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 the toxin ricin and lesquerella is not yet a commercial crop, extensive efforts have been directed toward developing safe commercial sources of HFAs in Arabidopsis. We overexpressed a lesquerella elongase, PfKCS18, in a previous transgenic Arabidopsis pCam5 line that expresses five castor genes. pCam5+PfKCS18 increased lesquerolic acid at the expense of ricinoleic acid without changing the total HFA content. Overexpressing PfKCS18 in a previous line, pCam5-atfae1, where an endogenous elongase gene is knocked out in pCam5 (pCam5-atfae1+PfKCS18), the total HFA content was increased from 30% to 35%. pCam5+PfKCS18 and pCam5-atfae1+PfKCS18 did not show the adverse effects of HFA on 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 leaf numbers and fully restored 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 into the mechanism of HFA biosynthesis in Arabidopsis and direct future research on engineering effective HFA-producing oilseeds.