The Arabidopsis thaliana PSS1 Gene Confers Nonhost Resistance Against Two Soybean Pathogens, Phytophthora sojae and Fusarium virguliforme

The mechanisms that confer wide-spectrum protection in a plant species against all isolates of a pathogen are termed as nonhost resistance. Arabidopsis confers nonhost resistance against most soybean pathogens including the Asian soybean rust fungus and hemi-biotrophic pathogen Phytophthora sojae that causes root and stem rot disease. Three Arabidopsis genes, PEN1, 2 and 3 were recently shown to be involved in the expression of Arabidopsis pre-haustorial nonhost resistance against a powdery mildew pathogen. Arabidopsis pen1-1 mutant is penetrated by P. sojae. Over 3,000 M₂ families were created by treating pen1-1 with EMS and screened for mutants that showed loss of resistance against P. sojae and identified a Phytophthora sojae susceptible mutant, pss1. Genetic data suggest that PEN1 is not epistatic to PSS1. PSS1 was mapped to a region very close to the southern telomere of chromosome 3. We challenged six P. sojae susceptible and six resistant families, generated from a cross segregating for the alleles at the PSS1 locus with the fungal pathogen, Fusarium virguliforme that causes sudden death syndrome in soybean. We observed that PSS1 is required for Arabidopsis nonhost resistance against F. virguliforme. Thus, PSS1 governs a novel nonhost defense mechanism against two highly destructive soybean pathogens.