Department of Botany, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan CREST, Japan.
Plant J. 2012 Nov;72(4):683-93. doi: 10.1111/j.1365-313X.2012.05115.x. Epub 2012 Sep 24.
The chloroplast NADH dehydrogenase-like (NDH) complex mediates cyclic electron transport and chloro-respiration and consists of five sub-omplexes, which in angiosperms further associate with photosystem I (PSI) to form a super-complex. In Marchantia polymorpha, 11 plastid-encoded subunits and all the nuclear-encoded subunits of the A, B, membrane and ferredoxin-binding sub-complexes are conserved. However, it is unlikely that the genome of this liverwort encodes Lhca5 and Lhca6, both of which mediate NDH-PSI super-complex formation. It is also unlikely that the subunits of the lumen sub-complex, PnsL1-L4, are encoded by the genome. Consistent with this in silico prediction, the results of blue-native gel electrophoresis showed that NDH subunits were detected in a protein complex with lower molecular mass in Marchantia than the NDH-PSI super-complex in Arabidopsis. Using the plastid transformation technique, we knocked out the ndhB gene in Marchantia. Although the wild-type genome copies were completely segregated out, the ΔndhB lines grew like the wild-type photoautotrophically. A post-illumination transient increase in chlorophyll fluorescence, which reflects NDH activity in vivo in angiosperms, was absent in the thalli of the ΔndhB lines. In ruptured chloroplasts, antimycin A-insensitive, and ferredoxin-dependent plastoquinone reduction was impaired, suggesting that chloroplast NDH mediates similar electron transport in Marchantia and Arabidopsis, despite its possible difference in structure. As in angiosperms, linear electron transport was not strongly affected in the ΔndhB lines. However, the plastoquinone pool was slightly more reduced at low light intensity, suggesting that chloroplast NDH functions in redox balancing of the inter system, especially under low light conditions.
叶绿体 NADH 脱氢酶样（NDH）复合物介导环式电子传递和氯呼吸，由五个亚复合物组成，在被子植物中，这些亚复合物进一步与光系统 I（PSI）结合形成超复合物。在 Marchantia polymorpha 中，11 个质体编码亚基和 A、B、膜和铁氧还蛋白结合亚复合物的所有核编码亚基都被保守。然而，这种苔藓植物的基因组不太可能编码 Lhca5 和 Lhca6，这两种蛋白都介导 NDH-PSI 超复合物的形成。也不太可能编码腔亚复合物的亚基 PnsL1-L4 是由基因组编码的。与这种计算机预测一致，蓝Native 凝胶电泳的结果表明，在 Marchantia 中，NDH 亚基在与 Arabidopsis 中的 NDH-PSI 超复合物相比分子量较低的蛋白质复合物中被检测到。利用质体转化技术，我们敲除了 Marchantia 中的 ndhB 基因。尽管野生型基因组拷贝完全被分离出来，但 ΔndhB 系像野生型光自养生物一样生长。在光照后的短暂时间内，叶绿素荧光的增加反映了被子植物体内 NDH 的活性，但在 ΔndhB 系的组织中却没有。在破裂的叶绿体中，抗霉素 A 不敏感和铁氧还蛋白依赖性质体醌还原受损，这表明尽管结构可能不同，但质体 NDH 在 Marchantia 和 Arabidopsis 中介导类似的电子传递。与被子植物一样，在 ΔndhB 系中线性电子传递没有受到强烈影响。然而，在低光强度下，质体醌库稍微还原，这表明质体 NDH 在光合作用系统之间的氧化还原平衡中起作用，特别是在低光条件下。
