Identification of a Maize Locus That Modulates the Hypersensitive Defense Response, Using Mutant-Assisted Gene Identification and Characterization

Abstract

Potentially useful naturally occurring genetic variation is often difficult to identify as the effects of individual genes are subtle and difficult to observe. In this study, a novel genetic technique called MutantAssisted Gene Identification and Characterization is used to identify naturally occurring loci modulating the hypersensitive defense response (HR) in maize. Mutant-Assisted Gene Identification and Characterization facilitates the identification of naturally occurring alleles underlying phenotypic variation from diverse germplasm, using a mutant phenotype as a ''reporter.'' In this study the reporter phenotype was caused by a partially dominant autoactive disease resistance gene, Rp1-D21, which caused HR lesions to form spontaneously all over the plant. Here it is demonstrated that the Rp1-D21 phenotype is profoundly affected by genetic background. By crossing the Rp1-D21 gene into the IBM mapping population, it was possible to map and identify Hrml1 on chromosome 10, a locus responsible for modulating the HR phenotype conferred by Rp1-D21. Other loci with smaller effects were identified on chromosomes 1 and 9. These results demonstrate that Mutant-Assisted Gene Identification and Characterization is a viable approach for identifying naturally occurring useful genetic variation.

Maize Homologs of CCoAOMT and HCT, Two Key Enzymes in Lignin Biosynthesis, Form Complexes with the NLR Rp1 Protein to Modulate the Defense Response

“…Rp1-D21 causes an autoactive HR lesion phenotype in the absence of pathogen infection. Several other hallmarks of the pathogen-induced defense response are also associated with Rp1-D21-mediated HR phenotype in maize, including high accumulation of H 2 O 2 and increased expression of defense-related genes (Chintamanani et al, 2010). The Rp1-D21 HR lesion phenotype is influenced by light, temperature, and genetic background (Chintamanani et al, 2010;Negeri et al, 2013).…”

“…We used Rp1-D21 as a tool to investigate the genetic basis of the control of HR by crossing a line carrying it into several mapping populations to identify loci, pathways, and genes associated with modulation of the HR strength (Chintamanani et al, 2010;Chaikam et al, 2011;Olukolu et al, 2013Olukolu et al, , 2014. One of the populations used, called the nested association mapping (NAM) population, is an extremely large and powerful mapping population that allows the mapping of quantitative trait loci (QTL) with high precision (McMullen et al, 2009).…”

Maize Homologs of HCT, a Key Enzyme in Lignin Biosynthesis, Bind the NLR Rp1 Proteins to Modulate the Defense Response

“…Rp1-D21, a mutant conferring an autoactive HR lesion phenotype in the absence of pathogen infection, was formed by unequal crossing over at the Rp1 locus and subsequent intragenic recombination between Rp1-D and Rp1-dp2 (Sun et al, 2001;Smith et al, 2010). Several other hallmarks of the pathogen-induced immune response, including hydrogen peroxide accumulation and increased expression of the defense-related genes PR1, PRms, and WIP1 (for wound-induced protein1), are also associated with Rp1-D21-mediated lesion phenotype in maize (Chintamanani et al, 2010).…”

“…The severity of Rp1-D21 HR lesion phenotype is affected by temperature, light, and importantly, genetic background (Chintamanani et al, 2010;Negeri et al, 2013). We have used Rp1-D21 as a tool to identify loci associated with modulation of the strength of HR segregating in several mapping populations (Chintamanani et al, 2010;Chaikam et al, 2011;Olukolu et al, 2013Olukolu et al, , 2014.…”

“…We have used Rp1-D21 as a tool to identify loci associated with modulation of the strength of HR segregating in several mapping populations (Chintamanani et al, 2010;Chaikam et al, 2011;Olukolu et al, 2013Olukolu et al, , 2014. One of the populations used, called the nested association mapping (NAM) population, is an extremely large and powerful mapping population that allows the mapping of quantitative trait loci with high precision (McMullen et al, 2009).…”