Instituto de la Grasa (CSIC), Edificio 46, Campus Universitario Pablo de Olavide, Ctra. de Utrera Km 1, 41013, Seville, Spain.
Departamento de Genética, Facultad de Biología, Universidad de Sevilla, 41012, Seville, Spain.
Planta. 2019 Jun;249(6):1823-1836. doi: 10.1007/s00425-019-03126-1. Epub 2019 Mar 7.
The enzymes HaKCS1 and HaKCS2 are expressed in sunflower seeds and contribute to elongation of C18 fatty acids, resulting in the C20-C24 fatty acids in sunflower oil. Most plant fatty acids are produced by plastidial soluble fatty acid synthases that produce fatty acids of up to 18 carbon atoms. However, further acyl chain elongations can take place in the endoplasmic reticulum, catalysed by membrane-bound synthases that act on acyl-CoAs. The condensing enzymes of these complexes are the ketoacyl-CoA synthase (KCSs), responsible for the synthesis of very long chain fatty acids (VLCFAs) and their derivatives in plants, these including waxes and cuticle hydrocarbons, as well as fatty aldehydes. Sunflower seeds accumulate oil that contains around 2-3% of VLCFAs and studies of the fatty acid elongase activity in developing sunflower embryos indicate that two different KCS isoforms drive the synthesis of these fatty acids. Here, two cDNAs encoding distinct KCSs were amplified from RNAs extracted from developing sunflower embryos and named HaKCS1 and HaKCS2. These genes are expressed in developing seeds during the period of oil accumulation and they are clear candidates to condition sunflower oil synthesis. These two KCS cDNAs complement a yeast elongase null mutant and when expressed in yeast, they alter the host's fatty acid profile, proving the encoded KCSs are functional. The structure of these enzymes was modelled and their contribution to the presence of VLCFAs in sunflower oil is discussed based on the results obtained.
HaKCS1 和 HaKCS2 这两种酶在葵花籽中表达，对 C18 脂肪酸的延伸有贡献，从而产生葵花籽油中的 C20-C24 脂肪酸。大多数植物脂肪酸是由质体可溶性脂肪酸合酶产生的，该酶可产生长达 18 个碳原子的脂肪酸。然而，进一步的酰基辅酶 A 延长可以在内质网中进行，由膜结合的合酶催化，这些合酶作用于酰基辅酶 A。这些复合物的缩合酶是酮酰基辅酶 A 合酶（KCS），负责植物中非常长链脂肪酸（VLCFAs）及其衍生物的合成，这些衍生物包括蜡质和角质烃，以及脂肪酸醛。向日葵种子积累的油中含有约 2-3%的 VLCFAs，对发育中的向日葵胚胎中脂肪酸延长酶活性的研究表明，两种不同的 KCS 同工型驱动这些脂肪酸的合成。在这里，从发育中的向日葵胚胎提取的 RNA 中扩增了两个编码不同 KCS 的 cDNA，并分别命名为 HaKCS1 和 HaKCS2。这些基因在油积累期间在发育中的种子中表达，它们是调节向日葵油合成的明确候选基因。这两个 KCS cDNA 互补酵母延长酶缺失突变体，当在酵母中表达时，它们改变宿主的脂肪酸谱，证明编码的 KCS 是功能性的。对这些酶的结构进行了建模，并根据获得的结果讨论了它们对向日葵油中 VLCFAs 存在的贡献。
