MOLECULAR EVOLUTION OF THE PLANT-R REGULATORY GENE FAMILY

Anthocyanin pigmentation patterns in different plant species are contr olled in part by members of the myc-like R regulatory gene family. We have examined the molecular evolution of this gene family in seven pla nt: species. Three regions of the R protein show sequence conservation between monocot and dicot R genes. These regions encode the basic hel ix-loop-helix domain, as well as conserved N-terminal and C-terminal d omains; mean replacement rates for these conserved regions are 1.02 x 10(-9) nonsynonymous nucleotide substitutions per site per year. More than one-half of the protein, however, is diverging rapidly, with nons ynonymous substitution rates of 4.08 X 10(-9) substitutions per site p er year. Detailed analysis of R homologs within the grasses (Poaceae) confirm that these variable regions are indeed evolving faster than th e flanking conserved domains. Both nucleotide substitutions and small insertion/deletions contribute to the diversification of the variable regions within these regulatory genes. These results demonstrate that large tracts of sequence in these regulatory loci are evolving at a fa irly rapid rate.