Molecular-assisted breeding for soybean with high oleic/low linolenic acid and elevated vitamin E in the seed oil.

The uses of vegetable oils are determined by functional properties arising from their chemical composition. Soybean oil was previously used in margarines and baked foods after partial hydrogenation to achieve heat and oxidative stability. This process, however, generates trans fats that are now excluded from food use because of cardiovascular health risks. Also present in soybean oil are the anti-oxidant tocopherols, with α-tocopherol (vitamin E) typically present as a minor component compared to γ-tocopherol. Genetic improvement of the fatty acid profile and tocopherol profile is an attractive solution to increase the functional and health qualities of soybean oil. The objective of this research was to develop resources to directly select with molecular markers for the elevated vitamin E trait in soybean oil and to use a molecular breeding approach to combine elevated vitamin E with the high oleic/low linolenic acid seed oil trait that improves oil functionality and nutrition. New soybean germplasm was developed from the molecular breeding strategy that selected for alleles of six targeted genes. Seed oil from the novel soybean germplasm was confirmed to contain increased vitamin E α-tocopherol along with a high oleic acid/low linolenic acid profile.

Molecular-assisted breeding for improved carbohydrate profiles in soybean seed.

KEY MESSAGE: Two independent variant raffinose synthase 3 (RS3) alleles produced an equivalent phenotype and implicated the gene as a key contributor to soybean seed carbohydrate phenotype. Soybean is an important crop because the processed seed is utilized as a vegetable oil and a high protein meal typically used in livestock feeds. Raffinose and stachyose, the raffinose family of oligosaccharides (RFO) carbohydrate components of the seed, are synthesized in developing soybean seeds from sucrose and galactinol. Sucrose is considered positive for metabolizable energy, while RFO are anti-nutritional factors in diets of monogastric animals such as humans, poultry, and swine. To increase metabolizable energy available in soybean seed meal, prior research has been successful in deploying variant alleles of key soybean raffinose synthase (RS) genes leading to reductions or near elimination of seed RFO, with significant increases in seed sucrose. The objective of this research was to investigate the specific role of variants of the RS3 gene in a genomic context and improve molecular marker-assisted selection for the ultra-low (UL) RFO phenotype in soybean seeds. The results revealed a new variant of the RS3 allele (rs3 snp5, rs3 snp6) contributed to the UL RFO phenotype when mutant alleles of RS2 were present. The variant RS3 allele identified was present in about 15% of a small set of soybean cultivars released in North America. A missense allele of the RS3 gene (rs3 G75E) also produced the UL RFO phenotype when combined with mutant alleles of RS2. The discoveries reported here enable direct marker-assisted selection for an improved soybean meal trait that has the potential to add value to soybean by improving the metabolizable energy of the meal.

Classification of distinct seed carbohydrate profiles in soybean.

Soybeans are an important source of protein-rich meal for livestock feed formulations. Recent changes in the cost of commodity-based sources of metabolizable energy (ME) inputs has put pressure on soybean meal to deliver both protein and ME in feed formulations. The non-oil fraction of soybean contains approximately 12% soluble carbohydrates, principally sucrose, raffinose, and stachyose. Of these carbohydrates, only sucrose is positive for ME. Both raffinose and stachyose, belonging to the raffinose family of oligosaccharides (RFOs), are considered antinutritional because of the negative consequences of their fermentation in the gut of monogastric animals when RFOs are consumed in the diet. Therefore, there is an interest in improving soybean seed composition so that it contains higher ME and fewer antinutritional components by increasing the sucrose content while lowering the RFOs. Several soybean lines have been discovered that contain altered levels of RFOs, and recent molecular genetic investigations have shown the phenotype to be caused by mutations in a raffinose synthase 2 (RS2) gene encoding the enzyme that is the committed step for RFO biosynthesis. The objective of this research was to determine the variation in carbohydrate profile for different soybean lines grown in a single location containing one of three different alleles of the RS2 gene. The results indicate that, although there is variation in the carbohydrate profiles for each line, different lines with the same RS2 genotype tend to produce a characteristic carbohydrate profile. Although the carbohydrate profile for each RS2 genotype class was consistent in different genetic backgrounds under two conditions grown at one location, more research will be necessary to determine the environmental stability of the carbohydrate profiles in multiple locations over different years.

Genetic interactions between brassinosteroid-inactivating P450s and photomorphogenic photoreceptors in Arabidopsis thaliana.

Plants use light as a source of information via a suite of photomorphogenic photoreceptors to optimize growth in response to their light environment. Growth-promoting hormones such as brassinosteroids also can modulate many of these responses. BAS1 and SOB7 are brassinosteroid-catabolizing P450s in Arabidopsis thaliana that synergistically/redundantly modulate photomorphogenic traits such as flowering time. The role of BAS1 and SOB7 in photomorphogenesis has been investigated by studying null-mutant genetic interactions with the photoreceptors phyA, phyB, and cry1 with regard to seed germination and flowering time. The removal of BAS1 and/or SOB7 rescued the low germination rate of the phyA-211 phyB-9 double-null mutant. With regard to floral induction, bas1-2 and sob7-1 showed a complex set of genetic interactions with photoreceptor-null mutants. Histochemical analysis of transgenic plants harboring BAS1:BAS1-GUS and SOB7:SOB7-GUS translational fusions under the control of their endogenous promoters revealed overlapping and distinct expression patterns. BAS1's expression in the shoot apex increases during the phase transition from short-to-long-day growth conditions and requires phyB in red light. In summary, BAS1 and SOB7 displayed both simple and complex genetic interactions with the phytochromes in a plant-stage specific manner.

The MYB23 gene provides a positive feedback loop for cell fate specification in the Arabidopsis root epidermis.

The specification of cell fates during development requires precise regulatory mechanisms to ensure robust cell type patterns. Theoretical models of pattern formation suggest that a combination of negative and positive feedback mechanisms are necessary for efficient specification of distinct fates in a field of differentiating cells. Here, we examine the role of the R2R3-MYB transcription factor gene, AtMYB23 (MYB23), in the establishment of the root epidermal cell type pattern in Arabidopsis thaliana. MYB23 is closely related to, and is positively regulated by, the WEREWOLF (WER) MYB gene during root epidermis development. Furthermore, MYB23 is able to substitute for the function of WER and to induce its own expression when controlled by WER regulatory sequences. We also show that the MYB23 protein binds to its own promoter, suggesting a MYB23 positive feedback loop. The localization of MYB23 transcripts and MYB23-green fluorescent protein (GFP) fusion protein, as well as the effect of a chimeric MYB23-SRDX repressor construct, links MYB23 function to the developing non-hair cell type. Using mutational analyses, we find that MYB23 is necessary for precise establishment of the root epidermal pattern, particularly under conditions that compromise the cell specification process. These results suggest that MYB23 participates in a positive feedback loop to reinforce cell fate decisions and ensure robust establishment of the cell type pattern in the Arabidopsis root epidermis.