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

Complex traits governed by many genes can be dissected into more elemental processes under simpler genetic control. Knowledge about elemental processes can help identify physiological strategies that might determine target values for a specific seed trait, such as protein concentration. Our objective, therefore, was to identify genetic variation in elemental processes determining composition and weight of soybean seeds.  Seed composition (e.g. % protein) was dissected in protein, oil and residual contents (mg seed^-1) while weight was dissected into growth rate and duration.
Genetic variation in these traits was studies in a population constructed from parents differing in seed size and composition. 100 F_2:3 lines were sampled each 5-6 days to estimate rate and duration of seed filling.  Mature seeds were analyzed by near infrared reflectance for protein, oil and residual fraction.
We identified two developmental strategies within this population to achieve high seed protein concentration. A subset of “high protein %” lines maintained protein content (mg seed^-1) fairly constant but decreased the content of other seed components (Strategy 1).  A second subset of “high protein %” lines increased protein accumulation (mg seed^-1) (Strategy 2).  Both strategies were attained across a range of seed growth rate and duration, implying some independence between seed development and accumulation of major seed components.  
Current efforts are aimed at creating a QTL association map of the elementary processes that differentiate these developmental strategies.  Identifying different QTLs (and presumably different genes) that might regulate the complex trait of seed protein concentration may provide the genetic basis for overcoming the negative correlation generally observed between protein % and oil %, and between protein % and seed yield.