Fine Mapping and Genome Characterization of the Net Form Net Blotch Susceptibility Locus on Barley

Net form net blotch (NFNB), caused by the necrotrophic fungus Pyrenophora teres f. teres (Ptt), is a major foliar disease of barley. Dominant and recessive resistance has been mapped in globally diverse barley lines, often times to a centromeric region of barley chromosome 6H. Barley cultivars Rika and Kombar harbor two dominant genes, Spt.r and Spt.k, conferring susceptibility to Ptt isolates 6A and 15A, respectively. Spt.r and Spt.k, previously known as rpt.k and rpt.r, were mapped to a ~3.3 cM region on barley chromosome 6H in a Rika x Kombar doubled haploid mapping population. Synteny analysis shows a high level of colinearity between barley and Brachypodium gene order within this region. Utilizing the syntenic relationship with Brachypodium, STS and PCR-GBS markers were developed to saturate the region. Fine mapping of Spt.r/Spt.k locus in a population of 2976 recombinant gametes utilizing these newly developed markers delimited Spt.r and Spt.k to ~0.07 cM and ~0.23 cM, respectively. The barley chromosome 6H BAC minimum tiling path pools, developed by INRA, in addition to barley next-generation sequencing data are being used to aid in the construction of a physical map across the two susceptibility loci. Through allele analysis of diverse barley lines, a strong candidate Spt.k gene, predicted to encode a membrane bound extracellular LRR, has been identified and characterized. The predicted 438 amino acid protein contains a conserved C-terminal LRR and a diverged N-terminus. Validation will be attempted through the creation of deletion mutants via TALENs.