Instituto de Biologia Molecular y Celular de Plantas, Consejo Superior de Investigaciones Cientificas-Universidad Politecnica de Valencia, ES-46022 Valencia, Spain.
Plant Physiol. 2013 Feb;161(2):931-41. doi: 10.1104/pp.112.208678. Epub 2012 Dec 14.
Abscisic acid (ABA) signaling plays a critical role in regulating root growth and root system architecture. ABA-mediated growth promotion and root tropic response under water stress are key responses for plant survival under limiting water conditions. In this work, we have explored the role of Arabidopsis (Arabidopsis thaliana) PYRABACTIN RESISTANCE1 (PYR1)/PYR1-LIKE (PYL)/REGULATORY COMPONENTS OF ABA RECEPTORS for root ABA signaling. As a result, we discovered that PYL8 plays a nonredundant role for the regulation of root ABA sensitivity. Unexpectedly, given the multigenic nature and partial functional redundancy observed in the PYR/PYL family, the single pyl8 mutant showed reduced sensitivity to ABA-mediated root growth inhibition. This effect was due to the lack of PYL8-mediated inhibition of several clade A phosphatases type 2C (PP2Cs), since PYL8 interacted in vivo with at least five PP2Cs, namely HYPERSENSITIVE TO ABA1 (HAB1), HAB2, ABA-INSENSITIVE1 (ABI1), ABI2, and PP2CA/ABA-HYPERSENSITIVE GERMINATION3 as revealed by tandem affinity purification and mass spectrometry proteomic approaches. We also discovered that PYR/PYL receptors and clade A PP2Cs are crucial for the hydrotropic response that takes place to guide root growth far from regions with low water potential. Thus, an ABA-hypersensitive pp2c quadruple mutant showed enhanced hydrotropism, whereas an ABA-insensitive sextuple pyr/pyl mutant showed reduced hydrotropic response, indicating that ABA-dependent inhibition of PP2Cs by PYR/PYLs is required for the proper perception of a moisture gradient.
脱落酸（ABA）信号转导在调节根生长和根系结构方面起着关键作用。ABA 介导的在水分胁迫下的生长促进和根向性反应是植物在限水条件下生存的关键反应。在这项工作中，我们探索了拟南芥（Arabidopsis thaliana）PYRABACTIN RESISTANCE1（PYR1）/PYR1-LIKE（PYL）/ABA 受体调节因子在根 ABA 信号转导中的作用。结果发现，PYL8 在调节根 ABA 敏感性方面发挥着非冗余的作用。出乎意料的是，考虑到 PYR/PYL 家族的多基因性质和部分功能冗余，单个 pyl8 突变体对 ABA 介导的根生长抑制的敏感性降低。这种效应是由于缺乏 PYL8 介导的对几种 clade A 磷酸酶 2C（PP2C）的抑制，因为 PYL8 在体内与至少五种 PP2C 相互作用，即 HYERSENSITIVE TO ABA1（HAB1）、HAB2、ABA-INSENSITIVE1（ABI1）、ABI2 和 PP2CA/ABA-HYPERSENSITIVE GERMINATION3，这是通过串联亲和纯化和质谱蛋白质组学方法揭示的。我们还发现，PYR/PYL 受体和 clade A PP2C 对于水向性反应至关重要，水向性反应发生以引导根生长远离水势低的区域。因此，ABA 超敏性的 pp2c 四重突变体表现出增强的水向性，而 ABA 不敏感的 sextuple pyr/pyl 突变体表现出降低的水向性反应，表明 PYR/PYL 对 clade A PP2C 的 ABA 依赖性抑制是正确感知水分梯度所必需的。
