Very-long-chain fatty acid diversity in nine Heliophila seed oils

Heliophila is a genus of approximately 90 recognized plant species endemic to southern Africa and considered the most morphologically diverse genus in the family Brassicaceae. To begin to characterize chemical diversity in the genus, seed oil content and fatty acid composition were determined for 9 species, with representatives from the three major recognized clades. All species produced very-long-chain fatty acids (VLCFAs) as major components of the seed triacylglycerol (TAG) oil, with considerable diversity of fatty acid chain length. The 22-carbon (C22) monounsaturated fatty acid erucic acid (cis-13-docosenoic acid) was the dominant VLCFA in the oil of Heliophila coronopifolia at 47.6% of total seed fatty acids whereas the unusual C26 fatty acid ximenic acid (cis-17-hexacosenoic acid) dominated the VLCFA profile of oil from Heliophila scoparia at 35.8%. Heliophila africana oil was identified as a potential novel source of the nutraceutical fatty acid, nervonic acid (cis-15-tetracosenoic acid). Analysis of the oil of 3 species by sn-1,3 regioselective lipase digestion demonstrated the virtual exclusion of VLCFAs from the sn-2 position of TAG. Examination of the oil from H. scoparia by Matrix-Assisted Laser Desorption/Ionization Time-of-Flight (MALDI-TOF) Mass Spectrometry revealed the presence of high molecular weight TAGs and widespread distribution of VLCFAs among the TAG molecular species. Heliophila species have significant potential as sources of novel seed oil enriched in VLCFAs and as model species to study the mechanisms and evolution of VLCFA biosynthesis in plants.