Presence of β-glucosidase (bgl1) gene in Phaeosphaeria nodorum and Phaeosphaeria avenaria f.sp. triticea

Abstract

Phaeosphaeria avenaria f.sp. avenaria (Paa), the causal agent of stagonospora leaf blotch in oats, produces a glycosyl hydrolase family 3 enzyme, β-glucosidase, which is responsible for detoxification of steroidal avenacosides in oat leaves, but is not essential for pathogenicity. For a comparative genetic relatedness study, a Paa-like β-glucosidase gene (bgl1) was PCR-amplified from Phaeosphaeria nodorum and P. avenaria f.sp. triticea, and Phaeosphaeria spp. from dallis grass (Paspalum dilatatum) (isolate S-93-48) and rye (Secale cereale) (isolate Sn48-1). Different sizes of bgl1 gene coding sequences ranging from 3018 to 3023 bp were determined. The bgl1 gene structure in these Phaeosphaeria species was identical to that of Paa and contained four exons and three introns. Nucleotide variations occurring in introns 1 and 2 of the bgl1 gene divided wheat-biotype P. nodorum into four groups. Two 12-bp-long direct sequence repeats (5'-TCA/G ACT GGT TT/CA/G) were found in the promoter region of the bgl1 gene in Phaeosphaeria species; only one repeat was present in the two P. avenaria f.sp. triticea isolates ATCC26370 and ATCC26377 (Pat2) from foxtail barley (Hordeum jubatum) and some homothallic P. avenaria f.sp. triticea isolates (Pat1). With sequence similarities in the noncoding internal transcribed spacer region of nuclear rDNA, the partial gpd gene fragment containing the intron 4, and the full-length bgl1 gene, five Phaeosphaeria isolates (5413, 1919WRS, 1920WRS, 1921WRS, Sa37-2) from oat (Avena sativa) were molecularly determined to be Paa. Two oat isolates (Sa38-1 and Sa39-2) from Poland appeared to be Pat1. The results suggest that classification of two Phaeosphaeria avenaria formae speciales based on host specificity should be re-evaluated.Key words: wheat, oat, Phaeosphaeria, β-glucosidase gene.