Unraveling and exploiting mechanisms of disease resistance in cereal crops is currently limited by their large repeat-rich genomes and the lack of genetic recombination or cultivar (cv)-specific sequence information. We cloned the first leaf rust resistance gene Rph1 (Rph1a) from cultivated barley (Hordeum vulgare) using "MutChromSeq," a recently developed molecular genomics tool for the rapid cloning of genes in plants. Marker-trait association in the CI 9214/Stirling doubled haploid population mapped Rph1 to the short arm of chromosome 2H in a physical region of 1.3 megabases relative to the barley cv Morex reference assembly. A sodium azide mutant population in cv Sudan was generated and 10 mutants were confirmed by progeny-testing. Flow-sorted 2H chromosomes from Sudan (wild type) and six of the mutants were sequenced and compared to identify candidate genes for the Rph1 locus. MutChromSeq identified a single gene candidate encoding a coiled-coil nucleotide binding site Leucine-rich repeat (NLR) receptor protein that was altered in three different mutants. Further Sanger sequencing confirmed all three mutations and identified an additional two independent mutations within the same candidate gene. Phylogenetic analysis determined that Rph1 clustered separately from all previously cloned NLRs from the Triticeae and displayed highest sequence similarity (89%) with a homolog of the Arabidopsis (Arabidopsis thaliana) disease resistance protein 1 protein in Triticum urartu In this study we determined the molecular basis for Rph1-mediated resistance in cultivated barley enabling varietal improvement through diagnostic marker design, gene editing, and gene stacking technologies.
MutChromSeq is an approach for isolation of genes and DNA sequences controlling gene expression in plants with complex and polyploid genomes. It involves a lossless complexity reduction by flow cytometric chromosome sorting and shotgun sequencing DNA from isolated chromosomes. Comparison of sequences from wild-type parental chromosome with chromosomes from multiple independently derived mutants identifies causative mutations in a single candidate gene or a noncoding sequence. MutChromSeq does not rely on recombination-based genetic mapping and does not exclude any DNA sequence from being targeted.
- MeSH
- Chromosomes, Plant genetics MeSH
- DNA, Plant genetics MeSH
- Genome, Plant MeSH
- Genomics methods MeSH
- In Situ Hybridization, Fluorescence methods MeSH
- Mutation * MeSH
- Polyploidy MeSH
- Flow Cytometry methods MeSH
- Gene Expression Regulation, Plant MeSH
- Plants genetics MeSH
- Sequence Analysis, DNA methods MeSH
- Publication type
- Journal Article MeSH
Identification of causal mutations in barley and wheat is hampered by their large genomes and suppressed recombination. To overcome these obstacles, we have developed MutChromSeq, a complexity reduction approach based on flow sorting and sequencing of mutant chromosomes, to identify induced mutations by comparison to parental chromosomes. We apply MutChromSeq to six mutants each of the barley Eceriferum-q gene and the wheat Pm2 genes. This approach unambiguously identified single candidate genes that were verified by Sanger sequencing of additional mutants. MutChromSeq enables reference-free forward genetics in barley and wheat, thus opening up their pan-genomes to functional genomics.
