The Gene Encoding Mitochondrial Succinate Dehydrogenase Subunit 4 Has Been Successfully Transferred to the Nuclear Genome in Pea, while Leaving an Original Sequence as a Pseudogene in the Mitochondrial Genome

Abstract

A sequence homologous to a gene encoding succinate dehydrogenase subunit 4 (sdh4) was found in pea mitochondrial genome but non-functional. A functional sdh4 gene was isolated from pea nuclear genome, suggesting gene transfer from the mitochondrion to the nucleus during evolution. As compared with mitochondrial sdh4 genes, the pea nuclear sdh4 gene has an extension in its N-terminal region, suggesting encoding a protein targeting signal to mitochondria. There are five introns and six exons in the pea nuclear sdh4 gene. Sequence homology to mitochondrial sdh4 is observed in the exon 6 but not in the other five exons, suggesting mitochondrial sequence was integrated downstream of the five exons. Comparison of nuclear sdh4 genomic sequences from pea, Arabidopsis and rice suggests that the number and location of introns are different among the three. Therefore, sdh4 genes may have evolved in the nuclei independently among plant species.