Mapping Genetic Determinants of Protein and Amino Acid Composition in Bi-Parental G. Max x G. Soja Populations.

Domesticated soybean (Glycine max) seeds are an important source of protein but there is a growing need for soybeans with increased protein content and improved amino acid profiles due in large part to the negative genetic correlation between seed yield and seed protein content.  Soybean meal must also be supplemented with synthetic amino acids (i.e. cysteine, methionine, lysine, and threonine) to meet the dietary requirements of monogastric animals.  The objective of this research is to identify novel genetic determinants of protein and amino acid composition using bi-parental G. max x G. soja populations, genomic sequencing and 6K SNP chip data, and wet-lab analytics.  G. soja lines with favorable protein and amino acid content were identified and the most interesting lines, as well as the G. max parents, were sequenced at 15x coverage on a HiSeq 4000 using 150 paired-end reads.  Two F_5:6 recombinant inbred line (RIL) populations derived from crosses between Williams 82 and two G. soja lines, PI 464890B and PI 458536, were harvested in 2015 and evaluated for protein content using Near Infrared Spectroscopy (NIR: FOSS XDS Rapid Content Analyzer) in combination with maturity and selection index data. Preliminary results reveal a moderate negative correlation between the selection index and protein composition for PI 458536 RILs (r(128) = -0.60, p < 0.01) and a low negative correlation between protein composition and maturity date for PI 464890B RILs (r(144) = -0.35, p < 0.01).  Therefore, the genetic determinants of protein composition are retained in our RIL populations but possibly at the expense of incorporating domestication and maturity loci.  We are currently examining seed protein and amino acid composition using wet-lab chemistry and extracting DNA for evaluation via 6K SNP Infinium chips for the bulk segregant QTL analyses and for detecting known domestication, maturity, and protein and amino acid composition loci.  This research will provide insight into the location of novel protein and amino acid loci from G. soja and the corresponding relationship with domestication and maturity loci in G. max.