SEQUENCE-ANALYSIS OF DUPLICATED ACTIN GENES IN LAGENIDIUM-GIGANTEUM AND PYTHIUM-IRREGULARE (OOMYCOTA)

Southern analysis of genomic DNA identified multiple-copy actin gene f amilies in Lagenidium and Pythium irregulare (Oomycota). Polymerase ch ain reaction (PCR) protocols were used to amplify members of these act in gene families. Sequence analysis of genomic coding regions demonstr ated five unique actin sequences in L. giganteum (Lg-Ac1, 2, 3, 4, 5) and four unique actin sequences in P. irregulare (Pi-Ac1, 2, 3, 4); no ne were interrupted by introns. Maximum parsimony analysis of the codi ng regions demonstrated a close phylogenetic relationship between oomy cetes and the chromophyte alga Costaria costata. Three types of actin coding regions were identified in the chromophyte/oomycete lineage. Th e type 1 actin is the single-copy coding region found in C. costata. T he type 2 and type 3 actins are found in the oomycetes and are the res ult of a gene duplication which occurred soon after the divergence of the oomycetes from the chromophyte algae. The type 2 coding regions ar e the single-copy sequence of Phytophthora megasperma, the Phytophthor a infestans actB gene, Lg-Ac5 and Pi-Ac2. The type 3 coding regions ar e the single-copy sequence of Achlya bisexualis, the P. infestans actA gene, Lg-Ac1, 2, 3, 4 and Pi-Ac1, 3, 4.