Post-Translational Derepression of Invertase Activity in Source Leaves via Down-Regulation of Invertase Inhibitor Expression Is Part of the Plant Defense Response
Post-Translational Derepression of Invertase Activity in Source Leaves via Down-Regulation of Invertase Inhibitor Expression Is Part of the Plant Defense Response
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DOI：
10.1093/mp/ssq053
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发表时间：
2010-11-01
期刊：
影响因子：
27.5
通讯作者：
Roitsch, Thomas
中科院分区：
文献类型：
--
作者：
Bonfig, Katharina B.;Gabler, Andrea;Roitsch, Thomas
越来越多的证据表明，病原体不仅引起直接的防御反应，而且还引起初级碳水化合物代谢的显著变化。细胞壁结合型转化酶是调节碳水化合物分配和源库关系的关键酶。然而，迄今为止的研究只集中在转化酶基因的转录诱导响应病原体感染，转化酶活性的翻译后调节的作用被忽视，是本研究的重点。表达分析表明，高mRNA水平的三个蛋白质转化酶抑制剂在源叶拟南芥强烈抑制感染后，假单胞菌pv.番茄DC3000。这种抑制被转化酶抑制剂活性的降低所抵消。这一调节机制的生理作用是通过发现原位转化酶活性仅在感染P.dichloringae后才可检测到而揭示的。与此相反，高转化酶活性可以在体外测定的粗品和细胞壁提取物从感染和未感染的叶子。原位和体外转化酶活性的控制叶片和高原位转化酶活性在感染的叶片之间的差异可以解释由病原体依赖的抑制转化酶抑制剂的表达和伴随的转化酶抑制剂活性的减少。转化酶从翻译后抑制释放对防御反应的功能重要性通过竞争性转化酶抑制剂阿卡波糖的应用得到证实。通过阿卡波糖在叶片中的渗透来抑制细胞外转化酶活性的翻译后抑制被证明增加了对P. degeneriae的敏感性。转化酶抑制对光合作用抑制和病原体感染期间细菌生长促进的时空动态的影响支持胞外转化酶在植物防御中的作用。阿卡波糖介导的易感性增加也可在cpr2和cpr6突变体中检测到，并导致水杨酸水平略微升高，表明该效应不依赖于水杨酸调节的防御途径。这些研究结果提供了一个解释高提取转化酶活性源叶保持原位抑制转化酶和转化酶抑制剂蛋白之间的翻译后相互作用。在病原体感染时，转化酶活性通过抑制转化酶抑制剂表达而释放，从而将库强度的局部诱导与植物防御反应联系起来。
There is increasing evidence that pathogens do not only elicit direct defense responses, but also cause pronounced changes in primary carbohydrate metabolism. Cell-wall-bound invertases belong to the key regulators of carbohydrate partitioning and source-sink relations. Whereas studies have focused so far only on the transcriptional induction of invertase genes in response to pathogen infection, the role of post-translational regulation of invertase activity has been neglected and was the focus of the present study. Expression analyses revealed that the high mRNA level of one out of three proteinaceous invertase inhibitors in source leaves of Arabidopsis thaliana is strongly repressed upon infection by a virulent strain of Pseudomonas syringae pv. tomato DC3000. This repression is paralleled by a decrease in invertase inhibitor activity. The physiological role of this regulatory mechanism is revealed by the finding that in situ invertase activity was detectable only upon infection by P. syringae. In contrast, a high invertase activity could be measured in vitro in crude and cell wall extracts prepared from both infected and non-infected leaves. The discrepancy between the in situ and in vitro invertase activity of control leaves and the high in situ invertase activity in infected leaves can be explained by the pathogen-dependent repression of invertase inhibitor expression and a concomitant reduction in invertase inhibitor activity. The functional importance of the release of invertase from post-translational inhibition for the defense response was substantiated by the application of the competitive chemical invertase inhibitor acarbose. Post-translational inhibition of extracellular invertase activity by infiltration of acarbose in leaves was shown to increase the susceptibility to P. syringae. The impact of invertase inhibition on spatial and temporal dynamics of the repression of photosynthesis and promotion of bacterial growth during pathogen infection supports a role for extracellular invertase in plant defense. The acarbose-mediated increase in susceptibility was also detectable in sid2 and cpr6 mutants and resulted in slightly elevated levels of salicylic acid, demonstrating that the effect is independent of the salicylic acid-regulated defense pathway. These findings provide an explanation for high extractable invertase activity found in source leaves that is kept inhibited in situ by post-translational interaction between invertase and the invertase inhibitor proteins. Upon pathogen infection, the invertase activity is released by repression of invertase inhibitor expression, thus linking the local induction of sink strength to the plant defense response.