Maize introgression library provides evidence for the involvement of liguleless1 in resistance to northern leaf blight

Authors: KOLKMAN, JUDITH - Cornell University; STRABLE, JOSH - Cornell University; HARLINE, KATE - Cornell University; KROON, DALLAS - Cornell University; WIESNER-HANKS, TYR - Cornell University; Bradbury, Peter; NELSON, REBECCA - Cornell University

Submitted to: Genes, Genomes, Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/21/2020
Publication Date: 8/14/2020
Citation: Kolkman, J.M., Strable, J., Harline, K., Kroon, D.E., Wiesner-Hanks, T., Bradbury, P., Nelson, R.J. 2020. Maize introgression library provides evidence for the involvement of liguleless1 in resistance to northern leaf blight. Genes, Genomes, Genetics. https://doi.org/10.1534/g3.120.401500.
DOI: https://doi.org/10.1534/g3.120.401500

Interpretive Summary: Northern Leaf Blight (NLB) is an economically important disease of maize in the United States and much of the rest of the world. For that reason, genetic sources of resistance to NLB have been studied extensively. Some major genes have been identified but less is known about the genes that have smaller effects but that as a group account for much of the commercially useful resistance. The research described in this paper shows that near-isogenic lines (NILs) are a useful tool for helping to identify genes with smaller effects. In this case, the near isogenic lines are inbred lines mostly idenitical to B73 but with genetic segments or introgressions from other lines. Identifying individual NILs that differ in susceptibility to B73 allows researchers to narrow that resistance down to one or a few small chromosome segments. Combining that information with high density genetic markers showed that the gene liguleless1, which is known to affect leaf architecture, has alleles that affect NLB resistance.

Technical Abstract: Plant disease resistance is largely governed by complex genetic architecture. In maize, few disease resistance loci have been characterized. Near-isogenic lines are a powerful genetic tool to dissect quantitative trait loci. We analyzed an introgression library of maize (Zea mays) near-isogenic lines, termed a nested near-isogenic line library for resistance to northern leaf blight caused by the fungal pathogen Setosphaeria turcica. The population was comprised of 412 BC5F4 near-isogenic lines that originated from 18 diverse donor parents and a common recurrent parent, B73. Single nucleotide polymorphisms identified through genotyping by sequencing were used to define introgressions and for association analysis. Near isogenic lines that conferred resistance and susceptibility to northern leaf blight were comprised of introgressions that overlapped known northern leaf blight quantitative trait loci. Genome-wide association analysis and stepwise regression further resolved five quantitative trait loci regions, and implicated several candidate genes, including Liguleless1, a key determinant of leaf architecture in cereals. Two independently-derived mutant alleles of liguleless1 inoculated with S. turcica showed enhanced susceptibility to northern leaf blight. In the maize nested association mapping population, leaf angle was positively correlated with resistance to northern leaf blight in five recombinant inbred line populations, and negatively correlated with northern leaf blight in four recombinant inbred line populations. This study demonstrates the power of an introgression library combined with high density marker coverage to resolve quantitative trait loci. Furthermore, the role of liguleless1 in leaf architecture and in resistance to northern leaf blight has important applications in crop improvement.