Mitochondrial gene expression in Cucurbitaceae: conserved and variable features.

We have examined mitochondrial DNA (mtDNA) sequence conservation, transcriptional patterns of mitochondrial genes, and mitochondrial translation products in four species of the plant family Cucurbitaceae, in which there is a seven-fold range in mitochondrial genome size. A set of conserved mtDNA sequences which we term "core" DNA is present in all cucurbit genomes examined. In watermelon, only those mtDNA restriction fragments which contain "core" DNA hybridize with mtRNA. Similar numbers of polypeptides are synthesized by isolated mitochondria from all species examined, but an extra set of mtDNA sequences is transcribed in the largest genome (muskmelon). Taken together, these results suggest that some mtRNA is untranslated in muskmelon. Cloned mitochondrial genes of known function, from maize, identified mitochondrial transcripts that varied in both size and number among cucurbit species.