Abstract
The plastid ndh genes have hovered frequently on the edge of dispensability. They are absent in the plastid DNA of many algae and certain higher plants and present editing sites requiring C-to-U corrections of primary transcripts. The evolutionary origin of editing sites and their loss due to C-to-T reversions at the DNA level are unknown and must be related to the dispensability of the ndh genes in specific environments. In order to better understand the evolution of ndh gene editing sites, we have created expandable data banks with the 12 editing sites of the ndhB gene (600 GenBank sequences) and both editing sites of the ndhF gene (1,600 GenBank sequences). Since their origin via T-to-C mutations that probably occurred between 300 and 200 Myr BP (Permian-Triassic), ndh editing sites have undergone independent and random C-to-T reversions in the different angiosperm lineages. Some of these reversions appear early in angiosperm diversification. Old C-to-T reversions can be traced back to radiation steps that gave origin to main classes, orders and some families.
Highlights
The plastid ndh genes encode 11 NDH polypeptides of the thylakoid Ndh complex (Maier et al, 1995; Sazanov et al, 1998; Casano et al, 2000; Yukawa et al, 2005) analogous to the mitochondrial complex I (EC 1.6.5.3)
C-to-T Reversions at the DNA Level of the Editing Sites of ndhB and ndhF Plastid Genes in Seed Plants The comparison of genomic and complementary sequences to mRNA in several plants such as Nicotiana tabacum, Arabidopsis thaliana, Zea mays, and Hordeum vulgare, confirmed the existence of 12 and two editing sites in the mature transcripts of the ndhB and ndhF genes, respectively, in angiosperms (Freyer et al, 1995, 1997; Maier et al, 1995; Tillich et al, 2005; Martín and Sabater, 2010)
Each species has a different set of editing sites due to the fact that certain Cs are substituted by Ts at the DNA level in the other potential sites or because, as occurs with the B-10 site, the C is posttranscriptionally edited to U in Arabidopsis thaliana and other Brassicaceae, but not in other angiospems
Summary
The plastid ndh genes encode 11 NDH polypeptides of the thylakoid Ndh complex (Maier et al, 1995; Sazanov et al, 1998; Casano et al, 2000; Yukawa et al, 2005) analogous to the mitochondrial complex I (EC 1.6.5.3). The Ndh complex catalyzes the transfer of electrons from NADH to plastoquinone, the first stage of the chlororespiratory reaction chain in which the Mehler reaction, superoxide dismutase and peroxidase activities drain excess electrons to fine-tune the redox level of the cyclic electron transporters (Casano et al, 2000; Rumeau et al, 2007; Martín et al, 2009, 2015) According to this function, the ndh genes are required to optimize photosynthesis rate under fluctuating light and high CO2 concentrations (Martín et al, 2009, 2015). These particular species may contain ndh gene fragments in either the nucleus or mitochondrion, which suggests that ndh genes could be dispensable in some plants and/or environments
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