IDENTIFICATION AND CHARACTERIZATION OF NOVEL PLANT IMMUNE COMPONENTS USING THE ARABIDOPSIS-POWDERY MILDEW PATHOSYSTEM
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Despite tremendous progress in the field of plant immunity in the past two decades, how plants mount spatiotemporally appropriate defenses against pathogens is still not well characterized. My thesis project took both forward and reverse genetic approaches to uncover novel mechanisms used by plants to fight against fungal pathogens, or exploited by fungi to adapt to host plants using the Arabidopsis-powdery mildew pathosystem. Through a reverse genetics approach, I found that two phospholipase D (PLD) genes PLDα1 and PLDδ play opposing roles in modulating basal, post-penetration resistance against mildew through a novel, yet-to-be characterized mechanism that is independent of EDS1/PAD4 (key immune components), salicylic acid (SA), and jasmonic acid (JA). Inspired by this finding, I designed and performed a large-scale forward genetic screen in the background of a super-susceptible Arabidopsis eds1-2pad4-1sid2-2 (eps) triple mutant. By screening EMS-mutagenized eps plants using powdery mildew species with different levels of adaptation on Arabidopsis, 5 susceptible to non-adapted PM (snap) and 18 compromised immunity yet poor infection (cipi) mutants have been identified. So far, this has led to the characterization of the MAP KINASE PHOSPHATASE1 (MKP1) gene, which is a negative regulator of PAMP-triggered immunity, and the MILDEW RESISTANCE LOCUS 2 (MLO2) gene, a susceptibility factor of powdery mildew, both of which act independently of EDS1, PAD4, and SA. Together, results from this work should contribute to a better understanding of the multi-layered plant immune system and powdery mildew’s host adaptation mechanisms.