AUTHOR=Huang Xingchuan , Liu Yanan , Huang Jianhua , Fernando W. G. Dilantha , Li Xin , Xia Shitou 

TITLE=Activation of NLR-Mediated Autoimmunity in Arabidopsis Early in Short Days 4 Mutant

JOURNAL=Frontiers in Plant Science

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2022.881212

DOI=10.3389/fpls.2022.881212

ISSN=1664-462X

ABSTRACT=<p>From a reverse genetic screen using CRISPR/Cas9 gene editing tool, we unintentionally identified an autoimmune mutant. Map-based cloning and whole-genome sequencing revealed that it contains a deletion in SMALL UBIQUITIN-RELATED MODIFIER (SUMO) protease encoding gene <italic>EARLY IN SHORT DAYS 4</italic> (<italic>ESD4</italic>). Previous studies reported that <italic>esd4</italic> mutants accumulate elevated levels of plant defense hormone salicylic acid (SA). However, upregulated <italic>PATHOGENESIS-RELATED GENE 1</italic> (<italic>PR1</italic>) expression in <italic>esd4</italic> only partly relies on SA level. In this study, we show that plant metabolite N-hydroxypipecolic acid (NHP) biosynthetic genes are upregulated in <italic>esd4</italic>, and NHP biosynthesis mutant <italic>flavin-dependent-monooxygenase 1</italic> (<italic>fmo1</italic>) partially suppresses the autoimmune phenotypes of <italic>esd4</italic>, suggestive of a requirement of NHP signaling for the autoimmunity in <italic>esd4</italic>. As activation of nucleotide-binding leucine-rich repeat immune receptors (NLRs) are associates with the biosynthesis of SA and NHP and lipase-like protein ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1) is a key component downstream of many NLRs, we examined the relationship between EDS1 and ESD4 by analyzing the <italic>eds1 esd4</italic> double mutant. We found that <italic>eds1</italic> largely suppresses <italic>esd4</italic> autoimmunity and blocks the elevated expressions of SA and NHP biosynthesis-related genes in <italic>esd4</italic>. Overall, our study provides evidence supporting the hypothesis that SUMO protease ESD4 likely targets a yet to be identified guardee of NLR by removing its SUMO modification to avoid recognition by the cognate NLR. Loss of ESD4 results in activation of NLR-mediated autoimmunity.</p>