Full Title: Maize Homologs of HCT, a Key Enzyme in Lignin Biosynthesis, Bind the NLR Rp1 Proteins to Modulate the Defense Response
Journal: Plant Physiology
Year of Publication: 2015
In plants, most disease resistance (R) genes encode nucleotide binding leucine-rich-repeat (NLR) proteins that trigger a rapid localized cell death called a hypersensitive response (HR) upon pathogen recognition. The maize NLR protein Rp1-D21 derives from an intragenic recombination between two NLRs, Rp1-D and Rp1-dp2, and confers an autoactive HR in the absence of pathogen infection. From a previous QTL and genome wide association study, we identified a SNP locus highly associated with variation in the severity of Rp1-D21-induced HR. Two maize genes encoding hydroxycinnamoyltransferase (HCT, a key enzyme involved in lignin biosynthesis) homologs, termed HCT1806 and HCT4918, were adjacent to this SNP. Here we show that both HCT1806 and HCT4918 physically interact with and suppress the HR conferred by Rp1-D21 but not by other autoactive NLRs when transiently co-expressed in N. benthamiana. Other maize HCT homologs are unable to confer the same level of suppression on Rp1-D21-induced HR. The metabolic activity of HCT1806 and HCT4918 is unlikely to be necessary for their role in suppressing HR. We show that the lignin pathway is activated by Rp1-D21 at both the transcriptional and metabolic levels. We derive a model in which maize HCT1806 and HCT4918 function as guardees or decoys in Rp1-mediated disease resistance.