The storage of lipids is a crucial mechanism conserved across diverse organisms. Lipid droplets (LDs) are important organelles for storing lipids in cells, and there are many proteins interspersed with their outer phospholipid membranes. SEIPIN, as a LD protein, has been reported to influence the size and number of LDs, and to affect neutral lipid storage in Arabidopsis. In Brassica napus (B. napus), there are three SEIPIN genes, including SEIPIN1 (4 copies), SEIPIN2 (4 copies), and SEIPIN3 (2 copies). The transcriptome databases show that BnaSEIPIN1 only has high expression in late developing seeds, BnaSEIPIN2 has low expression almost in all tissues, while BnaSEIPIN3 has negligible expression across all tissues. BnaC03.SEIPIN1 and BnaA09.SEIPIN2 were cloned to be overexpressed in B. napus seeds specifically. The results showed that BnaC03.SEIPIN1 increased the oil content of seeds by 4.3–5.4% and the thousand-seed weight by 0.43—0.49 g. However, no significant effect of BnaA09.SEIPIN2 on oil content was observed. Further studies revealed that BnaC03.SEIPIN1 significantly increased the number of small and large LDs, but not affected the LDs size. The qRT-PCR results showed that the expression levels of some key genes related to lipid synthesis and storage were altered significantly between overexpression lines and WT. Taking together, above results reveal that SEIPIN1 improves seed oil content accumulation by the number of small and larger LDs, but not by influencing LDs size. Our results provide a new understanding on SEIPIN regulating seed oil accumulation in Brassica napus.
Li et al. (Wed,) studied this question.