Photorespiration: origins and metabolic integration in interacting compartments
Photorespiration: origins and metabolic integration in interacting compartments
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DOI：
10.1093/jxb/erw178
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发表时间：
2016-05-13
影响因子：
6.9
通讯作者：
Eisenhut M
中科院分区：
文献类型：
--
作者：
Hagemann M;Weber AP;Eisenhut M
光呼吸的这个特殊问题集中在这个主题的最新进展。大多数论文总结并扩展了2015年6月在德国瓦尔内明德举行的第二次研讨会“光呼吸--作物改良的关键”的贡献。这是由DFG（德国研究基金会）支持的研究网络“光呼吸：相互作用区室中的起源和代谢整合”（FOR 1186-Promics）组织的。术语光呼吸（PR）描述了一种光诱导的生化过程，将2-磷酸乙醇酸（2 PG）转化为3-磷酸甘油酸（3 PGA），并伴有O2吸收和CO2释放。它与光合CO2同化密切相关，是大多数植物碳代谢的主要途径之一。物质流仅次于光合作用，PR实际上构成了陆地生物圈中第二个最重要的过程。利用最广泛的C3类型的光合作用进行CO2同化的植物显示出特别大量的光呼吸CO2产生。PR是通过O2与CO2在通用羧化酶1，5-二磷酸核酮糖羧化酶/加氧酶（Rubisco）（Smith，1976）的活性位点处的竞争而启动的，其在白天产生大量2 PG。因此，PR基本上充当将有毒副产物2 PG转化为有用的Calvin-Benson循环中间体3 PGA的补救或代谢修复过程。它被认为是最重要的古代辅助代谢过程，使植物能够在含O2的大气中茁壮成长（Osmond，1981）。为了将2 PG转化为3 PGA，许多质体、过氧化物酶体、线粒体和胞质酶的协同作用是必要的，这使得该途径成为高等植物亚细胞代谢整合的最突出的例子。然而，PR也导致相当大部分的新鲜同化的C和N作为光呼吸CO2和NH3损失。定量地说，PR可以在当前大气CO2和O2浓度下使光合作用降低高达30%，并且在升高的温度下甚至更多（例如Sharkey，1988; Zhu等人，2004年）。这种净光合作用的显著降低导致了有些误导的观点，即PR是限制C3植物光合生产力的“浪费”过程（例如，加勒特，1978; Siedow和Day，2001）。然而，遗传分析表明PR对于进行产氧光合作用的所有生物体是必需的，因为编码关键光呼吸酶的基因的突变总是导致光呼吸表型并且经常导致致死性（萨默维尔，2001），即蓝细菌、红藻的相应突变体（Rademacher et al.，这一问题），绿藻、C3和C4植物在环境空气中不能存活，只能在人工提高的CO2/O2比率下拯救（综述于Bauwe等人，2010年）。然而，由于大量的CO2和能量损失，PR被视为育种更高产作物的有希望的目标（Ort等人，2015年）。例如，已经开始尝试引入光呼吸旁路以使该过程对能量的需求更少或减少CO2释放（在Peterhänsel等人，2013年）。有趣的是，最近有报道说，而不是减少PR的PR通量能力的增加，导致在环境空气中的拟南芥的生长增强。线粒体甘氨酸切割系统的两种不同蛋白质的独立过表达增加了光呼吸碳流，也提高了Calvin-Benson循环活性，导致更高的光合活性和更高的生物量。
This special issue on photorespiration focuses on recent advances in this topic. The majority of the papers summarizes and extends contributions given at the 2nd workshop,‘Photorespiration–key to better crops’, held in Warnemuende, Germany in June 2015. This was organized by the DFG (German Research Foundation)-supported research network,‘Photorespiration: origins and metabolic integration in interacting compartments’(FOR 1186–Promics). The term photorespiration (PR) describes a light-induced biochemical process that converts 2-phosphoglycolate (2PG) into 3-phosphoglycerate (3PGA) and is accompanied by O2 uptake and CO2 release. It is closely associated with photosynthetic CO2 assimilation and represents one of the major highways of carbon metabolism in most plants. By mass flow, surpassed only by photosynthesis, PR actually constitutes the second most important process in the land-based biosphere. Plants using the most widespread C3 type of photosynthesis for CO2 assimilation display particularly massive photorespiratory CO2 production. PR is initiated by competition of O2 with CO2 at the active site of the universal carboxylating enzyme Ribulose 1, 5-bisphosphate Carboxylase/Oxygenase (Rubisco)(Smith, 1976), which produces large amounts of 2PG during the day. Hence, PR essentially acts as a salvage or metabolic repair process that converts the toxic by-product 2PG into the useful Calvin–Benson cycle intermediate 3PGA. It is supposedly the most important ancient ancillary metabolic process that enables plants to thrive in an O2-containing atmosphere (Osmond, 1981). To convert 2PG into 3PGA, the concerted action of many plastidial, peroxisomal, mitochondrial, and also cytosolic enzymes is necessary, which makes this pathway the most prominent example of subcellular metabolic integration in higher plants.However, PR also leads to the loss of a considerable fraction of freshly assimilated C and N as photorespiratory CO2 and NH3. Quantitatively, PR can decrease photosynthesis by up to 30% under current atmospheric concentrations of CO2 and O2 and even more at elevated temperature (eg Sharkey, 1988; Zhu et al., 2004). This substantial decrease of net photosynthesis led to the somewhat misleading view of PR as a ‘wasteful’process limiting photosynthetic productivity in C3 plants (eg Garrett, 1978; Siedow and Day, 2001). However, genetic analysis showed that PR is essential for all organisms performing oxygenic photosynthesis, since mutations of genes encoding for key photorespiratory enzymes always resulted in the photorespiratory phenotype and frequently in lethality (Somerville, 2001), ie corresponding mutants of cyanobacteria, red algae (Rademacher et al., this issue), chlorophytes, C3 and C4 plants were not viable in ambient air and could only be rescued under artificially enhanced CO2/O2 ratios (reviewed in Bauwe et al., 2010). Nevertheless, due to the large CO2 and energy losses, PR is seen as a promising target in breeding more productive crops (Ort et al., 2015). For example, attempts have been initiated to introduce photorespiratory bypasses to make the process less energy demanding or to reduce the CO2 release (reviewed in Peterhänsel et al., 2013). Interestingly, it has recently been reported that, instead of decreasing PR an increased PR flux capacity resulted in enhanced growth of Arabidopsis thaliana in ambient air. The independent over-expression of two different proteins of the mitochondrial glycine cleavage system increased photorespiratory carbon flow and also improved Calvin–Benson cycle activity, leading to higher photosynthetic activity and higher biomass …