Expression profile of defense-related genes in susceptible and resistant wheat cultivars in response to powdery mildew infection

Bread Wheat is one of the most important crops which has main position in nutrition of the world''s population. Powdery mildew، caused by the biotrophic pathogen Blumeria graminis f. sp tritici (Bgt)، is one of the most destructive diseases of wheat worldwide. Plants in response to biological agents produce numerous compounds such as reactive oxygen species، phytoalexins and a group of proteins called pathogenesis related (PR) proteins. In this research the expression rate of PAL and some PR genes including PR1، PR2، and PR3 were evaluated using quantitative PCR (qPCR) technique in two resistance and susceptible genotypes in response to Bgt. Primarily، 40 commercial Iranian wheat genotypes were screened with Bgt in seedling stage. On the basis of colonies number formed on samples، Tajan and Flat were selected as resistance and susceptible lines، respectively. To show the role of mentioned genes in powdery mildew disease resistance، these selected lines were inoculated to Bgt and sampling was carried out at 5 time courses. The experiment was performed in 3 independent replicate and the genes expression rate were normalized، in comparing with their relative internal reference gene، actin. Comparisons of genes expression patterns showed that the expression levels of all target genes was increased in both resistant and susceptible cultivars after infection with powdery mildew agent. Investigation of gene expression process showed that the expression level of all target genes in Tajan cultivar increased faster than Falat cv. In both cultivars، the maximum expression level of genes were observed at 24 h after infection to prevent the establishment of hastorium in host cells by Bgt. Maximum expression level of all genes in Tajan resistance cultivar were much higher than Falat susceptible cv. Results of this study direct that these evaluated genes are involved in resistance strategy beside the other major genes. In resistance and susceptible cultivars their transcript levels attenuated at 48 h، but this level in Falat cv. was lower than Tajan cv، consistently. As well، the PR1 transcript levels was major than the other genes. In peak time point the PR1 transcript levels in Tajan resistance cv was 2. 2 fold more than Falat susceptible cultivar. This finding demonstrate that PR1 genes has crucial role in wheat powdery mildew resistance.