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. Our initial screens have focused on phenotypes 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 also screened the population for alterations in seed composition by near infrared and nuclear magnetic resonance spectroscopy, which were later verified by chemical analysis [5]. These approaches identified a variety of seed composition mutants, including those affected in total oil, protein and vitamin E content, as well as variations in specific fatty acids. In several cases, the gene mutation responsible for the phenotype has been identified. Putative copy number variations (CNVs) ranged in size from 989 bp to 9.6 Mb, with a mean size of 540 kb. The number of genes located within each CNV ranged from zero to 232, with an average of 13 genes per deletion and 36 genes per mutant line. Bulked mutant seeds are available to the soybean community upon request (contact staceyg@missouri.edu). CNVs will be available through Soybase (http://soybase.org) and SoyKB (http://soykb.org). 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 2013, 73: 143–153 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. 5. Gillman JD., Stacey MG, Cui Y, Berg H, Stacey G. Deletions of the SACPD-C locus elevate seed stearic acid levels but also result in fatty acid and morphological alterations in nitrogen fixing nodules. BMC Plant Biol. 2014 (in press)