An LRR-only protein promotes NLP-triggered cell death and disease susceptibility by facilitating oligomerization of NLP in Arabidopsis.

Necrosis- and ethylene-inducing peptide 1 (Nep1)-like proteins (NLPs) constitute a superfamily of proteins toxic to dicot plants and the molecular basis of its toxicity is still obscure. Using quantitative trait loci (QTL) analysis we investigated the genetic variation underlying ion leakage in Arabidopsis plants elicited with MoNLP1 derived from Magnaporthe oryzae. The QTL conditioning MoNLP1 toxicity was positionally cloned and further characterized to elucidate its mode of action. MoNLP1-triggered cell death varied significantly across >250 Arabidopsis accessions and three QTLs were identified conferring the observed variation. The QTL on chromosome 4 was uncovered to encode an LRR-only protein designated as NTCD4, which shares high sequence identity with a set of nucleotide-binding leucine-rich repeat proteins. NTCD4 was secreted into the apoplast and physically interacted with multiple NLPs. Apoplastic NTCD4 facilitated NLPs' oligomerization which was closely associated with toxicity in planta. The natural genetic variation causing D3N change in NTCD4 reduced the secretion efficiency of NTCD4 and the infection of Botrytis cinerea on Arabidopsis plants. These observations demonstrate that the plant-derived NTCD4 is recruited by NLPs to promote toxicity via facilitating their oligomerization, which extends the understandings of a key step in the NLPs' toxic mode of action.