Identification of Elemental Physiological Processes Controlling Genetic Variation in Soybean Seed Composition.

Complex traits governed by many genes can be dissected into more elemental processes. For example, final protein concentration (SPC) in soybean seeds is determined predominately by accumulation (mg/seed) of protein, oil and carbohydrate components. Increases in SPC can arise from increases in protein synthesis or by reductions in oil and carbohydrate accumulation. Likewise, component accumulation can be further dissected into rate and duration of net synthesis.  As such, similar values for SPC can result from a variety of developmental and metabolic strategies.  We have identified two such strategies to achieve high SPC within a population of F2 families segregating for SPC.  A subset of high SPC lines increased protein accumulation per se (mg/seed) (Strategy 1).  A second subset of high SPC lines maintained protein content (mg/seed) fairly constant but decreased the content of other seed components (Strategy 2).  These lines were screened with SSR markers to identify genomic regions associated with these two unique strategies. At some genomic regions, alleles from one parent determined one type of strategy while alleles from the other parent determined the other strategy.   These results imply that different suites of genes determine these alternative strategies for achieving high SPC. Because different alleles at the same genomic region are responsible for high SPC, breeding may favor those that are not linked to reduced oil synthesis or seed yield.  If so, identifying these genes opens the possibility to overcome the commonly observed negative correlations between SPC, oil, and grain yield.