Professor University of Maryland College Park Rockville, Maryland
Body of Abstract: Plant non-host resistance (NHR) is a phenomenon in which all genotypes of a plant species are immune to all strains of a phytopathogen species. In most cases where a non-adapted filamentous pathogen attacks a potential host plant, the genetic and molecular basis of NHR remains poorly characterized mainly because the NHR may consists of multiple layers that often lacks intraspecific variation. To circumvent these inherent barriers, an Arabidopsis triple mutant eds1pad4sid2 (eps) severely compromised in post-penetration resistance was subjected to saturated mutagenesis and genetic screens for mutants susceptible to non-adapted strawberry powdery mildew (snap) that is arrested by penetration resistance. By deploying this “bottom-up” forward genetics strategy, more than 100 snap mutants were isolated. Genetic mapping and cloning has identified causal mutations in PEN2, PEN3,PEN4 and five other genes such as PKL and VIP6 previously unknown to be required for penetration resistance. Next, an Arabidopsis quintuple mutant, eds1pad4sid2pen1pen2 (epsp1p2) was made and subjected to a stepwise forward genetic screens for mutants susceptible to non-adapted barley powdery mildew Bgh (snab). Among a dozen of snab mutants isolated, snab1 contains a causal mutation in AMSH1, a gene encoding a deubiquitinase that interacts with the ESCRT machinery. CRISPR-targeted mutagenesis of additional six immunity genes in the background of eds1pad4sid2pen1pen2pen3amsh1 led to almost a complete breakdown of NHR to non-adapted powdery mildew species. Altogether, our results not only demonstrate that NHR against filamentous fungi is breakable but also provide fresh insight into regulatory mechanisms of plant immunity.