Characterization of potential ABA receptors in Vitis vinifera

Abstract

Molecular control mechanisms for abiotic stress tolerance are based on the activation and regulation of specific stress-related genes. The phytohormone abscisic acid (ABA) is a key endogenous messenger in a plant's response to such stresses. A novel ABA binding mechanism which plays a key role in plant cell signaling cascades has recently been uncovered. In the absence of ABA, a type 2C protein phosphatase (PP2C) interacts and inhibits the kinase SnRK2. Binding of ABA to the PYR/PYLs receptors enables interaction between the ABA receptor and the PP2C protein, and abrogates the SnRK2 inactivation. The active SnRK2 is then free to activate the ABA-responsive element Binding Factors which target ABA-dependent gene expression. We used the grape as a model to study the ABA perception mechanism in fruit trees. The grape ABA signaling cascade consists of at least seven ABA receptors and six PP2Cs. We used a yeast two-hybrid system to examine physical interaction in vitro between the grape ABA receptors and their interacting partners, and found that twenty-two receptor-PP2C interactions can occur. Moreover, quantifying these affinities by the use of the LacZ reporter enables us to show that VvPP2C4 and VvPP2C9 are the major binding partners of the ABA receptor. We also tested in vivo the root and leaf gene expression of the various ABA receptors and PP2Cs in the presence of exogenic ABA and under different abiotic stresses such as high salt concentration, cold and drought, and found that many of these genes are regulated by such abiotic environmental factors. Our results indicate organ specificity in the ABA receptor genes and stress specificity in the VvPP2Cs. We suggest that VvPP2C4 is the major PP2C involved in ABA perception in leaves and roots, and VvRCAR6 and VvRCAR5 respectively, are the major receptors involved in ABA perception in these organs. Identification, characterization and manipulation of the central players in the ABA signaling cascades in fruit trees is likely to prove essential for improving their performance in the future.

ABA-deficiency and molecular mechanisms involved in the dehydration response and ripening of citrus fruit

“…It appeared that these proteins were less represented in Citrus than in Arabidopsis (Park et al, 2009;Ma et al, 2009) and Vitis (Boneh et al, 2012a;Boneh et al, 2012b).…”

“…The elucidation of the ABA signalling core components and the molecular mechanisms by which ABA signal is transduced downstream in the pathway have encouraged new investigations addressed to understand the regulation of ABArelated processes in crops of agronomic interest Sun et al, 2011;Li et al, 2012;Kim et al, 2012;Boneh et al, 2012a;Boneh et al, 2012b).…”

“…Sun et al (2011) performed a transcriptional study in which the relationship between ABA and the PP2CAs gene-regulation was highlighted in different organs, developmental stages and in response to water stress. Studies performed in grape identified six putative PP2CAs and revealed that their expressions in leaves and roots were highly regulated by abiotic ABAincreasing stresses such as high salt concentration, cold and drought (Boneh et al, 2012a;Boneh et al, 2012b), and that sugar and exogenous ABA regulated these and other ABA-signalling genes during ripening of this non-climacteric fruit (Gambetta et al, 2011). Therefore, recent works in crops of agronomic value attempt to find potential targets for biotechnological research.…”

“…Recent works on the ABA-response signalling mechanisms have been particularly relevant to agriculture since they provide a deeper insight into the molecular events involved in stress tolerance. Thus, the discovery of the pyrabactin-resistant (PYR/PYL/RCAR) soluble ABA receptors (Ma et al, 2009;Park et al, 2009;Santiago et al, 2009;Nishimura et al, 2010) (Li et al, 2009;Chai et al, 2011;Sun et al, 2011;Boneh et al, 2012a;Boneh et al, 2012b;Kim et al, 2012;Li et al, 2012;). In citrus,…”

“…In grape, three PYR/PYL/RCAR genes have been isolated (Li et al, 2012a), although only one of them showed the ability to bind ABA and to inhibit the phosphatase activity of ABI1. Further studies revealed that grape ABA signalling cascade consists of at least seven ABA receptors showing organ and stress specificity (Boneh et al, 2012b).…”