XVI International Botanical Congess

Plastid rpo genes encode the subunits of a eubacterial-type, multi-subunit RNA polymerase. In plants of the genus Pelargonium (Rosidae: Geraniaceae), the rpo genes are evolving at a highly accelerated rate. Moreover, this evolutionary acceleration is found primarily at nucleotide sites which change the encoded amino acid, suggesting the presence of a selective force favoring amino acid sequence divergence. This evidence of positive Darwinian selection in favor of divergence, together with the magnitude of change, raises numerous questions about the effects of the accelerated evolution on the function of the polymerase. We report here the development of a novel non-radioactive assay for activity of multi-subunit RNA polymerases and its use in the purification of functional RNA polymerase from angiosperm chloroplasts.