Interorganellar DNA transfer in wheat: dynamics and phylogenetic origin.
Bottom Line: Six other xenologs showed recurrent transfer from the ct to mt genomes in more than one taxon.The two remaining xenologs were uninformative on the evolutionary timing of their transfer.The wheat mt nad9 gene was found to be chimeric, consisting of the cereal nad9 gene and its 291 bp 5'-flanking region that included a 58 bp xenolog of the ct-ndhC origin.
Affiliation: Kyoto University, Japan. email@example.com
A homology search of wheat chloroplast (ct) and mitochondrial (mt) genomes identified 54 ctDNA segments that have homology with 66 mtDNA segments. The mtDNA segments were classified according to their origin: orthologs (prokaryotic origin), xenologs (interorganellar DNA transfer origin) and paralogs (intraorganellar DNA amplification origin). The 66 mtDNA sequences with homology to ctDNA segments included 14 paralogs, 18 orthologs and 34 xenologs. Analysis of the xenologs indicated that the DNA transfer occurred unidirectionally from the ct genome to the mt genome. The evolutionary timing of each interorganellar DNA transfer that generated a xenolog was estimated. This analysis showed that 2 xenologs originated early in green plant evolution, 4 in angiosperm evolution, 3 in monocotyledon evolution, 9 during cereal diversification and 8 in the evolution of wheat. Six other xenologs showed recurrent transfer from the ct to mt genomes in more than one taxon. The two remaining xenologs were uninformative on the evolutionary timing of their transfer. The wheat mt nad9 gene was found to be chimeric, consisting of the cereal nad9 gene and its 291 bp 5'-flanking region that included a 58 bp xenolog of the ct-ndhC origin.
Mentions: The xenology of the no. 22 mtDNA segment to its counterpart ctDNA segment needs special mention because they carried partial sequences of the active mt-nad9 and ct-ndhC genes, respectively; both genes encode an NADH dehydrogenase subunit. Neither of the two prokaryote genomes had sequences with significant homology to the no. 22 segment, indicating the non-orthologous origin of these segments in the mt and ct genomes. Homologues of the no. 22 mtDNA segment were found only in the monocotyledon species (ref. Table 6), whereas nad9 and ndhC were found, respectively, in the mt and ct genomes of all green plants (Fig. 2).