Department of Plant Nutrition, Estación Experimental de Aula Dei-CSIC, Avda. Montañana 1005, 50059, Zaragoza, Spain.
Laboratorio Agroambiental, Gobierno de Aragón, Avda. Montañana 1005, 50071, Zaragoza, Spain.
Plant Mol Biol. 2020 Oct;104(3):283-296. doi: 10.1007/s11103-020-01042-7. Epub 2020 Aug 1.
Differences in FAE1 enzyme affinity for the acyl-CoA substrates, as well as the balance between the different pathways involved in their incorporation to triacylglycerol might be determinant of the different composition of the seed oil in Brassicaceae. Brassicaceae present a great heterogeneity of seed oil and fatty acid composition, accumulating Very Long Chain Fatty Acids with industrial applications. However, the molecular determinants of these differences remain elusive. We have studied the β-ketoacyl-CoA synthase from the high erucic feedstock Thlaspi arvense (Pennycress). Functional characterization of the Pennycress FAE1 enzyme was performed in two Arabidopsis backgrounds; Col-0, with less than 2.5% of erucic acid in its seed oil and the fae1-1 mutant, deficient in FAE1 activity, that did not accumulate erucic acid. Seed-specific expression of the Pennycress FAE1 gene in Col-0 resulted in a 3 to fourfold increase of erucic acid content in the seed oil. This increase was concomitant with a decrease of eicosenoic acid levels without changes in oleic ones. Interestingly, only small changes in eicosenoic and erucic acid levels occurred when the Pennycress FAE1 gene was expressed in the fae1-1 mutant, with high levels of oleic acid available for elongation, suggesting that the Pennycress FAE1 enzyme showed higher affinity for eicosenoic acid substrates, than for oleic ones in Arabidopsis. Erucic acid was incorporated to triacylglycerol in the transgenic lines without significant changes in their levels in the diacylglycerol fraction, suggesting that erucic acid was preferentially incorporated to triacylglycerol via DGAT1. Expression analysis of FAE1, AtDGAT1, AtLPCAT1 and AtPDAT1 genes in the transgenic lines further supported this conclusion. Differences in FAE1 affinity for the oleic and eicosenoic substrates among Brassicaceae, as well as their incorporation to triacylglycerol might explain the differences in composition of their seed oil.
FAE1 酶对酰基辅酶 A 底物的亲和力差异，以及参与其掺入三酰基甘油的不同途径之间的平衡，可能是芸薹属植物种子油组成不同的决定因素。芸薹属植物的种子油和脂肪酸组成具有很大的异质性，积累了具有工业应用价值的超长链脂肪酸。然而，这些差异的分子决定因素仍不清楚。我们研究了来自高芥酸菜籽的β-酮酰基辅酶 A 合酶（Pennycress）。在两个拟南芥背景下（Col-0，其种子油中含有不到 2.5%的芥酸和 FAE1 活性缺乏的 fae1-1 突变体，不积累芥酸），对 Pennycress FAE1 酶进行了功能表征。Pennycress FAE1 基因在 Col-0 中的种子特异性表达导致种子油中芥酸含量增加 3 到 4 倍。这种增加伴随着二十碳烯酸水平的降低，而油酸水平没有变化。有趣的是，当 Pennycress FAE1 基因在 fae1-1 突变体中表达时，二十碳烯酸和芥酸水平只发生了微小的变化，而油酸可供伸长，这表明 Pennycress FAE1 酶对二十碳烯酸底物的亲和力高于拟南芥中的油酸。在转基因系中，芥酸被掺入三酰基甘油中，而在二酰基甘油部分的水平没有显著变化，这表明芥酸优先通过 DGAT1 掺入三酰基甘油。在转基因系中 FAE1、AtDGAT1、AtLPCAT1 和 AtPDAT1 基因的表达分析进一步支持了这一结论。芸薹属植物中 FAE1 对油酸和二十碳烯酸底物的亲和力差异，以及它们掺入三酰基甘油的差异，可能解释了它们种子油组成的差异。
