Approaches towards disease resistance to filamentous pathogens

In the co-evolutionary arms race between plants and pathogens, plants have developed a multifaceted armory consisting of diverse defence responses, such as the production of antimicrobial compounds and the activation of immunity via specific receptors. This work examines the use of the phytoalexin capsidiol and synthetic NLR immune receptors as disease resistance approaches against oomycete and fungal plant pathogens. The production of phytoalexins constitutes an important aspect of plant defence. Capsidiol, a pepper phytoalexin, differentially inhibits the growth of two Phytophthora species, the late-blight pathogen P. infestans and the vegetable pathogen P. capsici. The differential effect of capsidiol towards these two oomycetes was determined and quantified. I also monitored intraspecific variation among various P. infestans isolates in their sensitivity towards capsidiol. Plant defence machinery also involves intracellular immune receptors of the Nucleotidebinding Leucine-rich Repeat-containing protein family (NLRs). NLRs typically recognize pathogen effector proteins with avirulence activities, leading to a response known as effector-triggered immunity (ETI). R3a and I2 are orthologous NLRs from potato and tomato responding to effectors of P. infestans and the wilt fungus Fusarium oxysporum f. sp. lycopersici, respectively. Yet, particular races of these pathogens have evolved stealthy effectors that evade recognition by R3a and I2. I assessed whether previously identified mutations in R3a, with expanded response specificities to Phytophthora spp. effectors, can be transferred to I2 with similar beneficial effects. I recovered I2 mutants with expanded response spectrum to effectors from both P. infestans and F. oxysporum f. sp. lycopersici. Infection assays in both transient and stable transgenic systems suggested this expanded response correlates with resistance. I finally investigated whether the I2 locus is a determinant of tomato resistance against P. infestans. Overall, these findings generate new insights into the molecular interactions underlying plants response to pathogens, and open up applied perspectives for sustainable crop disease resistance.