EDS1-mediated basal defense and SA-signaling contribute to post-invasion resistance against tobacco powdery mildew in Arabidopsis

Arabidopsis-powdery mildew is a unique pathosystem in dissecting the molecular mechanism of plantbiotrophic fungus interactions. To increase the diversity of powdery mildew pathogens, we identified a tobacco powdery mildew, designated Gc SICAU1, which belonged to Golovinomyces cichoracearum (Gc) based on the internal transcribed spacer (ITS) rDNA fragment sequences. Inoculation test in laboratory conditions revealed that Gc SICAU1 could colonize on wild type Arabidopsis Col-O leaves, but failed to grow as abundantly on tobacco leaves, indicating that Gc SICAU1 has completely overcome the pre-invasion resistance and its colonization is hindered by the post-invasion resistance in Arabidopsis. The growth of Gc SICAU1 in the fls2, efr-1 and pen1-1 mutants displayed no obvious difference from that of wild type plants. In contrast, salicylic acid (SA)-signaling deficient mutants such as pad4-1 and eds5-1, but not ethylene-signaling mutants, exhibited increased susceptibility to Gc SICAU1. Moreover, eds1-2 and pad4-1/sid2-1 were fully susceptible to Gc SICAU1 and the disease symptom was comparable to Gc SICAU1 on tobacco leaves. These data indicate that EDS1-mediated basal defense and SA-signaling play critical roles for post-invasion resistance against this pathogen. Taken together, our data demonstrated that Gc SICAU1 is a pathogen weakly virulent to Arabidopsis and can be used as a tool to finely dissect post-invasion resistance mechanisms. (C) 2015 Elsevier Ltd. All rights reserved.