Wax synthases from sunflower (Helianthus annuus) seeds.

Wax esters (WEs) are aliphatic esters of very-long-chain fatty acids and fatty alcohols that contribute to the lipid coatings of many plant organs. In the case of sunflower seeds, these compounds accumulate especially in the seed hull and are synthesized by the action of wax synthase (WS) enzymes through the esterification of acyl-CoA derivatives with very-long-chain fatty alcohols produced by fatty acyl reductases. Here, genes encoding 15 WSs were identified in the sunflower genome, of which 3 are expressed appreciably in the seed during the period of WE accumulation: HaWS6, HaWS8, and HaWS11. The localization and structure of these WSs were studied, and they were expressed in yeast in order to assay the microsome fractions prepared from them. The HaWSs all had very broad specificity profiles for alcohols and they were able to esterify short-chain alcohols (<10 C) with the acyl-CoA supplied. Indeed, simultaneous expression of HaWS8 and HaFAR5 resulted in the production in yeast of some WEs typically present in the sunflower hull.