Differential Operation of Dual Protochlorophyllide Reductases for Chlorophyll Biosynthesis in Response to Environmental Oxygen Levels in the Cyanobacterium Leptolyngbya boryana1
Differential Operation of Dual Protochlorophyllide Reductases for Chlorophyll Biosynthesis in Response to Environmental Oxygen Levels in the Cyanobacterium Leptolyngbya boryana1
复制标题
DOI：
10.1104/pp.106.086090
复制
发表时间：
2006-10
期刊：
影响因子：
7.4
通讯作者：
S. Yamazaki;Jiro Nomata;Y. Fujita
中科院分区：
文献类型：
--
作者：
S. Yamazaki;Jiro Nomata;Y. Fujita
大多数产氧光养生物，包括蓝细菌，在叶绿素生物合成的倒数第二步中具有两种结构上不相关的原叶绿素内酯（Pchlide）还原酶。一种是光依赖性 Pchlide 还原酶 (LPOR)，另一种是暗操作 Pchlide 还原酶 (DPOR)，一种被认为对氧敏感的固氮酶样酶。关于氧敏感 DPOR 如何在氧光养细胞中发挥作用的研究很少。在这里，我们报告说，DPOR 需要厌氧条件来补偿蓝藻细胞中 LPOR 的损失。蓝藻 Leptolyngbya boryana（以前称为 Plectonema boryanum）的缺乏 LPOR 的突变体无法在强光条件下生长，通过在厌氧条件（2% CO2/N2）下培养可以克服这种表型。使突变体能够在高光下生长的临界氧水平确定为 3% (v/v)。在厌氧生长的突变体的无细胞提取物中，氧敏感的 Pchlide 还原活性被成功检测为 DPOR 活性，而在野生型中检测不到该活性。与野生型相比，突变细胞中两个DPOR亚基ChlL和ChlN的含量显着增加。这表明亚基的增加刺激了 DPOR 活性，该活性通过厌氧环境有效地免受氧气的影响，从而补充了 LPOR 的损失。这些结果为理解双 Pchlide 还原酶如何在氧水平发生动态变化的自然环境下生长的含氧光合细胞中差异运作提供了重要的概念。讨论了两种 Pchlide 还原酶共存的进化意义。
Most oxygenic phototrophs, including cyanobacteria, have two structurally unrelated protochlorophyllide (Pchlide) reductases in the penultimate step of chlorophyll biosynthesis. One is light-dependent Pchlide reductase (LPOR) and the other is dark-operative Pchlide reductase (DPOR), a nitrogenase-like enzyme assumed to be sensitive to oxygen. Very few studies have been conducted on how oxygen-sensitive DPOR operates in oxygenic phototrophic cells. Here, we report that anaerobic conditions are required for DPOR to compensate for the loss of LPOR in cyanobacterial cells. An LPOR-lacking mutant of the cyanobacterium Leptolyngbya boryana (formerly Plectonema boryanum) failed to grow in high light conditions and this phenotype was overcome by cultivating it under anaerobic conditions (2% CO2/N2). The critical oxygen level enabling the mutant to grow in high light was determined to be 3% (v/v). Oxygen-sensitive Pchlide reduction activity was successfully detected as DPOR activity in cell-free extracts of anaerobically grown mutants, whereas activity was undetectable in the wild type. The content of two DPOR subunits, ChlL and ChlN, was significantly increased in mutant cells compared with wild type. This suggests that the increase in subunits stimulates the DPOR activity that is protected efficiently from oxygen by anaerobic environments, resulting in complementation of the loss of LPOR. These results provide important concepts for understanding how dual Pchlide reductases operate differentially in oxygenic photosynthetic cells grown under natural environments where oxygen levels undergo dynamic changes. The evolutionary implications of the coexistence of two Pchlide reductases are discussed.