Submitted to: Canadian Journal of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/20/2005
Publication Date: 9/22/2005
Citation: Reszka, E., Chung, K.R., Tekauz, A., Malkus, A., Arseniuk, E., Krupinsky, J.M., Ueng, P.P. 2005. Presence of b-glucosidase (bg11) gene in phaeosphaeria nodorum and p. avenaria f. sp. triticea. Canadian Journal of Botany. 83:1001-1014. Interpretive Summary: Stagonospora leaf blotch disease of oat caused by the fungal pathogen, Phaeosphaeria avenaria f. sp. avenaria, is important worldwide. The pathogen produces a specific ß-glucosidase enzyme to destroy toxic secondary metabolites (saponins) in oat leaves to facilitate fungal infection, and thus, plays a role in disease development. In this study, we discovered that other important cereal Phaeosphaeria pathogens possess a similar enzyme. Genetic variation of the gene encoding ß-glucosidase can be used to study the evolution and molecular identification of this group of fungi. We also discovered that the conventional classification of Phaeosphaeria avenaria based on host specificity in cereals may be inaccurate. The results will be of interest to scientists and diagnostics latoratories for molecular classification and identification of cereal fungal pathogens.
Technical Abstract: Phaeosphaeria avenaria f. sp. avenaria (Paa), the causal agent of Stagonospora leaf blotch in oats, produces a glycosyl hydrolase family 3 enzyme, ß-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 similar ß-glucosidase gene (bgl1) was PCR-amplified from two cereal Phaeosphaeria species, P. nodorum and P. avenaria f. sp. triticea, a Phaeosphaeria isolate S-93-48 from dallis grass (Paspalum dilatatum Poir.) and a P. nodorum isolate Sn48-1 from rye (Secale cereale L.). Different sizes of bgl1 gene coding sequences ranging from 3018-3023bp were determined. The bgl1 gene structure in these Phaeosphaeria species was identical to Paa, and contained 4 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 12bp 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 two P. avenaria f. sp. triticea isolates ATCC26370 and ATCC26377 (Pat2) from foxtail barley (Hordeum jubatum L.) and some homothalic P. avenaria f. sp. triticea isolates (Pat1). With sequence similarities in the noncoding internal transcribed spacer (ITS) region of nuclear rDNA, the partial gpd gene fragment containing the intron 4, and the full-length bgl1 gene, 5 Phaeosphaeria isolates (5413, 1919WRS, 1920WRS, 1921WRS, Sa37-2) from oat (Avena sativa L.) 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.