UBIQUITIN PROTEIN LIGASE 3 – A novel regulator of yield in Brassica napus

Abstract: Identifying and using genetic variation that contributes to crop yield is a key aim in the breeding of major food and industrial crops such as oilseed rape (OSR). Using Associative Transcriptomics we screened a panel of OSR accessions for genetic variation associated with a range of yield component traits. This analysis identified a locus associated with the weight of seed per pod. The expression of a gene at this locus, encoding an orthologue of the Arabidopsis UBIQUITIN PROTEIN LIGASE 3 (UPL3), correlated negatively with the observed trait variation. Concordant with this result, we show that Arabidopsis upl3 mutants lacking a functional copy of this gene produce significantly larger seeds relative to WT plants. This increase in seed size was coupled with a 12% increase in seed storage protein and a 13% increase in seed lipid levels. Assessment of gene expression throughout seed development revealed that a set of regulatory transcription factor genes known for their role in seed maturation are upregulated in upl3 mutant seeds relative to WT. Using a cell-free system we showed that UPL3 mediates the proteosomal degradation of the protein encoded by LEAFY COTYLEDON 2 (LEC2), a master regulator of seed maturation. Closer inspection of the promoter region of the Brassica napus orthologue of UPL3 revealed extensive variation which may be causal for the differential expression and consequent phenotypic variation observed. Such variation could be utilised in breeding programs for the direct selection of genotypes exhibiting large seed size with high lipid content.

Host: Andrea Harper