Extensive and widespread homologies between mitochondrial DNA and chloroplast DNA in plants

Abstract

Hybridization techniques were used to demonstrate that numerous sequence homologies exist between cloned mung bean [Vigna radiata] and spinach [Spinacia oleracea] chloroplast DNA (ctDNA) restriction fragments and mtDNA from corn [Zea mays], mung bean, spinach and pea [Pisum sativum]. The strongest cross-homologies are between clones derived from the ctDNA inverted repeat and mtDNA from corn and pea, although all the ctDNA clones tested hybridized to at least 1 mtDNA restriction fragment. Known chloroplast genes showing strong mtDNA homologies include those for the large subunit of ribulosebisphosphate carboxylase, which hybridizes to corn mtDNA, and the .beta. subunit of the chloroplast ATPase, which hybridizes to mung bean mtDNA. Certain of these homologies were confirmed by using cloned spinach mtDNA restriction fragments as probes in reciprocal hybridizations to ctDNA. Several of these ctDNA-homologous mtDNA sequences were much more closely related to ctDNA from the same species than to that of a distantly related species. These differential homologies are evidence for relatively recent DNA sequence transfer events, suggesting that transposition between the 2 genomes is an ongoing evolutionary process.