Natural variation in expression of the HECT E3 ligase UPL3 influences seed size and crop yields in Brassica napus by altering regulatory gene expression.

Identifying genetic variation that increases crop yields is a primary objective in plant breeding. We have used association analyses of Brassica napus (oilseed rape/canola) accessions to identify genetic variation in the promoter of a HECT E3 ligase gene, BnaUPL3.C03, that influences seed size and final yield. We establish a mechanism in which UPL3 mediates the proteasomal degradation of LEC2, a master regulator of seed maturation. Reduced UPL3 expression increases LEC2 protein levels and prolongs the expression of lipid biosynthetic genes and seed maturation. Natural variation in BnaUPL3.C03 expression has not yet been exploited in current Brassica napus breeding lines and can thus be used as a new approach to maximize future yields in this important oil crop.