Slabaugh M B, Leonard J M, Knapp S J
Department of Crop and Soil Science, Oregon State University, Corvallis 97331, USA.
Plant J. 1998 Mar;13(5):611-20. doi: 10.1046/j.1365-313x.1998.00065.x.
Seed oils of most Cuphea species contain > 90% medium chain (C8-C14) fatty acids. Thioesterases with specificity for these substrates are important determinants of the medium chain phenotype. The role of condensing enzymes, however, has not been investigated. cDNA clones encoding beta-ketoacyl-acyl carrier protein (ACP) synthase (KAS) were isolated from C. wrightii, a C10/C12-producing species. Deduced amino acid sequences of four unique clones were approximately 60% identical to plant KAS I sequences and approximately 75% identical to a distinct class of KAS sequences recently identified in castor and barley. A 46 kDa protein that was observed only in developing and mature seed was detected using antiserum directed against recombinant Cuphea KAS protein. The 46 kDa protein was abundant in developing seeds of six medium chain-producing Cuphea species but barely detected in one long chain-producing species. A 48 kDa protein identified immunologically as KAS I was expressed in both medium and long chain-producing Cuphea species and was detected in all tissues tested. In in vitro assays, extracts from C. wrightii and C. viscosissima developing embryos were unable to extend fatty acid chains beyond C10 following treatment with 10 microns cerulenin, a potent inhibitor of KAS I. However, a C. viscosissima mutant, cpr-1, whose seed oils are deficient in caprate relative to wild type, was impaired in extension of C8 to C10 in this assay and Western analysis revealed a specific deficiency in 46 kDa KAS in cpr-1 embryos. These results implicate cerulenin-resistant condensing activity in production of medium chain fatty acids in Cuphea.
大多数萼距花属植物的种子油含有超过90%的中链（C8 - C14）脂肪酸。对这些底物具有特异性的硫酯酶是中链表型的重要决定因素。然而，缩合酶的作用尚未得到研究。从产C10/C12的赖氏萼距花中分离出编码β-酮酰基-酰基载体蛋白（ACP）合酶（KAS）的cDNA克隆。四个独特克隆推导的氨基酸序列与植物KAS I序列约60%相同，与最近在蓖麻和大麦中鉴定出的一类不同的KAS序列约75%相同。使用针对重组萼距花KAS蛋白的抗血清检测到一种仅在发育中和成熟种子中出现的46 kDa蛋白质。这种46 kDa蛋白质在六种产中链的萼距花属植物的发育种子中含量丰富，但在一种产长链的植物中几乎检测不到。一种经免疫鉴定为KAS I的48 kDa蛋白质在产中链和长链的萼距花属植物中均有表达，且在所有测试组织中都能检测到。在体外试验中，用10微米的浅蓝菌素（一种KAS I的有效抑制剂）处理后，赖氏萼距花和粘萼距花发育胚的提取物无法将脂肪酸链延长至超过C10。然而，粘萼距花的一个突变体cpr - 1，其种子油中癸酸盐相对于野生型有所缺乏，在该试验中C8到C10的延长受到损害，Western分析显示cpr - 1胚中46 kDa KAS存在特异性缺陷。这些结果表明，在萼距花中，对浅蓝菌素耐药的缩合活性与中链脂肪酸的产生有关。
