Transcriptome Analysis of the Wheat/Wheat Powdery Mildew Interaction

Blumeria graminis f. sp. tritici is a pathogen causing powdery mildew of wheat. It is an obligate biotrophic fungus with high host specificity. In this interaction, effectors are believed to play an important role in suppressing wheat immunity and facilitating host reprogramming for nutrient uptake. It is proposed that the genetic background, effector content, and transcriptional programs together play a role in tuning the virulence of the pathogen.

In this work, the nature and level of changes in gene expression upon wheat infection with three powdery mildew isolates are studied. An RNAseq approach was used to study the compatible interaction during formation of “haustorium”: a feeding structure mediating successful pathogen infection and disease progression. Sequencing data were generated from (i) uninfected wheat leaves, and (ii) wheat leaves infected with the mildew isolates 96224, JIW2 and 94202. On the pathogen side, we found significant differences between isolates in the nature and level of expression of effector genes suggesting isolate specific regulatory programs. Effectors are statistically overrepresented in highly expressed genes suggesting that the fungus is investing massively in their expression at this stage of the infection. They are also statistically overrepresented among the most differentially expressed genes between isolates. We propose that these differences between isolates could be associated to the fitness of the pathogen or to race specificity. Finally, we found that most of the differences are due to a few effector gene families suggesting that these families are more important for virulence at this stage than others. Based on this observation, we hypothesize that different effectors families distinctly contribute to different phases of disease development.