Institute of Plant Science, Volcani Center, ARO, Bet-Dagan, Israel.
Plant Cell Rep. 2012 Feb;31(2):311-21. doi: 10.1007/s00299-011-1166-z. Epub 2011 Oct 21.
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.
非生物胁迫耐受的分子调控机制基于特定胁迫相关基因的激活和调控。植物激素脱落酸（ABA）是植物应对这些胁迫的关键内源性信使。最近发现了一种新型的 ABA 结合机制，该机制在植物细胞信号级联中发挥关键作用。在没有 ABA 的情况下，一种类型 2C 蛋白磷酸酶（PP2C）相互作用并抑制激酶 SnRK2。ABA 与 PYR/PYL 受体结合使 ABA 受体与 PP2C 蛋白相互作用，并使 SnRK2 失活。然后，活性 SnRK2 可以自由激活靶向 ABA 依赖基因表达的 ABA 响应元件结合因子。我们使用葡萄作为模型来研究果树中的 ABA 感知机制。葡萄 ABA 信号级联至少包含七个 ABA 受体和六个 PP2C。我们使用酵母双杂交系统体外研究了葡萄 ABA 受体与其相互作用伙伴之间的物理相互作用，发现有二十二个受体-PP2C 相互作用可能发生。此外，通过使用 LacZ 报告基因对这些亲和力进行定量，我们可以证明 VvPP2C4 和 VvPP2C9 是 ABA 受体的主要结合伙伴。我们还在存在外源 ABA 以及不同非生物胁迫（如高盐浓度、寒冷和干旱）下，在根和叶中测试了各种 ABA 受体和 PP2C 的基因表达，发现这些基因中的许多都受到这些非生物环境因素的调控。我们的结果表明 ABA 受体基因在器官中具有特异性，而 VvPP2C 在胁迫中具有特异性。我们认为 VvPP2C4 是叶片和根部 ABA 感知中主要的 PP2C，而 VvRCAR6 和 VvRCAR5 分别是这些器官中 ABA 感知的主要受体。鉴定、表征和操纵果树中 ABA 信号级联的核心因子，对于提高其未来的性能可能至关重要。
