Department of Cell and Systems Biology, University of Toronto, Toronto, Ontario M5S 3B2, Canada.
Plant Physiol. 2010 Apr;152(4):1901-13. doi: 10.1104/pp.109.152603. Epub 2010 Feb 17.
A number of Arabidopsis (Arabidopsis thaliana) lesion-mimic mutants exhibit alterations in both abiotic stress responses and pathogen resistance. One of these mutants, constitutive expresser of PR genes22 (cpr22), which has a mutation in two cyclic nucleotide-gated ion channels, is a typical lesion-mimic mutant exhibiting elevated levels of salicylic acid (SA), spontaneous cell death, constitutive expression of defense-related genes, and enhanced resistance to various pathogens; the majority of its phenotypes are SA dependent. These defense responses in cpr22 are suppressed under high-humidity conditions and enhanced by low humidity. After shifting plants from high to low humidity, the cpr22 mutant, but not the wild type, showed a rapid increase in SA levels followed by an increase in abscisic acid (ABA) levels. Concomitantly, genes for ABA metabolism were up-regulated in the mutant. The expression of a subset of ABA-inducible genes, such as RD29A and KIN1/2, was down-regulated, but that of other genes, like ABI1 and HAB1, was up-regulated in cpr22 after the humidity shift. cpr22 showed reduced responsiveness to ABA not only in abiotic stress responses but also in germination and stomatal closure. Double mutant analysis with nahG plants that degrade SA indicated that these alterations in ABA signaling were attributable to elevated SA levels. Furthermore, cpr22 displayed suppressed drought responses by long-term drought stress. Taken together, these results suggest an effect of SA on ABA signaling/abiotic stress responses during the activation of defense responses in cpr22.
拟南芥（Arabidopsis thaliana）的许多病变模拟突变体在非生物胁迫反应和病原体抗性方面都发生了改变。这些突变体之一，即组成型表达 PR 基因 22（cpr22），它在两个环核苷酸门控离子通道中发生突变，是一个典型的病变模拟突变体，表现为水杨酸（SA）水平升高、自发性细胞死亡、防御相关基因的组成型表达和对各种病原体的增强抗性；其大多数表型均依赖于 SA。在高湿度条件下，cpr22 中的这些防御反应受到抑制，而在低湿度下则增强。将植物从高湿度转移到低湿度后，cpr22 突变体而非野生型表现出 SA 水平的快速增加，随后 ABA（脱落酸）水平增加。同时，突变体中 ABA 代谢基因上调。ABA 诱导基因的一部分，如 RD29A 和 KIN1/2 的表达下调，但在湿度变化后，ABI1 和 HAB1 等其他基因的表达在 cpr22 中上调。cpr22 不仅在非生物胁迫反应中，而且在萌发和气孔关闭中对 ABA 的反应性降低。与降解 SA 的 nahG 植物的双突变体分析表明，ABA 信号的这些改变归因于 SA 水平的升高。此外，cpr22 在长期干旱胁迫下显示出对干旱反应的抑制。综上所述，这些结果表明在 cpr22 中防御反应的激活过程中，SA 对 ABA 信号/非生物胁迫反应有影响。
