Abstract
BackgroundThe hypersensitive defense response (HR) in plants is a fast, localized necrotic response around the point of pathogen ingress. HR is usually triggered by a pathogen recognition event mediated by a nucleotide-binding site, leucine-rich repeat (NLR) protein. The autoactive maize NLR gene Rp1-D21 confers a spontaneous HR response in the absence of pathogen recognition. Previous work identified a set of loci associated with variation in the strength of Rp1-D21-induced HR. A polygalacturonase gene homolog, here termed ZmPGH1, was identified as a possible causal gene at one of these loci on chromosome 7.ResultsExpression of ZmPGH1 inhibited the HR-inducing activity of both Rp1-D21 and that of another autoactive NLR, RPM1(D505V), in a Nicotiana benthamiana transient expression assay system. Overexpression of ZmPGH1 in a transposon insertion line of maize was associated with suppression of chemically-induced programmed cell death and with suppression of HR induced by Rp1-D21 in maize plants grown in the field.ConclusionsZmPGH1 functions as a suppressor of programmed cell death induced by at least two autoactive NLR proteins and by two chemical inducers. These findings deepen our understanding of the control of the HR in plants.
Highlights
The hypersensitive defense response (HR) in plants is a fast, localized necrotic response around the point of pathogen ingress
Gene GRMZM2G135763 encodes a polygalacturonase homolog The maize gene GRMZM2G135763 was previously identified as a candidate gene for modulation of HR induced by Rp1-D21 [15] as it spanned a single nucleotide polymorphism (SNP) marker at 121,288, 617 bp on chromosome 7 that was highly associated with variation in this trait (Fig. 1a)
The expression of ZmPGH1 was increased in the field grown plants carrying mu1029380 (Fig. 4b) to approximately the same extent as had been previously observed in plants grown in the growth chamber (Fig. 1c), though the differences were not significant at p < 0.05 due to relatively high variability associated with field assays. These results suggest that higher expression of ZmPGH1 suppresses the effects of Rp1-D21 in maize, which is consistent with the results of mapping, transient expression and chemically induced programed cell death (PCD) experiments described above
Summary
The hypersensitive defense response (HR) in plants is a fast, localized necrotic response around the point of pathogen ingress. HR is usually triggered by a pathogen recognition event mediated by a nucleotidebinding site, leucine-rich repeat (NLR) protein. Previous work identified a set of loci associated with variation in the strength of Rp1-D21-induced HR. The first uses membranebound pattern recognition receptors (PRRs) to detect microbial “marker” molecules often called pathogen- or microbe-associated molecular patterns (PAMPs or MAMPs). This recognition triggers the multi-faceted, relatively low-level, MAMP-triggered immunity (MTI) response, known as basal defense [2]. Some are directly or indirectly recognized by plant resistance (R-) proteins.
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