Kimberlin Athen N, Han Gongshe, Luttgeharm Kyle D, Chen Ming, Cahoon Rebecca E, Stone Julie M, Markham Jennifer E, Dunn Teresa M, Cahoon Edgar B
Center for Plant Science Innovation and Department of Biochemistry, University of Nebraska-Lincoln, Lincoln, Nebraska 68588 (A.N.K., K.D.L., M.C., R.E.C., J.M.S., J.E.M., E.B.C.); andDepartment of Biochemistry and Molecular Biology, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814 (G.H., T.M.D.).
Center for Plant Science Innovation and Department of Biochemistry, University of Nebraska-Lincoln, Lincoln, Nebraska 68588 (A.N.K., K.D.L., M.C., R.E.C., J.M.S., J.E.M., E.B.C.); andDepartment of Biochemistry and Molecular Biology, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814 (G.H., T.M.D.)
Plant Physiol. 2016 Oct;172(2):889-900. doi: 10.1104/pp.16.00965. Epub 2016 Aug 9.
Sphingolipid synthesis is tightly regulated in eukaryotes. This regulation in plants ensures sufficient sphingolipids to support growth while limiting the accumulation of sphingolipid metabolites that induce programmed cell death. Serine palmitoyltransferase (SPT) catalyzes the first step in sphingolipid biosynthesis and is considered the primary sphingolipid homeostatic regulatory point. In this report, Arabidopsis (Arabidopsis thaliana) putative SPT regulatory proteins, orosomucoid-like proteins AtORM1 and AtORM2, were found to interact physically with Arabidopsis SPT and to suppress SPT activity when coexpressed with Arabidopsis SPT subunits long-chain base1 (LCB1) and LCB2 and the small subunit of SPT in a yeast (Saccharomyces cerevisiae) SPT-deficient mutant. Consistent with a role in SPT suppression, AtORM1 and AtORM2 overexpression lines displayed increased resistance to the programmed cell death-inducing mycotoxin fumonisin B, with an accompanying reduced accumulation of LCBs and C16 fatty acid-containing ceramides relative to wild-type plants. Conversely, RNA interference (RNAi) suppression lines of AtORM1 and AtORM2 displayed increased sensitivity to fumonisin B and an accompanying strong increase in LCBs and C16 fatty acid-containing ceramides relative to wild-type plants. Overexpression lines also were found to have reduced activity of the class I ceramide synthase that uses C16 fatty acid acyl-coenzyme A and dihydroxy LCB substrates but increased activity of class II ceramide synthases that use very-long-chain fatty acyl-coenzyme A and trihydroxy LCB substrates. RNAi suppression lines, in contrast, displayed increased class I ceramide synthase activity but reduced class II ceramide synthase activity. These findings indicate that ORM mediation of SPT activity differentially regulates functionally distinct ceramide synthase activities as part of a broader sphingolipid homeostatic regulatory network.
鞘脂合成在真核生物中受到严格调控。植物中的这种调控确保有足够的鞘脂来支持生长，同时限制诱导程序性细胞死亡的鞘脂代谢物的积累。丝氨酸棕榈酰转移酶（SPT）催化鞘脂生物合成的第一步，被认为是鞘脂稳态调节的主要控制点。在本报告中，发现拟南芥（Arabidopsis thaliana）假定的SPT调节蛋白，类orosomucoid蛋白AtORM1和AtORM2，与拟南芥SPT发生物理相互作用，并在酵母（Saccharomyces cerevisiae）SPT缺陷型突变体中与拟南芥SPT亚基长链碱1（LCB1）和LCB2以及SPT的小亚基共表达时抑制SPT活性。与在抑制SPT中的作用一致，AtORM1和AtORM2过表达系对诱导程序性细胞死亡的霉菌毒素伏马菌素B表现出增强的抗性，相对于野生型植物，伴随的LCB和含C16脂肪酸的神经酰胺积累减少。相反，AtORM1和AtORM2的RNA干扰（RNAi）抑制系对伏马菌素B表现出增强的敏感性，相对于野生型植物，伴随的LCB和含C16脂肪酸的神经酰胺强烈增加。还发现过表达系使用C16脂肪酸酰基辅酶A和二羟基LCB底物的I类神经酰胺合酶活性降低，但使用超长链脂肪酸酰基辅酶A和三羟基LCB底物的II类神经酰胺合酶活性增加。相比之下，RNAi抑制系表现出I类神经酰胺合酶活性增加，但II类神经酰胺合酶活性降低。这些发现表明，作为更广泛的鞘脂稳态调节网络的一部分，ORM对SPT活性的介导差异调节功能不同的神经酰胺合酶活性。
