Stagonospora nodorum Berk. is the causal agent of Septoria nodorum blotch (SNB) of wheat (Triticum aestivum L.). It synthesizes host-specific necrotrophic effectors (NEs), which facilitate infection process and ensure virulence of pathogen on host plant with a dominant susceptibility gene. The interaction of virulence genes products of the NEs pathogen (SnTox) with susceptibility genes products of the host plant (Snn) in the S. nodorum - wheat pathosystem is carried out in inverted gene-for-gene system and causes the development of disease. In this study, we tested three main NEs SnToxA, SnTox1, SnTox3, which have already been identified in S. nodorum at the gene level. The NEs role in the development of SNB has already been proven; however, the overall host response to SNB does not always strictly follow the inverted gene-for-gene system, as multiple SnTox-Snn interactions can be additive or epistatic. In this regard, the aim of the work was to identify the NE genes in three S. nodorum isolates and to study effect of NEs genes transcriptional activity on the isolate virulence. We have shown that all three NEs SnToxA, SnTox3 and SnTox1 played an important role in the development of the disease in compatible interactions. Effectors SnTox3 and SnTox1 exhibited epistatic interaction that was removed by a triple compatible interaction (SnTox3-Snn3, SnToxA-Tsn1 and SnTox1-Snn1). This effect was shown by us for the first time. The mechanisms of epistatic and additive interactions, as well as the virulence of the isolate were associated with the regulation of the NEs genes transcriptional activity. The avirulent isolate Sn4VD lacked transcription of all three NEs genes, and the virulent isolate Sn9MH was characterized by a high level of mRNA accumulation of all three NEs genes during infection on susceptible cultivar. We also showed that SnTox expression depended both on the host genotype in SnToxA and SnTox3 and on the number of compatible interactions exhibiting additive or epistatic interactions in SnTox1 and SnTox3. Finally, the virulence of the S. nodorum isolate depended on the qualitative and quantitative composition of NEs.
Role of the Stagonospora nodorum effector SnTox3 in regulation of cytokinins synthesis and metabolism in infected wheat plants
