Bayon Shen, Chen Guanqun, Weselake Randall J, Browse John
Institute of Biological Chemistry, Washington State University, Pullman, Washington 99164-6340 (S.B., J.B.); andAlberta Innovates Phytola Centre, Department of Agricultural, Food, and Nutritional Science, University of Alberta, Edmonton, Alberta, Canada T6G 2P5 (G.C., R.J.W.).
Institute of Biological Chemistry, Washington State University, Pullman, Washington 99164-6340 (S.B., J.B.); andAlberta Innovates Phytola Centre, Department of Agricultural, Food, and Nutritional Science, University of Alberta, Edmonton, Alberta, Canada T6G 2P5 (G.C., R.J.W.)
Plant Physiol. 2015 Apr;167(4):1259-70. doi: 10.1104/pp.114.253641. Epub 2015 Feb 9.
Ricinoleic acid, an industrially useful hydroxy fatty acid (HFA), only accumulates to high levels in the triacylglycerol fraction of castor (Ricinus communis) endosperm, even though it is synthesized on the membrane lipid phosphatidylcholine (PC) from an oleoyl ester. The acyl chains of PC undergo intense remodeling through the process of acyl editing. The identities of the proteins involved in this process, however, are unknown. A phospholipase A2 (PLA2) is thought to be involved in the acyl-editing process. We show here a role for RcsPLA2α in the acyl editing of HFA esterified to PC. RcsPLA2α was identified by its high relative expression in the castor endosperm transcriptome. Coexpression in Arabidopsis (Arabidopsis thaliana) seeds of RcsPLA2α with the castor fatty acid hydroxylase RcFAH12 led to a dramatic decrease in seed HFA content when compared with RcFAH12 expression alone in both PC and the neutral lipid fraction. The low-HFA trait was heritable and gene dosage dependent, with hemizygous lines showing intermediate HFA levels. The low seed HFA levels suggested that RcsPLA2α functions in vivo as a PLA2 with HFA specificity. Activity assays with yeast (Saccharomyces cerevisiae) microsomes showed a high specificity of RcsPLA2α for ricinoleic acid, superior to that of the endogenous Arabidopsis PLA2α. These results point to RcsPLA2α as a phospholipase involved in acyl editing, adapted to specifically removing HFA from membrane lipids in seeds.
蓖麻油酸是一种具有工业用途的羟基脂肪酸（HFA），尽管它是由油酰酯在膜脂磷脂酰胆碱（PC）上合成的，但仅在蓖麻（Ricinus communis）胚乳的三酰甘油部分中积累到高水平。PC的酰基链通过酰基编辑过程经历强烈的重塑。然而，参与这一过程的蛋白质的身份尚不清楚。一种磷脂酶A2（PLA2）被认为参与了酰基编辑过程。我们在此展示了RcsPLA2α在酯化到PC的HFA的酰基编辑中的作用。RcsPLA2α是通过其在蓖麻胚乳转录组中的高相对表达而鉴定出来的。与单独在PC和中性脂质部分中表达蓖麻脂肪酸羟化酶RcFAH12相比，在拟南芥（Arabidopsis thaliana）种子中共同表达RcsPLA2α和RcFAH12导致种子HFA含量显著降低。低HFA性状是可遗传的且依赖基因剂量，半合子品系显示出中等HFA水平。种子中低HFA水平表明RcsPLA2α在体内作为具有HFA特异性的PLA2发挥作用。用酵母（Saccharomyces cerevisiae）微粒体进行的活性测定表明，RcsPLA2α对蓖麻油酸具有高特异性，优于内源性拟南芥PLA2α。这些结果表明RcsPLA2α是一种参与酰基编辑的磷脂酶，适用于从种子中的膜脂中特异性去除HFA。
