Deletion of the last two exons of the mitochondrialnad7 gene results in lack of the NAD7 polypeptide in aNicotiana sylvestris CMS mutant

Abstract

In Nicotiana sylvestris, two cytoplasmic male sterile (CMS) mutants obtained by protoplast culture show abnormal developmental features of both vegetative and reproductive organs, and mitochondrial gene reorganization following homologous recombination between 65 bp repeated sequences. A mitochondrial region of 16.2 kb deleted from both CMS mutants was found to contain the last two exons of the nad7 gene coding for a subunit of the mitochondrial respiratory chain complex I, which is encoded in the nucleus in fungi and animals but was recently found to be encoded by the mitochondrial genome in wheat. Although the N. sylvestris nad7 gene shows strong homology with its wheat counterpart, it contains only three introns instead of four. Polymerase chain reaction (PCR) experiments indicated that the parental gene organization, including the complete nad7 gene, is probably maintained at a substoichiometric level in the CMS mutants, but this proportion is too low to have a significant physiological role, as confirmed by expression studies showing the lack of detectable amounts of the NAD7 polypeptide. Consequently, absence of NAD7 is not lethal to plant cells but a deficiency of complex I could be involved in the abnormal CMS phenotype.

The Pentatricopeptide Repeat GeneOTP43Is Required fortrans-Splicing of the Mitochondrialnad1Intron 1 inArabidopsis thaliana

“…Two mitochondrial mutants with similar deletions have been described from Nicotiana sylvestris (Pla et al, 1995) and another mitochondrial DNA deletion mutant from maize (Zea mays; Karpova and Newton, 1999). A nuclear mutant almost lacking Complex I was observed in N. sylvestris (Brangeon et al, 2000), while three nuclear mutants affected in Complex I have been identified in Arabidopsis (Lee et al, 2002;Perales et al, 2005;Nakagawa and Sakurai, 2006).…”

“…The best-characterized mutant to date is the CMSII mutant in N. sylvestris. This mutant carries a mitochondrial deletion in the nad7 gene encoding a 40-kD subunit of Complex I (Pla et al, 1995). The mutant plants develop slowly, exhibit conditional male sterility, and have no detectable Complex I, increased amounts and activity of AOX, and multiple perturbations to primary metabolism (Gutierres et al, 1997(Gutierres et al, , 1999Lelandais et al, 1998;Sabar et al, 2000;Dutilleul et al, 2003aDutilleul et al, , 2003bDutilleul et al, , 2005Pineau et al, 2005;Priault et al, 2006aPriault et al, , 2006bVidal et al, 2007).…”

Inactivation of genes coding for mitochondrial Nd7 and Nd9 complex I subunits in Chlamydomonas reinhardtii. Impact of complex I loss on respiration and energetic metabolism

“…Although no structurally intact complex is present in membranes of the nuoC-null mutant, a soluble 170 kD fragment corresponding to the NADH dehydrogenase module (NuoE/NDUFV2/24 kD, NuoF/NDUFV1/51 kD, NuoG/NDUFS1/75 kD) is still active (Erhardt et al, 2012). In tobacco (Nicotiana sylvestris), CMSI/II mutants are impaired in the expression of chloroplastic nad7 gene (Lelandais et al, 1998;Pla et al, 1995). As a consequence, rotenone-sensitive oxygen uptake is decreased and there is no complex I assembly (Gutierres et al, 1997;Pineau et al, 2005).…”

Remodeled Respiration in ndufs4 with Low Phosphorylation Efficiency Suppresses Arabidopsis Germination and Growth and Alters Control of Metabolism at Night

“…For example, deficiency in complex I function has been associated with several human diseases such as Leber's heredity optic neuropathy (Wallace et al, 1988), Leigh syndrome (Hoefs et al, 2008), and leukodystrophy (Holt et al, 1988), and complete absence of complex I is considered lethal. A number of plant mutants lacking respiratory chain components have been studied, including mutants in complex I (Marienfeld and Newton, 1994;Pla et al, 1995;Lee et al, 2002;Perales et al, 2005) and mutants removing specific nonphosphorylating bypasses such as AOX (Giraud et al, 2008). Mutants lacking complex II are embryo lethal in plants (Leon et al, 2007) and mutants lacking complex III or IV have not been reported, presumably as these are lethal in plants, as are mutants in the assembly of c-type cytochromes (Meyer et al, 2005).…”

“…Mutants in genes encoding complex I subunits in Arabidopsis (Arabidopsis thaliana) include the 18-kD subunit (Lee et al, 2002) and the plant-specific CA2 subunit (Perales et al, 2005). Natural mitochondrial mutants lacking some of the mitochondrial nad genes as a result of genome rearrangements have been described in maize (Marienfeld and Newton, 1994) and Nicotiana sylvestris (Pla et al, 1995). Finally, several mutants have been identified in genes encoding splicing factors involved in the expression of nad4 in N. sylvestris (Brangeon et al, 2000) and Arabidopsis (Nakagawa and Sakurai, 2006) and of nad1 in Arabidopsis (de Longevialle et al, 2007).…”