The evolution of angiosperm actin genes.

Abstract

Forty-four actin genes from five angiosperm species, whose evolutionary relationships are well characterized, were PCR-cloned and sequenced. Phylogenetic analysis of 34 of these actin genes, along with those previously published, indicate that plant actin genes are monophyletic and underwent a rapid radiation early in land plant evolution. Six sets of putative orthologues have been identified and their sequences were used to calculate rates of evolution. The synonomous rate of substitution $(5.44\times10\sp{-9}$/site/year) is similar to that of other nuclear protein-encoding genes but the non-synonomous rate $(0.13\times10\sp{-9}$/site/year) is 4-10 times higher than that of vertebrate actin genes. Relative-rate tests do not support a faster rate in plants than in vertebrates. Evidence is also provided that some members of the actin multigene family in maize are undergoing gene conversion. Finally, we show that some plant actin genes have undergone intron loss probably as a consequence of a gene conversion event between the genomic copy and the reverse transcript.