2013 Annual Report
1a.Objectives (from AD-416):
Objective 1: Identify and characterize genes or gene products that control metabolic expression of protein and oil accumulation during legume seed development.
Objective 2: Develop genomic resources to characterize the function of genes or gene products that mediate genetic variation in composition and allergenicity of seed storage proteins in soybean and comparable legumes.
1b.Approach (from AD-416):
The project uses molecular biological approaches to study the sequence and expression of genes that are required for soybean seed development. Genetic and biochemical approaches are used to study the interactions and function of gene products that are important for the accumulation of storage proteins or fatty acids in seeds. Genetic approaches are used to create mutant plants and characterize mutant plants in the TILLING population.
This project had two related objectives which would further our understanding of genes involved in both the protein and fatty acid aspects soybean seed composition. The first objective included molecular biological characterization of several transcription factors that were expected to have a function in the determination of seed composition. cDNAs were isolated for multiple transcriptional regulators, however efforts to further evaluate the effect of these factors on seed composition were postponed to expand on the genetic approaches which were part of the second objective.
The second objective was to further develop the soybean mutant population in forward and reverse genetics to identify genes and generate new germplasm that could be used in soybean improvement. As part of this objective, we evaluated the use of next generation sequencing technologies for mutation discovery in soybean. We were able to identify some best practices that will be used to streamline future experiments in mutation discovery and mapping. As part of the forward genetics screen to discover new genes and new alleles that result in soybean with altered composition, the project identified new alleles in 6 distinct enzymes that were previously known to be involved in fatty acid biosynthesis:
1. Mutations in KASIIa, which result in increased levels of palmitic acid.
2. Mutations which reduce levels of the saturated fat palmitic acid for a healthier soybean oil.
3. Mutations which result in increased levels of oleic acid.
4. A mutation which results in lower levels of linolenic acid which improves soybean oil stability.
5. Mutations in SACPD-C which result in increased levels of stearic acid in soybean seeds. These lines are being evaluated for agronomic characteristics and can be used alone or in combination by breeders to generate soybeans with a variety of useful composition traits
In addition, we are still working to identify additional genes by conventional genetic mapping that result in reduced linolenic acid, increased oleic acid, increased stearic acid, and changes in the overall protein and oil level of the soybean seed that do not correspond to any known genes previously described in soybean. The mutant population was also screened by ARS scientists in Missouri to identify mutants that have alterations in seed ion content, and remains a resource that is available for screening by others in the soybean community.
Genes that result in increased levels of stearic acid in soybean seeds. Soybean oil is a valuable commodity with use primarily in food products for human consumption. Current commodity soybeans contain only 3-4% stearate. During this project period ARS scientists at West Lafayette, Indiana identified 6 mutant lines that carry mutations in a gene known to control stearate levels, and result in levels of seed stearic acid of up to 13%. Other lines in the lab were identified that contain as much as 20% stearic acid, and genetic mapping is underway to identify the genes that may contribute to this trait. Increasing the level of the saturated fatty acid stearate in soybean oil could enable soybean oil to be used as a multifunctional baking fat.