Complex II subunit 4 (sdh4) homologous sequences in plant mitochondrial genomes

Through cDNA analysis a 95-codons-long novel open reading frame (orf) is identified in the Arabidopsis thaliana mitochondrial genome, overlapping the 3' end region of the cox3 gene. This sequence is conserved in other dicot plants such as Oenothera, pea and sunflower, but is not detected in wheat mitochondrial DNA. The Apabidopsis, sunflower and Oenothera sequences may be pseudogenes, with the first two being shortened by stop codons and transcription of the latter terminating within the orf. However, RNA editing increases the similarity to homologous Marchantia, algal and bacterial polypeptides, suggesting that this orf could code for the complex-II membrane-anchor subunit (SDH4) in at least some higher-plant species.