Modulation of fatty acid elongation enhances hydroxy fatty acid biosynthesis and accumulation in Arabidopsis

Seed oils of castor (Ricinus communis) and lesquerella (Physaria fendleri) mainly contain hydroxy fatty acids (HFAs) useful in industrial applications. As castor seeds contain toxin ricin and lesquerella is not yet a commercial crop, extensive efforts have been directed to develop safe commercial sources of HFAs in Arabidopsis (Arabidopsis thaliana). We over-expressed a lesquerella elongase, PfKCS18, in a previous transgenic Arabidopsis pCam5 line which expresses five castor genes. pCam5+PfKCS18 increased lesquerolic acid at the expense of ricinoleic acid without changing the total HFA content. Over-expressing PfKCS18 in a previously line pCam5-atfae1, where an endogenous elongase gene is knocked-out in pCam5, the total HFA content increased from 30% to 35% in pCam5-atfae1+PfKCS18. pCam5+PfKCS18 and pCam5-atfae1+PfKCS18 fully recovered the adverse effects of HFA on the seed size and weight. Seed germination was restored fully in pCam5-atfae1+PfKCS18 and partially in pCam5+PfKCS18. Similarly, pCam5-atfae1+PfKCS18 recovered the numbers of leaves and siliques, while pCam5+PfKCS18 partially restored on leave numbers and fully on the inflorescence length. Seed yield was reduced in transgenics with the most reduction in pCam5 and the least in pCam5-atfae1+PfKCS18. Our results provide insights to understanding the mechanism of HFA biosynthesis in Arabidopsis and directs future research on engineering effective HFA-producing oilseeds.