Comparison of glyceraldehyde-3-phosphate dehydrogenase genes in Phaeosphaeria nodorum and P. avenaria species

Abstract

Stagonospora leaf blotch of cereals is a complex disease caused by several Phaeosphaeria fungal species. Genetic diversity among glyceraldehydes-3-phosphate dehydrogenase (gpd) genes of Phaeosphaeria nodorum, P. avenaria f. sp. triticea (P.a.t.) and P. avenaria f. sp. avenaria (P.a.a.), three causal agents of stagonospora leaf blotch diseases in cereals, was evaluated in this study. The PCR-amplified gpd gene from these cereal Phaeosphaeria species contained 4 introns. The gpd gene in wheat-biotype P. nodorum isolates ranged in size from 1,253-1,255bp. Sequence variations in intron 4 were used to divide the wheat-biotype P. nodorum isolates into two subgroups. These two subgroups were equally represented in a survey of field wheat-biotype P. nodorum isolates. Except Pat2, the gpd genes in Patl and Pat3 of the P.a.t. group, the P.a.a. group and the barley-biotype P. nodorum were 1,251 bp in length and phylogenetically closely related. As the nucleotide changes in gpd genes occurred mostly in intron regions and the third codons of amino acid coding triplets, the deduced protein sequences in three cereal Phaeosphaeria species were identical, except for Pat2. The gpd-encoded protein in Pat2 isolates contained two amino acid substitutions. The deduced GPD proteins of three cereal Phaeosphaeria species are closely related to the GPD protein that has been described in a maize pathogen, Cochliobolus heterostrophus. Based on phylogenetic analysis, the possible evolution of these cereal Phaeosphaeria species in relation to other ascomycetes is discussed.