Transcripts of the NADH-dehydrogenase subunit 3 gene are differentially edited in Oenothera mitochondria.

Abstract

A number of cytosines are altered to be recognized as uridines in transcripts of the nad3 locus in mitochondria of the higher plant Oenothera. Such nucleotide modifications can be found at 16 different sites within the nad3 coding region. Most of these alterations in the mRNA sequence change codon identities to specify amino acids better conserved in evolution. Individual cDNA clones differ in their degree of editing at five nucleotide positions, three of which are silent, while two lead to codon alterations specifying different amino acids. None of the cDNA clones analysed is maximally edited at all possible sites, suggesting slow processing or lowered stringency of editing at these nucleotides. Differentially edited transcripts could be editing intermediates or could code for differing polypeptides. Two edited nucleotides in an open reading frame located upstream of nad3 change two amino acids in the deduced polypeptide. Part of the well‐conserved ribosomal protein gene rps12 also encoded downstream of nad3 in other plants, is lost in Oenothera mitochondria by recombination events. The functional rps12 protein must be imported from the cytoplasm since the deleted sequences of this gene are not found in the Oenothera mitochondrial genome. The pseudogene sequence is not edited at any nucleotide position.

Protein Polymorphism Generated by Differential RNA Editing of a Plant Mitochondrial rps12 Gene

“…rps12 genes are found to be cotranscribed with nad3 genes in the mitochondria of several plant species (17,32,36,40). Like rps12 transcripts, nad3 transcripts are also partially edited.…”

“…That RNA editing is a posttranscriptional RNA processing or maturation step is supported by the findings that RNA editing extent correlates temporally with splicing (43,47) and that a single nuclear locus specifies both RNA editing extent and transcript abundance in petunia mitochondria (27). Many transcripts are shown to be partially edited in plant mitochondria (10,17,21,24,27,28,38,40,43,47). In some cases, partially edited transcripts are more abundant than fully edited transcripts (28,40).…”

“…Many transcripts are shown to be partially edited in plant mitochondria (10,17,21,24,27,28,38,40,43,47). In some cases, partially edited transcripts are more abundant than fully edited transcripts (28,40).…”

Ribosomal protein S19 is encoded by the mitochondrial genome in Petunia hybrida

“…The process of RNA editing often changes the amino acid sequence of the proteins encoded by the edited RNA (13,16,17,(22)(23)(24)(25)(26)(27). The seven RNA edits in rpsl9 are shown in Figure 2 as thymidine residues below the genomic sequence.…”

A single homogeneous form of ATP6 protein accumulates in petunia mitochondria despite the presence of differentially edited atp6 transcripts.

“…Unedited transcripts of such genes, such as petunia and wheat ATP synthase subunit 9 (atp9) and wheat cytochrome oxidase subunit 3 (coxlll) and NADH dehydrogenase subunit 4 (nad4), are either extremely low in abundance or complétely undetectable (B6gu et al, 1990;Gualberto et al, 1990;Lamattina and Grienenberger, 1991;Wintz and Hanson, 1991). Transcripts of many other plant mitochondrial genes are less homogeneous; partially edited transcripts are readily detected and often are more abundant than transcripts that are fully edited (Covello and Gray, 1990;Schuster et al, 1990;Gualberto et al, 1991;Kempken et al, 1991;Salazar et al, 1991;Lu and Hanson, 1992). Such a transcript population has the potential of encoding multiple forms of the gene's protein product.…”