The fungus Parastagonospora nodorum, the causal agent of septoria nodorum blotch (SNB), is responsible for substantial economic losses of wheat worldwide. P. nodorum has emerged as a model organism for studying the pathogenesis of necrotrophic pathogens due to the secretion of multiple proteinaceous necrotrophic effectors (NEs) that induce compatible interactions with hosts possessing corresponding dominant susceptibility (S) genes. Iran is located in the Fertile Crescent considered as a center of origin for P. nodorum, however to date our knowledge on the phenotypic and molecular basis of wheat-P. nodorum interactions in this region remains limited. The understanding of plant-pathogen interaction is essential to develop new disease control strategies. Transcription factors (TFs) are one of the most important regulators of the gene expression. Despite the presence of a high number of TF-encoding genes within the genome of P. nodorum, very little is known about their expression profiles and their functions. This study focused on unraveling the virulence pattern of Iranian isolates of P. nodorum on a diverse panel of wheat genotypes and to analyze the preva‎lence of NE genes SnToxA, SnTox1, SnTox3, and SnTox5, and the corresponding S genes Tsn1, Snn1, and Snn3 in P. nodorum isolates and wheat genotypes, respectively. Besides, the expression profile and functional analysis of ten candidate TF genes were assessed in this study. To do so, the pathogenicity assay of 32 Iranian isolates of P. nodorum collected from the main wheat growing regions in Iran plus reference isolate SN15 was conducted on 19 popular Iranian cultivars, 16 world wheat genotypes, and a set of five SNB differential lines under a factorial randomized complete block design. Disease severity (DS) was scored based on the percentage of leaf area covered with lesions. A multiplex PCR was developed to detect NE and S genes. Based on the results, there was a significant difference among isolates of P. nodorum in virulence against wheat genotypes. Wheat genotypes were classified into six groups highly resistant, resistant, moderately resistant, moderately susceptible, susceptible, and highly susceptible based on their variable responses to P. nodorum isolates. A correlation between disease severity and presence/absence of S genes was observed in this study. Wheat cultivars possessing all three S genes were categorized as highly susceptible, susceptible, and moderately susceptible. The S gene Tsn1 was present in 70 % of the highly susceptible cultivars and completely absent in all resistant cultivars. Furthermore, infiltration of SnToxA resulted in necrosis response exclusively in wheat genotypes harboring the S gene Tsn1. The expression profiles of ten candidate TF genes in P. nodorum including four of which shared homology with well-known fungal TFs, and the other six genes located in the secondary metabolite biosynthetic gene clusters were investigated using quantitative RT-PCR assay under in vitro and in planta conditions. The results revealed that six candidate TF genes exhibited the highest expression levels in the minimal media lacking both nitrogen and carbon sources as well as during the early stages of infection suggesting that candidate TFs may play an important role in the pathogenicity of P. nodorum. To assess the role of candidate TF genes, the TF gene deletion construct was generated using multisite GatewayTM cloning strategy replacing the TF gene with the hygromycin phosphotransferase (hph) gene as a selection marker. The comparison of mutants and WT showed that the candidate TFs play an important role in the mycelial growth, sporulation, oxidative stress tolerance response, and virulence in P. nodorum. Overall, these findings extend our substantial knowledge of P. nodorum-wheat interactions and their underlying molecular basis in Iran, a country in the Fertile Crescent where both wheat and its pathogens coevolved.

بهرام شريف نبي , رحيم مهرابي

امير مساح

مسعود بهار , اقافخر ميرلوحي فلاورجاني , محمد جوان نيكخواه