抑制AtCLH1表达降低叶片衰老进程中叶绿素a与b的比值但不影响叶绿素降解速率(英文)

Repression of AtCLH1 Expression Results in a Decrease in the Ratio of Chlorophyll a/b but Doesn't Affect the Rate of Chlorophyll Degradation during Leaf Senescence

为了分析叶绿素酶在叶绿素降解过程中的作用,构建了抑制AtCLH1和/或AtCLH2的拟南芥RNAi株系。在RNAi株系中,叶绿素酶的表达和活性都被显著抑制。然而,无论是在正常生长情况下还是在黑暗诱导的衰老进程中,RNAi株系中的叶绿素降解速率与野生型中的相比均无显著差异。进一步的分析结果表明,AtCLH1 RNAi株系中的叶绿素a/b比值在叶片衰老进程中逐渐降低,而野生型中的却逐渐升高。另外,还观察到所有株系中叶绿素酶的活性在黑暗诱导的衰老过程的初期均呈现出上升的趋势。与这一变化趋势正好相反,在所有株系中,叶绿素酶基因的表达在黑暗诱导衰老后就开始大幅下降。有趣的是,与野生型相比,RNAi株系中的目标叶绿素酶基因仍然维持在一个较低的表达水平。这说明拟南芥中可能存在一个反馈补偿机制。基于这些结果,并结合相关的研究报道,认为叶绿素酶很可能参与了衰老进程早期的叶绿素b向a的转换过程。

To explore the possible regulatory role of chlorophyllase （Chlase） in chlorophyll （Chl） degradation during leaf senescence, RNAi Arabidopsis （Arabidopsis thaliana） plants were constructed to repress the expressions of AtCLH1 and/or AtCLH2. Transcript levels of AtCLH1 and/or AtCLH2 were dramatically lowered and Chlase activity was correspondingly inhibited, but the Chl degradation kinetics was not affected in the RNAi plants. Results of further analysis indicated that the Chl a/b ratio decreased in AtCLH1 RNAi lines, in comparison with the increasing Chl a/b ratio in the wide type during leaf senescence. In addition, an induced Chlase activity was consistently detected at the initial stage of senescence in all the plants examined. In contrast, transcript levels of both AtCLH1 and AtCLH2 decreased dramatically upon the initiation of senescence in both the wide-type and the RNAi plants. Interestingly, compared with the wide type, lower but still significant transcript levels of the RNAi targeted Chlase gene（s） were sustained during the whole period of dark incubation in all the three RNAi lines examined, indicating the functioning of some compensatively regulating mechanism Based on these results, along with related reports, we conclude that Chlase might be required at the initial stage of leaf senescence, quite likely playing a role in converting Chl btoa.