A complex gene superfamily encodes actin in petunia.

We have shown by several independent criteria that actin is encoded by a very large and complex superfamily of genes in Petunia. Several cDNA and genomic probes encoding actins from diverse organisms (Dictyostelium, Drosophila, chicken and soybean) hybridize to hundreds of restriction fragments in the petunia genome. Actin-hybridizing sequences were isolated from a petunia genomic library at a rate of at least 200 per genome equivalent. Twenty randomly selected actin-hybridizing clones were characterized in more detail. DNA sequence data from four representative and highly divergent clones, PAc2, PAc3, PAc4 and PAc7, demonstrate that these actin-like sequences are related to functional actin genes. Intron positions typical of other known plant actin genes are conserved in these clones. Four of six clones analyzed (PAc1, PAc2, PAc3, PAc4) hybridize to leaf mRNA of the same size (1.7 kb) as that reported for other plant actin mRNAs and to a slightly smaller mRNA species (1.5 kb). Five distinct subfamilies of actin-related genes were characterized which varied in size from a few members to several dozen members. It is clear from our data that other actin gene subfamilies must also exist within the genome. Possible mechanisms of actin gene amplification and genome turnover are discussed.