EVOLUTION OF ALCOHOL-DEHYDROGENASE GENES IN PEONIES (PAEONIA) - PHYLOGENETIC-RELATIONSHIPS OF PUTATIVE NONHYBRID SPECIES

Alcohol dehydrogenase genes were amplified by PCR, cloned, and sequenc ed from 11 putative nonhybrid species of the angiosperm genus Paeonia. Sequences of five exons and six intron regions of the Adh gene were u sed to reconstruct the phylogeny of these species. Two paralogous gene s, Adh1A and Adh2, were found; an additional gene, Adh1B, is also pres ent in section Moutan. Phylogenetic analyses of exon sequences of the Adh genes of Paeonia and a variety of other angiosperms imply that dup lication of Adh1 and Adh2 occurred prior to the divergence of Paeonia species and was followed by a duplication resulting in Adh1A and Adh1B . Concerted evolution appears to be absent between these paralogous lo ci. Phylogenetic analysis of only the Paeonia Adh exon sequences, posi tioning the root of the tree between the paralogous genes Adh1 and Adh 2, suggests that the first evolutionary split within the genus occurre d between the shrubby section Moutan and the other two herbaceous sect ions Oneapia and Paeonia. Restriction of Adh1B genes to section Moutan may have resulted from deletion of Adh1B from the common ancestor of sections Oneapia and Paeonia. A relative-rate test was designed to com pare rates of molecular change among lineages based on the divergence of paralogous genes, and the results indicate a slower rate of evoluti on within the shrubby section Moutan than in section Oneapia. This may be responsible for the relatively long branch length of section Oneap ia and the short branch length between section Moutan and the other tw o sections found on the Adh, ITS (nrDNA), and matK (cpDNA) phylogenies of the genus. Adh1 and Adh2 intron sequences cannot be aligned, and w e therefore carried out separate analyses of Adh1A and Adh2 genes usin g exon and intron sequences together. The Templeton test suggested tha t there is not significant incongruence among Adh1A, ITS, and matK dat a sets, but that these three data sets conflict significantly with Adh 2 sequence data. A combined analysis of Adh1A ITS, and matK sequences produced a tree that is better resolved than that of any individual ge ne, and congruent with morphology and the results of artificial hybrid ization. It is therefore considered to be the current best estimate of the species phylogeny. Paraphyly of section Paeonia in the Adh2 gene tree may be caused by longer coalescence times and random sorting of a ncestral alleles.