Institut de Biologie Moléculaire des Plantes du CNRS, Université de Strasbourg, Département Réseaux Métaboliques Végétaux, F-67083 Strasbourg cedex, France.
Plant Physiol. 2010 Jan;152(1):107-19. doi: 10.1104/pp.109.145672. Epub 2009 Nov 18.
Genes encoding sterol ester-forming enzymes were recently identified in the Arabidopsis (Arabidopsis thaliana) genome. One belongs to a family of six members presenting homologies with the mammalian Lecithin Cholesterol Acyltransferases. The other one belongs to the superfamily of Membrane-Bound O-Acyltransferases. The physiological functions of these genes, Phospholipid Sterol Acyltransferase1 (PSAT1) and Acyl-CoA Sterol Acyltransferase1 (ASAT1), respectively, were investigated using Arabidopsis mutants. Sterol ester content decreased in leaves of all mutants and was strongly reduced in seeds from plants carrying a PSAT1-deficient mutation. The amount of sterol esters in flowers was very close to that of the wild type for all lines studied. This indicated further functional redundancy of sterol acylation in Arabidopsis. We performed feeding experiments in which we supplied sterol precursors to psat1-1, psat1-2, and asat1-1 mutants. This triggered the accumulation of sterol esters (stored in cytosolic lipid droplets) in the wild type and the asat1-1 lines but not in the psat1-1 and psat1-2 lines, indicating a major contribution of the PSAT1 in maintaining free sterol homeostasis in plant cell membranes. A clear biological effect associated with the lack of sterol ester formation in the psat1-1 and psat1-2 mutants was an early leaf senescence phenotype. Double mutants lacking PSAT1 and ASAT1 had identical phenotypes to psat1 mutants. The results presented here suggest that PSAT1 plays a role in lipid catabolism as part of the intracellular processes at play in the maintenance of leaf viability during developmental aging.
基因编码固醇酯形成酶最近在拟南芥（Arabidopsis thaliana）基因组中被鉴定出来。一个属于具有哺乳动物卵磷脂胆固醇酰基转移酶同源性的六个成员家族。另一个属于膜结合 O-酰基转移酶超家族。使用拟南芥突变体研究了这些基因（磷脂固醇酰基转移酶 1（PSAT1）和酰基辅酶 A 固醇酰基转移酶 1（ASAT1））的生理功能。所有突变体的叶片固醇酯含量降低，携带 PSAT1 缺陷突变的植物种子中的固醇酯含量严重降低。所有研究品系的花朵中的固醇酯含量非常接近野生型。这表明固醇酰基化在拟南芥中具有进一步的功能冗余。我们进行了喂食实验，向 psat1-1、psat1-2 和 asat1-1 突变体中提供固醇前体。这引发了野生型和 asat1-1 系中固醇酯（储存在细胞质脂滴中）的积累，但在 psat1-1 和 psat1-2 系中没有，表明 PSAT1 在维持植物细胞膜中游离固醇稳态方面的主要作用。与 psat1-1 和 psat1-2 突变体中缺乏固醇酯形成相关的一个明显的生物学效应是早期叶片衰老表型。缺乏 PSAT1 和 ASAT1 的双突变体与 psat1 突变体具有相同的表型。这里提出的结果表明，PSAT1 在脂质分解代谢中发挥作用，作为维持发育衰老过程中叶片活力的细胞内过程的一部分。
