PHYLOGENETIC AFFINITIES OF THE GRASSES TO OTHER MONOCOTS AS REVEALED BY MOLECULAR ANALYSIS OF CHLOROPLAST DNA

The distribution of structural alterations of the chloroplast genome f ound in grass chloroplast (cp) DNA in comparison with that of tobacco was systematically surveyed in the cpDNAs of monocots. Southern hybrid ization and/or PCR analyses for the detection of (1) three inversions in the large single-copy region, (2) loss of an intron in the rpoC1 ge ne, (3) an extra-sequence insertion in the ryoC2 gene, (4) the deletio n of ORF2280, (5) rearrangements of the accD (ORF512) gene, and (6) no n-reciprocal translocation of the rpl23 gene, were carried out on cpDN As isolated from 58 species, 22 families, and 11 orders, which covered almost all families of monocots. These structural alterations of cpDN A mostly occurred at the family level. However, only part of the Resti onaceae possessed the inversion that characterizes the lineage of gras s differentiation. The order of mutational events made it possible to reconstruct grass phylogeny in monocots. Since no variations in struct ural alterations of the cpDNA were found among the Poaceae, grass plan ts were inferred to have originated from an ancestor harboring these s tructural alterations of the chloroplast genome. These phylogenetic re lationships were supported by the sequence data of rbcL.