Overexpression of Seipin1 Increases Oil in Hydroxy Fatty Acid-Accumulating Seeds.

While plant oils are an important source of food, plants also produce oils containing specialized fatty acids with chemical and physical properties valued in industry. Ricinoleic acid, a hydroxy fatty acid (HFA) produced in the seed of castor (Ricinus communis), is of particular value, with a wide range of applications. Since castor cultivation is currently successful only in tropical climates, and because castor seed contain the toxin ricin, there are ongoing efforts to develop a temperate crop capable of HFA biosynthesis. In castor, ricinoleic acid is incorporated into triacylglycerol (TAG) which accumulates in the seed lipid droplets. Research in the model plant Arabidopsis (Arabidopsis thaliana) has successfully produced HFA constituting 30% of the total seed oil, but this is far short of the level required to engineer commercially viable crops. Strategies to increase HFA have centered on co-expression of castor TAG biosynthesis enzymes. However, since lipid droplets are the location of neutral lipid storage, manipulating droplets offers an alternative method to increase oil that contains specialized fatty acids. The Arabidopsis Seipin1 protein modulates TAG accumulation by affecting lipid droplet size. Here, we overexpress Seipin1 in a hydroxylase-expressing Arabidopsis line, increasing seed HFA by 62% and proportionally increasing total oil. Increased seed oil was concomitant with a 22% increase in single seed weight and a 69% increase in harvest weight, while seed germination rose by 45%. Because Seipin1 function is unaffected by the structure of the HFA, these results demonstrate a novel strategy that may increase accumulation of many specialized seed oils.