Saez Angela, Robert Nadia, Maktabi Mohammad H, Schroeder Julian I, Serrano Ramón, Rodriguez Pedro L
Instituto de Biología Molecular y Celular de Plantas, Universidad Politécnica de Valencia-Consejo Superior de Investigaciones Científicas, E-46022 Valencia, Spain.
Plant Physiol. 2006 Aug;141(4):1389-99. doi: 10.1104/pp.106.081018. Epub 2006 Jun 23.
Abscisic acid (ABA) plays a key role in plant responses to abiotic stress, particularly drought stress. A wide number of ABA-hypersensitive mutants is known, however, only a few of them resist/avoid drought stress. In this work we have generated ABA-hypersensitive drought-avoidant mutants by simultaneous inactivation of two negative regulators of ABA signaling, i.e. the protein phosphatases type 2C (PP2Cs) ABA-INSENSITIVE1 (ABI1) and HYPERSENSITIVE TO ABA1 (HAB1). Two new recessive loss-of-function alleles of ABI1, abi1-2 and abi1-3, were identified in an Arabidopsis (Arabidopsis thaliana) T-DNA collection. These mutants showed enhanced responses to ABA both in seed and vegetative tissues, but only a limited effect on plant drought avoidance. In contrast, generation of double hab1-1 abi1-2 and hab1-1 abi1-3 mutants strongly increased plant responsiveness to ABA. Thus, both hab1-1 abi1-2 and hab1-1 abi1-3 were particularly sensitive to ABA-mediated inhibition of seed germination. Additionally, vegetative responses to ABA were reinforced in the double mutants, which showed a strong hypersensitivity to ABA in growth assays, stomatal closure, and induction of ABA-responsive genes. Transpirational water loss under drought conditions was noticeably reduced in the double mutants as compared to single parental mutants, which resulted in reduced water consumption of whole plants. Taken together, these results reveal cooperative negative regulation of ABA signaling by ABI1 and HAB1 and suggest that fine tuning of ABA signaling can be attained through combined action of PP2Cs. Finally, these results suggest that combined inactivation of specific PP2Cs involved in ABA signaling could provide an approach for improving crop performance under drought stress conditions.
脱落酸（ABA）在植物对非生物胁迫，尤其是干旱胁迫的响应中起关键作用。已知有大量ABA超敏突变体，然而，其中只有少数能抵抗/避免干旱胁迫。在这项研究中，我们通过同时失活ABA信号转导的两个负调控因子，即2C型蛋白磷酸酶（PP2C）ABA不敏感1（ABI1）和对ABA1超敏感（HAB1），培育出了ABA超敏耐旱突变体。在拟南芥T-DNA库中鉴定出了ABI1的两个新的隐性功能丧失等位基因abi1-2和abi1-3。这些突变体在种子和营养组织中对ABA的反应均增强，但对植物耐旱性的影响有限。相比之下，双突变体hab1-1 abi1-2和hab1-1 abi1-3的产生极大地增强了植物对ABA的反应性。因此，hab1-1 abi1-2和hab1-1 abi1-3对ABA介导的种子萌发抑制特别敏感。此外，双突变体中对ABA的营养反应得到增强，在生长测定、气孔关闭和ABA响应基因诱导方面对ABA表现出强烈的超敏感性。与单亲本突变体相比，双突变体在干旱条件下的蒸腾失水明显减少，这导致整株植物的水分消耗降低。综上所述，这些结果揭示了ABI1和HAB1对ABA信号转导的协同负调控，并表明通过PP2C的联合作用可以实现对ABA信号转导的精细调节。最后，这些结果表明，同时失活参与ABA信号转导的特定PP2C可为改善干旱胁迫条件下作物的性能提供一种方法。
