Mutant-assisted exploration of natural variation underlying R gene-mediated immunity in maize

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PI: Gurmukh (Guri) S. Johal, Purdue UniversityCo-PI: Clifford F. Weil, Purdue UniversityCo-PI: James. W. Moyer, North Carolina State UniversityCo-PI: Peter J. Balint-Kurti, North Carolina State UniversityPlant disease resistance (R) genes encode proteins that respond to pathogen invasion by triggering a rapid, localized "hypersensitive reaction" (HR), in which host tissue immediately adjacent to the site of infection undergoes programmed cell death. Although, HR is a fundamental part of the immune response in plants, very little is known about the genes that trigger, signal, execute, and then contain it. Exhaustive mutagenesis screens have been conducted in Arabidopsis, but have turned up only a few genes linked to HR, possibly because of genetic redundancy or lethality of HR mutants. An alternate and potentially huge resource of HR variation is available in natural germplasm. If effectively tapped and delineated, this resource has the potential to advance considerably our understanding of HR . By taking advantage of a constitutive-active allele of the Rp1 gene, which confers resistance to the common rust disease of maize, we have demonstrated that the maize germplasm contains vast amounts of variation capable of impacting HR. This project will test the broad use of an innovative approach, which looks for naturally occurring alleles that suppress mutant phenotypes to rapidly detect and explore natural variation underlying HR. Using this approach, one HR-modulating locus (Hrml1) has already been identified and mapped in a preliminary test using the IBM population of maize; this QTL will be cloned. In addition, many more QTL will be identified and characterized by broadening the screen to the 5000-line Nested Association Mapping (NAM) population currently available to the maize community. The broader impacts of the project are many-fold. First, the approach of discovering and harnessing genetic diversity is likely to be broadly applicable to a large number of important traits in most plant species. Second, an outreach component will bring the uses of biodiversity to middle school curricula (Grades 6-8) and the topics of DNA sequence analysis and quantitative trait analysis to high school curricula, with the development and test of teaching materials that can be widely distributed. Third, these teaching modules will be developed for and with students from a wide range of cultural, racial and educational backgrounds, and their teachers. This approach will allow development of several versions of these modules, using different examples, different assessments and different forms of presentation so that they can be applied effectively in a variety of settings. The goal is to overturn the stereotype that these subjects are too complex for middle and high school students to grasp, and to prime student to investigate plant diversity and genetics in greater detail later in their education so that they are better able to understand the issues. These topics are not generally covered in most science curricula at these levels, despite their increasing importance scientifically and socially. The outcomes and biological resources generated by this project will be available through the project website: http://www.Rp1-MAGIC.purdue.edu.