Biogenesis and regulation of oil bodies during early stage seed formation in Brassica napus

Rapeseed is one of the most important oil crops in China. Most oil in rapeseed is stored in the oil bodies. In this paper, the biogenesis of oil bodies and gene expression level variations in oil body proteins and fatty acid synthesis transcription factors were investigated during embryogenesis in two Brassica napus L. cultivars (‘Westar’ and ‘Topas’) via ultrastructural observation and real-time fluorescence quantitative PCR. Results showed that oil bodies existed in early embryos of B. napus, even in the embryo proper and suspensor, 9-11 d after pollination (globular embryo stage). The gene expression level of all oil body proteins (oleosins, steroleosins, and BnCLO1), except BnCLO3, increased at the heart embryo stage and continued to increase during the embryonic development stage. The gene expression levels of fatty acid synthesis transcription factors (BnLEC1, BnL1L, BnWRI1, and BnFUS3) increased at the early stages and decreased at the late stages, but their peak times were different. The gene expression level of BnLEC1 peaked first, followed by BnL1L, BnWRI1, and BnFUS3 last. Our results showed that oil bodies exist in early embryos of B. napus, even at the globular-embryo stage, and the gene expression level of their structural proteins and transcription factors increases from the heart-embryo stage.