Molecular phylogeny of Flaveria as deduced from the analysis of nucleotide sequences encoding the H-protein of the glycine cleavage system

Sequence comparisons have shown that nucleotide sequences of the H-protein, a component of the glycine cleavage system, are only moderately conserved and can be used as molecular maskers for intrageneric phylogenetic studies. We have analysed the respective cDNA sequences from 12 species of Flaveria, and a more limited set of gdcsH upstream regions. These data are discussed with respect to a phylogenetic reconstruction of Flaveria, a small genus which includes species of different photosynthetic types, namely C-3, C-3-C-4, C-4-like and C-4. Our analysis essentially supports an earlier hypothesis, based an morphological and eco-geographical data, of the evolution of Flaveria (Powell 1978). This close agreement shows the usefulness of H-protein nucleotide sequences at a low taxonomic level. Our analysis independently confirms that C-4 photosynthesis has evolved two times in different lineages of Flaveria. Most remarkably, the C-4 taxa of Flaveria appear as derived relative to the C-3-C-4 intermediate taxa, i.e. they probably have common direct predecessors. This is the first direct evidence for a phylogenetically intermediate position of C-3-C-4 intermediate photosynthesis. Our data also confirm the antiquity of Ca photosynthesis in Flaveria but suggest that the collection of F. pringlei used in our experiments, although clearly of C, photosynthetic metabolism, possibly originated from hybridization with a more advanced taxon.