showed that these PP2Cs interact with and inactivate ABA-activated SNF1-related kinase2 (SnRK2) via dephosphorylation and that this PP2C action is inhibited by PYR1 in the presence of ABA.5 These studies have established one of the major ABA signaling pathways consisting of just four factors, PYR/PYL/RCAR ABA receptors—clade A PP2Cs—ABA activated SnRK2s—targets of kinase (e.g., bZIP)(Fig.1). This pathway is as simple as the signaling systems of other plant hormones such as auxin, gibberellin, or jasmonic acid.6 In this addendum, we will review the regulatory steps of the ABA signaling pathway and discuss the relevance of using a phosphorylation/dephosphorylation modification system in the signal transduction pathway of this hormone.