Location: Plant Genetics Research
2018 Annual Report
Objectives
Objective 1: Identify new soybean alleles, or effective combinations of existing genes, that positively impact commercially relevant oil or meal traits; work with breeders to incorporate them into modern backgrounds; confirm their expression or effectiveness under field conditions; and determine value in food or feed applications.
Objective 2: Identify and verify new genomic regions in soybean associated with improved stress tolerance, seed constituent (oil and protein), and quality traits, and use genomic strategies such as genetic mapping and genome analysis to make new genes rapidly available to breeders.
Objective 3: Develop novel strategies to increase concentrations of S-containing amino acids and to reduce levels of trypsin inhibitor and allergens; work with breeders to develop soybean germplasm that combine these genes in high protein backgrounds to meet the animal nutrient requirements.
Approach
Obj 1- New soybean germplasm will be developed with combinations of the high oleic-low linolenic oil trait and low raffinose oligosaccharide meal trait that is targeted to different maturity groups (MG). Seeds produced in an appropriate environment will be evaluated for trait interactions, environmental stability, protein and oil content, and yield. We will establish a novel panel of approximately 400 soybean accessions from the National Plant Germplasm System (NPGS) and conduct genome-wide association studies (GWAS) with protein and oil data. Mutant soybean lines will be screened to identify seed composition variants.
Obj 2- We will use a four pronged approach in order to dissect the genetic architecture underlying soybean seed value (principally seed oil and protein content) and abiotic stress adaptation: 2.1) a new GWAS using a diverse panel of 380 MG III genotypes to maximize genetic diversity within a very narrow maturity range; 2.2) Genomic Prediction to estimate seed composition breeding values for all 2,011 MG III accessions; 2.3) Fine mapping of a heat-tolerance trait from an exotic landrace; and 2.4) Development of a Multi-Parent Advanced Generation Inter-Cross (MAGIC) population. We will evaluate the potential of Genomic Prediction to predict seed composition and select parents with maximal genetic potential for developing a MAGIC population. We will Fine-map a previously identified major effect QTL associated with tolerance to heat-induced-seed-degradation.
Obj 3- We will develop and characterize soybean germplasm with increased sulfur (S)-containing amino acids and decreased anti-nutritional factors. To enhance the S amino acid content, we plan to overexpress an enzyme in the sulfur assimilation pathway. Additionally, high-protein soybean experimental lines lacking Kunitz trypsin inhibitor (KTI) and ß-conglycinin, will be developed using a traditional breeding approach. In order to verify if overexpression of tow enzymes simultaneously will further increase the overall S-amino acid content, we will characterize ATPS and OASS activity in greenhouse grown material from genetic crosses between overexpressing transgenic soybeans lines. To better understand the chilling stress responses in soybean, a comparative proteomic analysis will be performed.
Progress Report
Progress towards Objective 1 has been initiated. The project objectives are dependent on a successful field season for initiating new breeding populations, maturity confirmation of experimental lines, development of seed for composition analyses, and preliminary yield evaluations for existing soybean oil plus meal trait lines. All of those experiments are progressing according to schedule. Seed protein and oil content were determined for the set of about 400 lines with seed produced in one environment. A set of approximately 2000 mutant lines was screened for protein and oil content, and three lines were identified that exceeded the selection criteria. No plants from those lines emerged in the field. However, Near Infrared Reflectance spectroscopy equations are now available for soybean seed protein and oil content that account for varieties with the high oleic seed oil trait based on expanded utilization of the trait.
Progress was made on all Objective 2 milestones, however insufficient time (7 months) has passed to fully meet the 12 month milestone. Substantial progress has been made toward the 12 month milestone for Subobjective 2.1; data collection was completed for two of the three locations of our multi-year Genome Wide Association Study and a third location is nearly complete. Likewise, genotypic data collection is in process. When complete an unprecedented level of detail for soybean genes which control seed value traits will be available.
Previous studies have shown overexpression of a specific enzyme in plants increases the production of cysteine and glutathione and protect the plants against environmental stress. To increase the biosynthesis of cysteine and methionine in soybean, we are attempting to overexpress the enzyme to provide increased metabolic flux through the pathway. Earlier, we have cloned and characterized the chloroplast-localized enzyme from soybean. Utilizing this cloned soybean enzyme, we have made several constructs for soybean transformation which were used for seed-specific expression, as well as constitutive expression. To distinguish the introduced enzyme in transgenic plants from the native enzyme, we have introduced a tag at the C-terminus of the enzyme. These constructs have been transferred into Agrobacterium tumefaciens and are currently being used for transformation of soybean.
Accomplishments
1. Improvement of soybean seed composition. Soybean meal is considered as “gold standard” to which other protein sources are compared. Sulfur-containing amino acids, cysteine and methionine, play a vital role in human health and nutrition. Unfortunately, the concentration of these two amino acids in soybean does not meet the optimum levels required for animal nutrition. On account of this deficiency, concerted efforts have been made to increase the concentrations of cysteine and methionine in soybean seeds. ARS scientists in Columbia, Missouri, published a critical review article that is insightful and describes missing experiments needed to advance the improvement of soybean seed composition. This article showed the strengths and weaknesses of different approaches in elevating the sulfur amino acid content of soybeans and highlighted recent studies targeting key sulfur assimilatory enzymes and the manipulation of sulfur metabolism in transgenic soybeans to improve the nutritive value of soybean proteins. Information from this review article will assist researchers in the development of high yielding U.S. soybean cultivars with improved nutritive value. At a time when U.S. soybean meal is facing increasing competition from alternative feed ingredients and other soybean producing countries, it would benefit U.S. soybean farmers if soybeans with improved nutritive value can be developed for both food and animal feed.
