Mitochondrial genome conformation and cytochrome respiration-related functions among the CW-group chlorophycean algae.

摘要

Available data suggest that among green algae (Chlorophyta, sensu Sluiman 1985) most taxa have circular-mapping mitochondrial genomes with other taxa having linear genome- or subgenomic-sized mitochondrial DNAs (mtDNA). To date, all examples of the linear mtDNA forms are confined to the Volvox-clade (sensu Nakayama et al. 1986) of the chlorophycean CW (basal bodies displaced clockwise)-group, although there is no information regarding the conformation of mtDNA from taxa of the Oogamochlamys-clade (sensu Proschold et al. 2001), which may be the extant clade most closely related to the Volvox-clade. It is not clear, however, if the circular-mapping genomes represent genome-sized circular molecules, if such circular molecules and the linear forms are the predominant in vivo mtDNA structures, nor if the linear forms arose only once or multiple times among extant green algal lineages. It was thus of interest to examine the DNA components detected with homologous mtDNA probes following pulsed field gel electrophoresis of total cellular DNA from the chlorophycean CW-group green algal taxa Chlamydomonas reinhardtii and Chlamydomonas moewusii. The 15.8-kb linear mtDNA of C. reinhardtii was the only DNA component detected, and there was no evidence of circular or large linear mtDNA precursors of this 15.8-kb linear form. For C. moewusii, which has a circular-mapping 22.9-kb mitochondrial genome, total cellular DNA revealed a mixture of DNA components that hybridized to the mtDNA probe. In further studies, the mitochondrial genome conformation of additional CW-group taxa was examined using conventional gel electrophoresis and Southern blot analysis with mtDNA probes. The results of these experiments indicate that all taxa from the Volvox-clade have genome- or subgenomic-sized linear mtDNAs as their predominant mtDNA form. (Abstract shortened by UMI.)