Targeted mutations of BnPAP2 lead to a yellow seed coat in Brassica napus L.

The yellow seed trait is preferred by breeders for its potential to improve the seed quality and commercial value of Brassica napus. In the present study, we produced yellow seed mutants using a CRISPR/Cas9 system when the two BnPAP2 homologs were knocked out. Histochemical staining of the seed coat demonstrated that proanthocyanidins accumulation was significantly reduced in the pap2 double mutants and decreased especially in the endothelial and palisade layer cells of the seed coat. Transcriptomic and metabolite profiling analysis suggested that the disruption of BnPAP2 genes could reduce the expression of structural and regulated genes in phenylpropanoid and flavonoid biosynthetic pathways. The broad suppression of these genes might hinder proanthocyanidins accumulation during seed development, causing yellow seed trait in B. napus. These results indicate that BnPAP2 might play a vital role in the regulatory network controlling proanthocyanidins accumulation.