Jirage D, Tootle T L, Reuber T L, Frost L N, Feys B J, Parker J E, Ausubel F M, Glazebrook J
Molecular and Cell Biology Graduate Program, University of Maryland, College Park, MD 20742, USA.
Proc Natl Acad Sci U S A. 1999 Nov 9;96(23):13583-8. doi: 10.1073/pnas.96.23.13583.
The Arabidopsis PAD4 gene previously was found to be required for expression of multiple defense responses including camalexin synthesis and PR-1 gene expression in response to infection by the bacterial pathogen Pseudomonas syringae pv. maculicola. This report describes the isolation of PAD4. The predicted PAD4 protein sequence displays similarity to triacyl glycerol lipases and other esterases. The PAD4 transcript was found to accumulate after P. syringae infection or treatment with salicylic acid (SA). PAD4 transcript levels were very low in infected pad4 mutants. Treatment with SA induced expression of PAD4 mRNA in pad4-1, pad4-3, and pad4-4 plants but not in pad4-2 plants. Induction of PAD4 expression by P. syringae was independent of the regulatory factor NPR1 but induction by SA was NPR1-dependent. Taken together with the previous observation that pad4 mutants have a defect in accumulation of SA upon pathogen infection, these results suggest that PAD4 participates in a positive regulatory loop that increases SA levels, thereby activating SA-dependent defense responses.
先前发现拟南芥PAD4基因是多种防御反应表达所必需的，这些防御反应包括响应细菌性病原菌丁香假单胞菌番茄致病变种的感染而合成植保素以及PR-1基因的表达。本报告描述了PAD4的分离。预测的PAD4蛋白序列与三酰甘油脂肪酶和其他酯酶具有相似性。发现PAD4转录本在丁香假单胞菌感染或用水杨酸（SA）处理后积累。在受感染的pad4突变体中，PAD4转录水平非常低。用SA处理可诱导pad4-1、pad4-3和pad4-4植株中PAD4 mRNA的表达，但不能诱导pad4-2植株中PAD4 mRNA的表达。丁香假单胞菌对PAD4表达的诱导不依赖于调节因子NPR1，但SA对其诱导是依赖于NPR1的。结合先前观察到的pad4突变体在病原体感染时SA积累存在缺陷，这些结果表明PAD4参与了一个正调控环，该调控环增加SA水平，从而激活依赖SA的防御反应。
