Utility of Fast Neutron Mutagenesis in Soybean Functional Genomics

Soybean is a major plant source of protein and oil and produces important secondary metabolites beneficial for human health.  Although the soybean genome is large with over 70% of the genes duplicated[1], the gene duplicates, in general, exhibit subfunctionalization suggesting that phenotypically altered mutants can be isolated[2]. To develop a resource for the investigation of soybean gene function, we generated a mutant population using fast neutron irradiation.  Fast neutron mutagenesis is a fast and cost-effective means of generating genome-saturating mutations in plants with large genomes like soybean.  Moreover, fast neutron irradiation induces genomic deletions which can be easily defined using comparative genome hybridization (CGH)[3, 4].   Due to the size of the mutant population and size of the soybean plant, the majority of the phenotypic screening is field-based. For example, initial screens have focused on phenotypic screens that modify plant growth and development, which can be easily screened visually. However, clearly, a major focus needs to be placed on traits of agronomic interest, such as seed traits. Therefore, we have also screened the population using near infrared and nuclear magnetic resonance approaches, which are later verified by chemical analysis. These approaches have identified a variety of seed composition mutants, including those affected in total oil content, total protein content, as well as variation in specific fatty acids. In several cases, the gene mutation responsible for the changes has been identified. These examples clearly show the utility of the fast neutron mutant population for forward genetic screens. .However, we are also developing a database of all of the deletions analyzed from this population. This resource should ultimately be useful for reverse genetic screens for mutations of interest.

1. Schmutz J, Cannon SB, Schlueter J, Ma J, Mitros T, Nelson W, Hyten DL, Song Q, Thelen JJ, Cheng J et al:   Genome sequence of the palaeopolyploid soybean. Nature 2010, 463(7278):178-183.

2. Roulin A, Auer PL, Libault M, Schlueter J, Farmer A, May G, Stacey G, Doerge RW, Jackson SA: The fate of duplicated genes in a polyploid plant genome. The Plant journal : for cell and molecular biology 2012.

3. Bolon YT, Haun WJ, Xu WW, Grant D, Stacey MG, Nelson RT, Gerhardt DJ, Jeddeloh JA, Stacey G, Muehlbauer GJ et al: Phenotypic and genomic analyses of a fast neutron mutant population resource in soybean. Plant physiology 2011, 156(1):240-253.

4. Haun WJ, Hyten DL, Xu WW, Gerhardt DJ, Albert TJ, Richmond T, Jeddeloh JA, Jia G, Springer NM, Vance CP et al: The composition and origins of genomic variation among individuals of the soybean reference cultivar  Williams 82. Plant physiology 2011, 155(2):645-655.