Modulation of the Effector-Triggered Immunity response by ERAD-Mediated Degradation of Activated NLRs (EMDAN)

A plant disease resistance response can be triggered by the interaction of nucleotide binding leucine-rich repeat proteins (known as resistance proteins) and specific pathogen-derived proteins known as effectors. This interaction leads to a strong defense response known as effector-triggered immunity (ETI), often resulting in a rapid localized cell death response at the site of pathogen infection. This response must be tightly regulated so it confers resistance, but not excessive so that it inhibits plant growth unnecessarily. Our preliminary evidence suggests that a component of a common protein degradation pathway in maize, ZmCER9, controls degradation of the nucleotide binding leucine-rich repeat proteins, after they are activated. ZmCER9 protein sequence is similar to other proteins involved in a process called endoplasmic reticulum associated degradation (ERAD), which degrades incorrectly-folded proteins. Although ERAD has been characterized in yeast, it is poorly understood in plants. Thus, the interaction of ZmCER9 and subsequent degradation of nucleotide binding leucine-rich repeat proteins appears to be a previously undescribed mechanism that mediates the deactivation of the effector-triggered immunity defense response after activation. We will use a range of techniques to gain insight into how the interaction of CER9 homologs and nucleotide binding leucine-rich repeat proteins control a crucial defense response in plants and identify other proteins involved in this process in plants. This study will contribute to a greater understanding of how plants survive and thrive in the face of biotic stress. This project will also provide training opportunities and STEM enrichment to underserved middle and high school students from low income, rural counties in northeastern, helping to generate the next generation of plant scientists.Plant disease resistance (R-) proteins of the nucleotide binding leucine-rich repeat (NLR) type are activated and induce a strong defense response known as effector-triggered immunity or ETI, upon recognition of specific pathogen-derived effector proteins. ETI’s effectiveness depends on inactivity when the cognate pathogen is absent, rapid induction when a pathogen is recognized and a rapid suppression after induction. The ubiquitin-proteasome pathway, mediated by the sequential actions of E1 (ubiquitin-activating), E2 (ubiquitin-conjugating) and E3 (ubiquitin ligase) enzymes is a major protein modification and degradation pathway found in all eukaryotes. Our preliminary data indicate that maize E3-ligase ZmCER9 mediates degradation of the Rp1-D NLR R-protein, and several other NLR R-proteins, specifically after activation. Based on homology, ZmCER9 is likely a component of the endoplasmic reticulum associated degradation (ERAD), a fundamental eukaryotic quality-control system that degrades incorrectly-folded proteins. ERAD in plants has been poorly characterized and there are no reported substrates of the CER9 complex, meaning that Rp1-D may represent its first known substrate. We hypothesize that ERAD-Mediated Degradation of Activated NLRs (EMDAN) is a general mechanism for the deactivation of ETI in plants. We will use a range of molecular and cell biology techniques to determine the importance of EMDAN and related pathways in controlling ETI in plants and to characterize the role of CER9 in ERAD.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.