RESEARCH ARTICLE

Abstract We used the chloroplast gene rbcL as a model to study the frequency and relative timing of transfer of chloroplast sequences to the mitochondrial genome. Southern blot survey of 20 mitochondrial DNAs con-firmed three previously reported groups of plants con-taining rbcL in their mitochondrion, while PCR studies identified a new mitochondrial rbcL. Published and newly determined mitochondrial and chloroplast rbcL sequences were used to reconstruct rbcL phylogeny. The results imply five or six separate interorganellar transfers of rbcL among the angiosperms examined, and hundreds of successful transfers across all flowering plants. By taxonomic criteria, the crucifer transfer is the most an-cient, two separate transfers within the grass family are of intermediate ancestry, and the morning-glory transfer is most recent. All five mitochondrial copies of rbcL examined exhibit insertion and/or deletion events that disrupt the reading frame (three are grossly truncated); and all are elevated in the proportion of nonsynony-mous substitutions, providing clear evidence that these sequences are pseudogenes. Electronic Supplementary Material is available for this article if you access the article a