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Title: Maize homologs of HCT, a key enzyme in lignin biosynthesis, bind the NLR Rp1 proteins to modulate the defense response

Author
item WANG, GUAN-FENG - North Carolina State University
item HE, YIJIAN - North Carolina State University
item STRAUCH, RENE - North Carolina State University
item OLUKOLU, BODE - North Carolina State University
item NIELSEN, DAHLIA - North Carolina State University
item LI, XU - North Carolina State University
item Balint-Kurti, Peter

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/8/2015
Publication Date: 9/15/2015
Citation: Wang, G., He, Y., Strauch, R., Olukolu, B., Nielsen, D., Li, X., Balint Kurti, P.J. 2015. Maize homologs of HCT, a key enzyme in lignin biosynthesis, bind the NLR Rp1 proteins to modulate the defense response. Plant Physiology. 169:2230-2243.

Interpretive Summary: In this paper we look at a protein that confers an autoactive defense (a kind of autoimmunity) response in maize (or corn). We show that the protein, called Rp1-D21 interacts with another protein in the cell that is involved with the biosynthesis of lignin. This interaction appears to inhibit the autoactive activity of Rp1-D21. We suggest there is a link between the resistance response and the phenylpropanoid pathway, which is involved on the biosynthesis of lignin and many other secondary metabolites including several implicated in plant defense.

Technical Abstract: In plants, most disease resistance (R) genes encode nucleotide binding leucine-rich-repeat 42 (NLR) proteins that trigger a rapid localized cell death called a hypersensitive response (HR) 43 upon pathogen recognition. The maize NLR protein Rp1-D21 derives from an intragenic 44 recombination between two NLRs, Rp1-D and Rp1-dp2, and confers an autoactive HR in the 45 absence of pathogen infection. From a previous QTL and genome wide association study, we 46 identified a SNP locus highly associated with variation in the severity of Rp1-D21-induced HR. 47 Two maize genes encoding hydroxycinnamoyltransferase (HCT, a key enzyme involved in lignin 48 biosynthesis) homologs, termed HCT1806 and HCT4918, were adjacent to this SNP. Here we 49 show that both HCT1806 and HCT4918 physically interact with and suppress the HR conferred 50 by Rp1-D21 but not by other autoactive NLRs when transiently co-expressed in N. benthamiana. 51 Other maize HCT homologs are unable to confer the same level of suppression on Rp1-D21- 52 induced HR. The metabolic activity of HCT1806 and HCT4918 is unlikely to be necessary for 53 their role in suppressing HR. We show that the lignin pathway is activated by Rp1-D21 at both 54 the transcriptional and metabolic levels. We derive a model to explain the roles of HCT1806 and 55 HCT4918 in Rp1-mediated disease resistance.