Unraveling Genomic Complexity at a Quantitative Disease Resistance Locus in Maize Jun 19,2014 Tiffany M. Jamann1, Jesse A. Poland2, Judith M. Kolkman1,Laurie G. Smith3 and Rebecca J. Nelson1,*
- Cornell University; 2 Kansas State University; 3 University of California, San Diego
Multiple disease resistance has important implications for plant fitness, given the selection pressure that many pathogens exert directly on natural plant populations and indirectly via variety improvement programs on crop plants. Evidence of a locus conditioning resistance to multiple pathogens was found in bin 1.06 of the maize genome with the allele from inbred line ‘Tx303’ conditioning quantitative resistance to northern leaf blight (NLB) and qualitative resistance to Stewart’s wilt. To dissect the genetic basis of resistance in this region and to refine candidate gene hypotheses, we mapped resistance to the two diseases. Both resistance phenotypes were localized to overlapping regions, with the Stewart’s wilt interval refined to a 95.9-kb segment containing three genes, and the NLB interval to a 3.60-Mb segment containing 117 genes. Regions of the introgression showed little to no recombination, suggesting structural differences between the inbred lines ‘Tx303’ and ‘B73’, the parents of the fine-mapping population. We examined copy number variation across the region using next-generation sequencing data and found large variation in read depth in ‘Tx303’ across the region relative to the reference genome of inbred line ‘B73’. In the fine-mapping region, association mapping for NLB implicated candidate genes, including a putative zinc finger and pan1. We tested mutant alleles and found that pan1 is a susceptibility gene for NLB and Stewart’s wilt. Our data strongly suggest that structural variation plays an important role in resistance conditioned by this region, and pan1, a gene conditioning susceptibility for NLB, may underlie the QTL.