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Title: Maize homologs of CCoAOMT and HCT, two key enzymes in lignin biosynthesis, form complexes with the NLR Rp1 protein to modulate the defense response

Author
item WANG, GUAN-FENG - North Carolina State University
item Balint-Kurti, Peter

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2016
Publication Date: 4/1/2016
Citation: Wang, G., Balint Kurti, P.J. 2016. Maize homologs of CCoAOMT and HCT, two key enzymes in lignin biosynthesis, form complexes with the NLR Rp1 protein to modulate the defense response. Plant Physiology. doi: 10.1104/pp.16.00224.

Interpretive Summary: In this paper we show that a maize resistance protein, Rp1-D attaches to two proteins, hydroxycinnamoyl transferase (HCT) and caffeoyl CoA O-methyltransferase (CCoAOMT) which also can attach to each other. These three proteins for a complex which appears to inhibit the activity of the resistance protein so that it does not induce a defense response. HCT and CCoAOMT are both part of a biochemical pathway that produces lignin and several other chemicals associated with the defense response in plants.

Technical Abstract: Disease resistance (R) genes encode nucleotide binding leucine-rich-repeat (NLR) proteins that confer resistance to specific pathogens. Upon pathogen recognition they trigger a defense response that usually includes a so-called hypersensitive response (HR), a rapid localized cell death at the site of pathogen infection. Intragenic recombination between two maize NLRs, Rp1-D and Rp1-dp2, resulted in the formation of a hybrid NLR, Rp1-D21, which confers an autoactive HR in the absence of pathogen infection. From a previous QTL and genome wide association study, we identified genes encoding two key enzymes in lignin biosynthesis, hydroxycinnamoyl transferase, HCT and caffeoyl CoA O-methyltransferase, CCoAOMT, adjacent to the SNPs which were highly associated with variation in the severity of Rp1-D21-induced HR. We have previously shown that the two maize HCT homologs, suppress the HR conferred by Rp1-D21 in a heterologous system, very likely through physical interaction. Here we show, similarly, that CCoAOMT2 suppress the HR induced by either the full length or by the N-terminal coiled-coil domain of Rp1-D21 also likely via physical interaction and that the metabolic activity of CCoAOMT2 is unlikely to be necessary for its role in suppressing HR. We also demonstrate that CCoAOMT2, HCTs and Rp1 proteins can form a complex(es). A model is derived to explain the roles of CCoAOMT and HCT in Rp1-mediated defense resistance.