P-356 - Chasing the molecular basis of the pleiotropic phenotypes in powdery mildew-resistant A. thaliana mlo mutants

Obligate biotrophic fungi of the Erysiphaceae family pose an omnipresent threat to agriculture as they cause powdery mildew diseases. Mutants defective in isoforms of Mildew resistance locus o (Mlo) are highly immune to infections with powdery mildew fungi. In Arabidopsis thaliana, this reduced susceptibility is accompanied by developmentally controlled pleiotropic phenotypes that are reminiscent of the premature leaf senescence. Previous studies suggested a link between the AtMLO2 protein and a downstream signaling pathway induced by an unknown nucleotide-binding domain leucine-rich repeat (NLR) immune receptor causing these pleiotropic phenotypes. We aimed to substantiate this proposed link by investigating the impact of mutations of the immune signaling components EDS1, PAD4, SAG101, ADR1, NRG, RPW8 and NDR1 in the background of mlo2. Therefore, I characterized the susceptibility of the different genotypes to powdery mildew, checked the development of callose deposits and analyzed the correlation between the premature senescence phenotype and salicylic acid concentrations. The results indicate a requirement of the EDS1-PAD4-ADR1 module for the formation of pleiotropic effects in mlo2 plants. By identifying these components, I was able to narrow down the involved immune pathway and thus the corresponding NLR likely to the TNL (TIR-NLR) family. The next step is to identify promising TNL candidates that could be involved in the regulation of the mlo2 pleiotropic phenotypes.