Unité Propre de Recherche 2357, Centre National de la Recherche Scientifique, Institut de Biologie Moléculaire des Plantes, conventionné avec l'Université de Strasbourg, F-67083 Strasbourg, France.
Plant Physiol. 2014 Feb;164(2):935-50. doi: 10.1104/pp.113.232546. Epub 2013 Dec 23.
S-Carvone has been described as a negative regulator of mevalonic acid (MVA) production by interfering with 3-hydroxy-3-methyl glutaryl coenzyme A reductase (HMGR) activity, a key player in isoprenoid biosynthesis. The impact of this monoterpene on the production of capsidiol in Nicotiana tabacum, an assumed MVA-derived sesquiterpenoid phytoalexin produced in response to elicitation by cellulase, was investigated. As expected, capsidiol production, as well as early stages of elicitation such as hydrogen peroxide production or stimulation of 5-epi-aristolochene synthase activity, were repressed. Despite the lack of capsidiol synthesis, apparent HMGR activity was boosted. Feeding experiments using (1-13C)Glc followed by analysis of labeling patterns by 13C-NMR, confirmed an MVA-dependent biosynthesis; however, treatments with fosmidomycin, an inhibitor of the MVA-independent 2-C-methyl-D-erythritol 4-phosphate (MEP) isoprenoid pathway, unexpectedly down-regulated the biosynthesis of this sesquiterpene as well. We postulated that S-carvone does not directly inhibit the production of MVA by inactivating HMGR, but possibly targets an MEP-derived isoprenoid involved in the early steps of the elicitation process. A new model is proposed in which the monoterpene blocks an MEP pathway-dependent protein geranylgeranylation necessary for the signaling cascade. The production of capsidiol was inhibited when plants were treated with some inhibitors of protein prenylation or by further monoterpenes. Moreover, S-carvone hindered isoprenylation of a prenylable GFP indicator protein expressed in N. tabacum cell lines, which can be chemically complemented with geranylgeraniol. The model was further validated using N. tabacum cell extracts or recombinant N. tabacum protein prenyltransferases expressed in Escherichia coli. Our study endorsed a reevaluation of the effect of S-carvone on plant isoprenoid metabolism.
S-香芹酮被描述为通过干扰 3-羟基-3-甲基戊二酰辅酶 A 还原酶 (HMGR) 活性来抑制甲羟戊酸 (MVA) 产生的负调节剂，HMGR 是异戊烯基生物合成的关键酶。本研究调查了单萜 S-香芹酮对烟草中贝壳杉烯醇产生的影响，贝壳杉烯醇是一种假定的 MVA 衍生的倍半萜类植物抗毒素，可响应纤维素酶的诱导产生。正如预期的那样，贝壳杉烯醇的产生以及诱导的早期阶段，如过氧化氢的产生或 5-表豆甾烯合酶活性的刺激，都受到了抑制。尽管缺乏贝壳杉烯醇的合成，但明显的 HMGR 活性得到了增强。通过用（1-13C）Glc 进行喂养实验，然后通过 13C-NMR 分析标记模式，证实了 MVA 依赖性生物合成；然而，用 fosmidomycin（一种 MVA 非依赖性 2-C-甲基-D-赤藓醇 4-磷酸 (MEP) 异戊烯基途径的抑制剂）处理出乎意料地也下调了该倍半萜的生物合成。我们推测 S-香芹酮不是通过使 HMGR 失活来直接抑制 MVA 的产生，而是可能靶向参与诱导过程早期步骤的 MEP 衍生的异戊烯基。提出了一个新的模型，其中单萜阻断了信号级联中必需的 MEP 途径依赖性蛋白香叶基香叶基化。当用一些蛋白异戊烯基化抑制剂或其他单萜处理植物时，贝壳杉烯醇的产生受到抑制。此外，S-香芹酮阻碍了在烟草细胞系中表达的可异戊烯基化 GFP 指示剂蛋白的异戊烯基化，该蛋白可以用香叶基香叶醇进行化学互补。该模型还使用烟草细胞提取物或在大肠杆菌中表达的重组烟草蛋白异戊烯基转移酶进行了验证。我们的研究支持了对 S-香芹酮对植物异戊烯代谢影响的重新评估。
