New research published in the Journal of Experimental Botany describes the discovery of new alleles that could lead to soybean varieties with higher stearate levels in the oil and good agronomics.
For many years, plant biotechnologists and breeders have been developing new soybean varieties with enhanced seed oil content and composition. Unfortunately, these advances have sometimes come with undesirable side effects on plant growth, yield, and subsequent market value. Recently published research begins to unravel some of the relationships between oil composition and yield, and allows the use of more selective modifications to enhance the benefits while avoiding the side effects.
The soybean genome is complex; there are five separate genes for stearoyl-acyl carrier protein desaturase (SACPD), the enzyme that begins the process of creating unsaturated fatty acids from stearic acid. Comparative genomics analysis indicated that SACPD genes, labeled GmSACPD-A, B, C, D, and E, were duplicated and derived from a common ancestor that is still present in chlorophytic algae. However, due to its dual role in both seed and nodule development, all currently described varieties with mutations in GmSACPD-C are of extremely poor agronomic value as a result of defective nodulation. Unfortunately, this is the vast majority of currently available varieties.
Researchers in Illinois, Tennessee, Texas, North Carolina, Missouri, Nebraska and France applied a technique called TILLING by Target Capture Sequencing (Tilling-by-Sequencing), which is a versatile extension of the conventional TILLING by sequencing method. When applied to the soybean genome, this method successfully identified 12, 14, and 18 EMS mutants at the GmSACPD-A, -B, and -D genes, respectively. Functional analysis of all identified mutants revealed that while they play an unprecedented role in unsaturated fatty acid biosynthesis, they do not affect nodule development or plant structure, indicating that the different versions of the gene may have specialized functions. The fact that GmSACPD-C is highly expressed in both seeds and nodules explains the effect on yield. This discovery will allow the development of new, high stearic acid soybean lines without affecting nitrogen-fixing nodules, thus removing the negative impact on yield. The next steps to further characterize these lines and begin the process of combining these new stearic acid genes in order to develop new high stearic acid varieties are already underway.
The research article detailing these findings is entitled “Soybean TILLING-by-sequencing+ reveals the role of novel GmSACPD members in the unsaturated fatty acid biosynthesis while maintaining healthy nodules” and published in the Journal of Experimental Botany at https://doi.org/10.1093/jxb/eraa402. It was based on research supported by USB Project number 2020-162-0127.
A commentary providing context and highlighting this top-tier research was also published in that issue as “Improving soybean seed oil without poor agronomics” by Miguel Alfonso of the Department of Plant Nutrition, Estación Experimental de Aula Dei – Consejo Superior de Investigaciones Científicas in Zaragoza, Spain (https://doi.org/10.1093/jxb/eraa407).