Pathology, Genomics, & Molecular Biology
The PPG combines traditional plant pathology and cutting edge genomics approaches to discover, understand, and access novel disease resistance genes for crop improvement. We specialize in species comprising the potato tertiary genepool, a group of primitive diploid potato species collectively known as superseries Stellata. These species are rich source of genes for resistance to diseases and environmental stresses, with the potential to improve the cultivated potato. Other facets of our research develop and employ comparative genomics approaches to study whole genome organization throughout the genus Solanum and the family Solanaceae.
Current research projects in our laboratory include:
1. Gene Discovery:
Anticipatory Cloning: We are developing efficient mapping and gene isolation methods to access agriculturally significant genes found in the potato tertiary genepool. We refer to our approach as “anticipatory cloning” since candidate disease resistance genes are first identified on the basis of DNA sequence and later linked to a phenotypic function. Using the disease resistant Solanum bulbocastanum as a model species, we are developing an integrated series of linkage maps and candidate resistance gene physical maps. Associated with each resistance gene physical map are markers suitable for rapid and efficient mapping across populations and in related species. Our approach will allow researchers to quickly map genes conditioning disease resistance by targeting genome regions with a probable effect. Once a specific genome region has been identified, associated candidate gene physical maps will serve as starting points for positional cloning efforts.
Mapping of candidate disease resistance genes: We have developed novel and highly efficient mapping methods to integrate linkage maps and candidate disease resistance gene physical maps. Using our approach, SNPs (single nucleotide polymorphisms) between mapping population parents are targeted for marker design. The resulting markers are then used to genetically map BAC clones containing candidate disease resistance genes. Upper fragment (a) is an internal control ( RNA Polymerase II ). Lower fragment (b) was developed from BAC sequence, is associated with late blight resistance gene RB , and segregates in our mapping population at a 1:1 ratio (54:54 observed; not shown).
Phenotypic Screening: Our gene discovery efforts also entail germplasm screening at the phenotypic level. We use a variety of approaches including field, greenhouse, and laboratory-based tests. Current emphasis includes systematic characterization of superseries Stellata for resistance to foliar late blight and Verticillium wilt. To learn more about our phenotypic disease resistance screening efforts, check out our Germplasm page.
Solanum polyadenium: a source of genes for late blight resistance. A single genotype of S. polyadenium in our late blight nursery at Rosemount , MN . The field was inoculated three weeks prior with the late blight pathogen, P. infestans US8. Solanum polyadenium remains disease free, while cultivated potato (rows bordering S. polyadenium ) have died from disease.
2. Understanding Gene Function:
Disease Resistance in the Agricultural Setting: The potato tertiary genepool is a rich source of disease resistance genes. The foliar late blight resistance gene RB was cloned from the wild potato S. bulbocastanum. Our laboratory is now leading efforts to understand how RB can be best used in an agricultural context. We have completed a multi-year study of potato cultivars carrying the RB gene, demonstrating that the gene imparts strong resistance, even in the absence of fungicides. We have also developed highly specific PCR and RT-PCR assays to study this gene in a variety of potato backgrounds. We are using our assays to examine the effects of gene copy number on disease resistance and to understand how gene transcription is affected by the age of the plant and by environmental factors. We are also examining whether RB, which imparts disease resistance to the foliage, functions to impart disease resistance to the tuber.
Genetic improvement of cultivated potato: genes from the potato tertiary genepool in action. Our late blight screening nursery at Rosemount , MN. Three weeks prior to the photo, the field was inoculated with P. infestans US8. No fungicides were applied. Rows of green and healthy potatoes, each carrying the RB gene, are bordered by dead and brown potatoes lacking this resistance gene.
3. Accessing Useful Genes:
Allelic Mining: We have optimized long-range PCR for the isolation of alleles at the late blight resistance locus RB from multiple genotypes of the wild potato Solanum bulbocastanum. We have demonstrated that alleles at this locus are broadly distributed throughout the genotypic and geographic range of this species. We have discovered unique alleles that are thought to have arisen through an inter-genic recombination event, suggesting that recombination between structurally related loci might be an important factor in generating allelic diversity at the RB locus. The alleles we have cloned using this approach may function to impart late blight resistance and may have unique disease resistance specificities. Importantly, our efforts have made these alleles available for improvement of the cultivated potato for the very first time. The strategic deployment of different RB alleles or pyramiding multiple RB alleles in a single potato genotype may enhance long-term durability in the agricultural setting.
Want to know more about our research? Check out our recent Publications and Presentations & Posters.
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