Dipartimento di Biotecnologie, Università di Verona, Strada Le Grazie 15, Verona, Italy.
BMC Plant Biol. 2011 Apr 11;11:62. doi: 10.1186/1471-2229-11-62.
Reactive oxygen species (ROS) are unavoidable by-products of oxygenic photosynthesis, causing progressive oxidative damage and ultimately cell death. Despite their destructive activity they are also signalling molecules, priming the acclimatory response to stress stimuli.
To investigate this role further, we exposed wild type Arabidopsis thaliana plants and the double mutant npq1lut2 to excess light. The mutant does not produce the xanthophylls lutein and zeaxanthin, whose key roles include ROS scavenging and prevention of ROS synthesis. Biochemical analysis revealed that singlet oxygen (1O2) accumulated to higher levels in the mutant while other ROS were unaffected, allowing to define the transcriptomic signature of the acclimatory response mediated by 1O2 which is enhanced by the lack of these xanthophylls species. The group of genes differentially regulated in npq1lut2 is enriched in sequences encoding chloroplast proteins involved in cell protection against the damaging effect of ROS. Among the early fine-tuned components, are proteins involved in tetrapyrrole biosynthesis, chlorophyll catabolism, protein import, folding and turnover, synthesis and membrane insertion of photosynthetic subunits. Up to now, the flu mutant was the only biological system adopted to define the regulation of gene expression by 1O2. In this work, we propose the use of mutants accumulating 1O2 by mechanisms different from those activated in flu to better identify ROS signalling.
We propose that the lack of zeaxanthin and lutein leads to 1O2 accumulation and this represents a signalling pathway in the early stages of stress acclimation, beside the response to ADP/ATP ratio and to the redox state of both plastoquinone pool. Chloroplasts respond to 1O2 accumulation by undergoing a significant change in composition and function towards a fast acclimatory response. The physiological implications of this signalling specificity are discussed.
活性氧（ROS）是需氧光合作用不可避免的副产物，导致渐进性氧化损伤并最终导致细胞死亡。尽管它们具有破坏性的作用，但它们也是信号分子，为适应应激刺激的反应做好准备。
为了进一步研究这个角色，我们将野生型拟南芥和 npq1lut2 双突变体暴露在过量的光下。突变体不能产生叶黄素和玉米黄质等叶黄素，其关键作用包括清除活性氧和防止活性氧的合成。生化分析表明，单线态氧（1O2）在突变体中积累到更高水平，而其他活性氧不受影响，从而定义了由 1O2 介导的适应反应的转录组特征，这种特征因缺乏这些叶黄素而增强。在 npq1lut2 中差异调节的基因组富含编码参与叶绿体蛋白的序列，这些蛋白可保护细胞免受 ROS 的破坏性影响。在早期精细调整的成分中，包括参与四吡咯生物合成、叶绿素分解、蛋白导入、折叠和周转、光合亚基合成和膜插入的蛋白质。到目前为止，flu 突变体是唯一被采用来定义 1O2 对基因表达调控的生物系统。在这项工作中，我们提出使用通过与 flu 中激活的机制不同的机制积累 1O2 的突变体，以更好地识别 ROS 信号。
我们提出，玉米黄质和叶黄素的缺乏导致 1O2 的积累，这代表了应激适应早期阶段的信号通路，除了对 ADP/ATP 比值和质体醌库的氧化还原状态的反应之外。叶绿体通过在组成和功能上发生显著变化来应对 1O2 的积累，从而快速适应。讨论了这种信号特异性的生理意义。
