Ishikawa Noriko, Takabayashi Atsushi, Ishida Satoshi, Hano Yasushi, Endo Tsuyoshi, Sato Fumihiko
Graduate School of Biostudies, Kyoto University, Sakyoku, Kyoto, 606-8502 Japan.
Plant Cell Physiol. 2008 Jul;49(7):1066-73. doi: 10.1093/pcp/pcn083. Epub 2008 Jun 4.
NAD(P)H dehydrogenase (NDH) is a homolog of respiratory complex I and mediates one of the two pathways of cyclic electron flow around PSI (CEF I). Although 15 ndh subunits have been identified in the chloroplastic and nuclear genomes of higher plants, no electron accepter subunits have been identified to date. To identify the missing chloroplastic NDH subunits, we undertook an in silico approach based on co-expression analysis. In this report, we characterized the novel gene NDF6 (NDH-dependent flow 6; At1g18730) which encodes a protein that is essential for NDH activity. NDF6 has one transmembrane domain and is localized in the thylakoid membrane fraction. Homologous proteins of NDF6 were identified in the genomes of terrestrial plants; however, no homologs have been found in cyanobacteria, which are thought to be the origin of chloroplasts and have a minimal NDH complex unit. NDF6 is unstable in ndhB-impaired or disrupted mutants of higher plants in which the chloroplastic NDH complex is thought to be degraded. These results suggest that NDF6 is a novel subunit of chloroplastic NDH that was added to terrestrial plants during evolution.
NAD(P)H脱氢酶（NDH）是呼吸复合体I的同源物，介导围绕光系统I的循环电子流（CEF I）的两条途径之一。尽管在高等植物的叶绿体和核基因组中已鉴定出15个ndh亚基，但迄今为止尚未鉴定出电子受体亚基。为了鉴定缺失的叶绿体NDH亚基，我们基于共表达分析采用了一种计算机模拟方法。在本报告中，我们对新基因NDF6（NDH依赖性流6；At1g18730）进行了表征，该基因编码一种对NDH活性至关重要的蛋白质。NDF6有一个跨膜结构域，定位于类囊体膜部分。在陆生植物基因组中鉴定出了NDF6的同源蛋白；然而，在被认为是叶绿体起源且具有最小NDH复合体单元的蓝细菌中未发现同源物。在叶绿体NDH复合体被认为会降解的高等植物的ndhB受损或破坏的突变体中，NDF6不稳定。这些结果表明，NDF6是叶绿体NDH的一个新亚基，是在进化过程中添加到陆生植物中的。
