Department of Biophysics, Centre of the Region Haná for Biotechnological and Agricultural Research, Palacký University, 783 71, Olomouc, Czech Republic.
Department of Biology, University of Padova, 35131, Padova, Italy.
New Phytol. 2017 May;214(3):967-972. doi: 10.1111/nph.14536. Epub 2017 Mar 17.
Photo-reduction of O to water mediated by flavodiiron proteins (FDPs) represents a safety valve for the photosynthetic electron transport chain in fluctuating light. So far, the FDP-mediated O photo-reduction has been evidenced only in cyanobacteria and the moss Physcomitrella; however, a recent phylogenetic analysis of transcriptomes of photosynthetic organisms has also revealed the presence of FDP genes in several nonflowering plant groups. What remains to be clarified is whether the FDP-dependent O photo-reduction is actually operational in these organisms. We have established a simple method for the monitoring of FDP-mediated O photo-reduction, based on the measurement of redox kinetics of P700 (the electron donor of photosystem I) upon dark-to-light transition. The O photo-reduction is manifested as a fast re-oxidation of P700. The validity of the method was verified by experiments with transgenic organisms, namely FDP knock-out mutants of Synechocystis and Physcomitrella and transgenic Arabidopsis plants expressing FDPs from Physcomitrella. We observed the fast P700 re-oxidation in representatives of all green plant groups excluding angiosperms. Our results provide strong evidence that the FDP-mediated O photo-reduction is functional in all nonflowering green plant groups. This finding suggests a major change in the strategy of photosynthetic regulation during the evolution of angiosperms.
类铁黄素蛋白（FDPs）介导的 O 向水的光还原代表了光合电子传递链在波动光下的安全阀。到目前为止，FDP 介导的 O 光还原仅在蓝藻和苔藓 Physcomitrella 中得到证实；然而，最近对光合生物转录组的系统发育分析也揭示了几个非开花植物群中存在 FDP 基因。仍有待澄清的是，在这些生物体中，FDP 依赖性 O 光还原是否实际上是可行的。我们已经建立了一种简单的方法来监测 FDP 介导的 O 光还原，该方法基于在黑暗到光照转换时测量 P700（光系统 I 的电子供体）的氧化还原动力学。O 光还原表现为 P700 的快速再氧化。该方法的有效性通过转基因生物的实验得到了验证，即 Synechocystis 和 Physcomitrella 的 FDP 敲除突变体以及表达来自 Physcomitrella 的 FDP 的转基因拟南芥植物。我们观察到所有绿色植物群（除被子植物外）的 P700 快速再氧化。我们的结果提供了强有力的证据表明，FDP 介导的 O 光还原在所有非开花绿色植物群中都是功能性的。这一发现表明，在被子植物进化过程中，光合调节策略发生了重大变化。
