STRUCTURE AND EVOLUTION OF THE ACTIN GENE FAMILY IN ARABIDOPSIS-THALIANA

Higher plants contain families of actin-encoding genes that are diverg ent and differentially expressed. Progress in understanding the functi ons and evolution of plant actins has been hindered by the large size of the actin gene families. In this study, we characterized the struct ure and evolution of the actin gene family in Arabidopsis thaliana. DN A blot analyses with gene-specific probes suggested that all 10 of the Arabidopsis actin gene family members have been isolated and establis hed that Arabidopsis has a much simpler actin gene family than other p lants that have been examined. Phylogenetic analyses suggested that th e Arabidopsis gene family contains at least two ancient classes of gen es that diverged early in land plant evolution and may have separated vegetative from reproductive actins. Subsequent divergence produced a total of six distinct subclasses of actin, and five showed a distinct pattern of tissue specific expression. The concordance of expression p atterns with the phylogenetic structure is discussed. These subclasses appear to be evolving independently, as no evidence of gene conversio n was found. The Arabidopsis actin proteins have an unusually large nu mber of nonconservative amino acid substitutions, which mapped to the surface of the actin molecule, and should effect protein-protein inter actions.