1a. Objectives (from AD-416)
Investigate the genetic mechanisms by which the plant hormones abscisic acid (ABA) and gibberellin (GA) control pre-harvest sprouting stand establishment, and drought and cold tolerance in wheat and model organisms. Develop and utilize molecular markers for the western region wheat and barley breeding programs for resistance to stem rust, other biotic and abiotic stresses, and end-use quality. Develop wheat cultivars with durable resistance to stripe rust, stem rust, soilborne diseases, cold and drought, and improved end-use quality for Western Region cropping systems using wheat germplasm resources from the USDA-ARS National Small Grains Germplasm Collection (NSGC) and other national and international sources.
1b. Approach (from AD-416)
Determine whether ABA sensitivity controls grain dormancy and tolerance to preharvest sprouting. Determine whether degree of drought tolerance and cold tolerance tend to correlate with each other and depend upon ABA sensitivity. Determine how GA signaling controls seed dormancy and plant height. Identify and use new and existing molecular markers linked to genes for biotic stress resistance, specifically for stripe rust resistance. Identify and use new molecular markers for genes linked to abiotic and end-user quality. Establish and use high-throughput molecular marker analysis systems to track the segregation of important genes in wheat and barley breeding programs. Characterize core wheat germplasm sets for use in identifying haplotypes important in Western Regional germplasm adaptation. Use molecular markers to link genotypes to phenotypes while maintaining critical haplotypes for enhancement, disease resistance and end-use quality in Western Region wheat breeding programs. Identify new sources of genes giving superior end-use quality, disease resistance, and resistance to cold and drought.
3. Progress Report
Objective 1A addresses whether the plant hormone abscisic acid (ABA) controls wheat grain dormancy and preharvest sprouting tolerance. ABA insensitive mutants of hard red spring Scarlet wheat showed decreased seed dormancy and rapid after-ripening, whereas ABA hypersensitive mutants of soft white spring Zak show increased seed dormancy and resistance to preharvest sprouting. Objective 1B examined whether ABA controls wheat resistance to drought and cold stress. The ABA insensitive mutations showed no decrease in drought tolerance. The ABA hypersensitive mutant ZakERA19 has increased drought tolerance resulting from decreased water use. A high yielding cultivar, Louise, appears to resist drought via higher ABA sensitivity resulting in higher water use efficiency. Objective 1C examines how the hormone Gibberellin (GA) controls seed dormancy and plant height. DELLA proteins repress seed germination. DELLA proteins are destroyed by F-box protein SLY1 and SNE, only when DELLA forms a complex including the DELLA, the F-box protein, and the GA receptor. Objective 2A Identify and use molecular markers for biotic stress resistance, abiotic stress and end-use quality. The Western Regional Small Grains Genotyping laboratory coordinated single nucleotide polymorphism (SNP) discovery efforts on 1,824 wheat lines including 6 mapping populations, the resulting 9.5 million datapoints are currently being evaluated for efficacy in each of the breeding programs. Objective 2B 485,065 datapoints were scored in molecular marker analysis systems to track the segregation of important genes in the 5 state breeding programs. Objective 2C Characterize core wheat germplasm for use in identifying haplotypes important in Western Regional germplasm: Germplasm from the NSGC that was screened in Kenya for UG99 resistance was characterized with SSR markers and a molecular phylogeny was developed which was used to indicate novel resistance germplam. In addition 50 of these lines were genotyped with the 9K SNP and these markers are currently being used in association mapping and the development of 2 molecular maps. Objective 3 Develop wheat germplasm and cultivars adapted to Western Region cropping systems with resistance to stripe rust, soilborne disease, cold, drought, and with improved end-use quality and to coordinate the Western Regional Cooperative Wheat Nurseries. ARS-Amber soft white winter wheat and ARS97-163-4C winter club wheat were increased for breeders seed at Othello WA. Both have excellent resistance to predominant races of stripe rust and excellent end use quality. Marker assisted selection was used to select several hundred breeding lines with combined resistance to stripe rust, barley yellow dwarf virus, pre-harvest sprouting and soil-borne disease. The Western Regional Nurseries were evaluated at ten locations in the Northwest. Data was collected on agronomic traits, resistance to stripe, stem and leaf rust, Hessian fly, and cold. This work will benefit wheat growers and end users because competitive soft wheat cultivars can be grown with reduced inputs and marketed as premium quality products.
1. The role of abscisic acid (ABA) in wheat drought tolerance. Understanding the mechanisms supporting higher wheat yield under drought stress is essential. The spring wheat variety Louise shows higher water use efficiency and higher efficiency of light use during photosynthesis under water stress. These phenotypes correlated with higher sensitivity to the plant stress hormone ABA. This research was used to develop new strategies to map and breed genes for drought tolerance.
2. Gibberellin (GA) signaling controls seed germination and plant height. The mechanisms by which the GA stimulates seed germination and stem elongation are unknown. ARS scientists in Pullman, WA showed that GA stimulates seed germination and plant growth by causing two F-box proteins, SLEEPY1 and SNEEZY, to target master negative regulators called DELLA for protein destruction. This gene/protein family is termed DELLA reference to the highly conserved regulatory amino acid sequence D-E-L-L-A (Aspartic acid-Glutamic acid-Leucine-Leucine-Alanine). SNEEZY destroys the subset of DELLA proteins that control plant height, but not the DELLAs that control seed germination. This fact provides a new mutation breeding strategy to alter F-box genes to make shorter plants which resistant to lodging without causing problems with poor germination and seedling emergence.
3. Development of ARS Amber soft white winter wheat. The problem is that changes in the stripe rust population structure caused susceptible reactions on several new soft white winter wheat cultivars in the Pacific Northwest. The bulk pedigree breeding method combined with marker assisted selection was used to develop ARS Amber. This cultivar has excellent resistance to stripe rust, combined with excellent agronomic and end use quality characteristics that will reduce grower risks for production and marketing. This research will benefit growers and end users by saving money on fungicide sprays and providing wheat grain that is highly marketable.
4. Identification of loci associated with agronomic traits in adapted spring wheat. Having a better understanding on the genetic control of agronomic traits is necessary because it is the most important criteria for crop improvement. Using a population developed from two widely grown spring wheat cultivars, ARS researchers in conjunction with researchers at Washington State University reported that photoperiod insensitivity had an important effect on several agronomic traits especially when high temperatures or drought limited the grain filling period. This research is important because identification of loci affecting important agronomic traits allows breeders to make gains from direct and indirect selection to improve complex traits like grain yield.
5. Developing molecular markers in wheat. In cereals the current sets of molecular markers are based on microsatellites which reside in the regions of the genome between genes. In order to obtain a higher density of polymorphic markers more likely to reside within genes or in gene-rich regions, information from relevant US germplasm was used to identify new single nucleotide polymorphisms and develop single nucleotide polymorphism (SNP) based molecular markers. 1,824 wheat lines including 6 mapping populations were tested for 9,000 potentially polymorphic SNPs by ARS scientists in Pullman, WA. 5,232 new polymorphic SNP markers were identified, of which 4,143 were placed on the 6 genetic maps. The resulting 9.5 million datapoints are currently being utilized by breeding programs. These new SNP markers will accelerate breeding programs by supporting efforts to identify markers tightly linked to important genes, and by enabling breeders to implement less expensive genome-wide selection strategies.Ariizumi, T., Steber, C.M. 2011. Mutations in the F-box gene SNEEZY result in decreased arabidopsis GA signaling. Plant Signaling and Behavior. 6(6):831-833.