Yilamujiang Ayufu, Reichelt Michael, Mithöfer Axel
Department of Bioorganic Chemistry.
Department of Biochemistry, Max Planck Institute for Chemical Ecology, Hans-Knöll-Str. 8, 07745 Jena, Germany.
Ann Bot. 2016 Aug;118(2):369-75. doi: 10.1093/aob/mcw110. Epub 2016 Jun 20.
Carnivorous Nepenthes plants use modified leaves forming pitfall traps to capture and digest prey, mainly insects, for additional nutrient supply. These traps, so called pitchers, contain a plant-derived fluid composed of many hydrolytic enzymes and defence-related proteins. In this study, the prey-induced induction of corresponding genes of those proteins and a role for phytohormones in this process was analysed.
Tissue from insect prey-fed, chitin- and phytohormone-challenged pitchers was harvested and analysed for selected gene expressions by a quantitative PCR technique. Phytohormone levels were determined by LC-MS/MS. Nepenthesin proteolytic activities were measured in the digestive fluid using a fluorescence substrate.
Insect prey in the pitchers induced the accumulation of phytohormones such as jasmonates as well as the transcription of studied genes encoding a chitinase 3 and a protease (nepenthesin I), whereas a defence-related protein (PR-1) gene was not induced. Treatment with chitin as a component of the insects' exoskeleton triggered the accumulation of jasmonates, the expression of nepenthesin I and chitinase 3 genes similar to jasmonic acid treatment, and induced protease activity in the fluid. All detectable responses were slowly induced.
The results suggest that upon insect prey catch a sequence of signals is initiated: (1) insect-derived chitin, (2) jasmonate as endogenous phytohormone signal, (3) the induction of digestive gene expression and (4) protein expression. This resembles a similar hierarchy of events as described from plant pathogen/herbivore interactions, supporting the idea that carnivory evolved from plant defences.
肉食性猪笼草属植物利用特化的叶子形成捕虫笼来捕获和消化猎物（主要是昆虫），以获取额外的营养供应。这些捕虫笼，即所谓的捕虫瓶，含有一种由多种水解酶和防御相关蛋白组成的植物源液体。在本研究中，分析了猎物诱导的这些蛋白质相应基因的表达以及植物激素在此过程中的作用。
采集喂食昆虫猎物、用几丁质和植物激素处理的捕虫瓶组织，通过定量PCR技术分析选定基因的表达。采用LC-MS/MS测定植物激素水平。使用荧光底物测定消化液中的猪笼草蛋白酶活性。
捕虫瓶中的昆虫猎物诱导了茉莉酸等植物激素的积累以及编码几丁质酶3和一种蛋白酶（猪笼草蛋白酶I）的研究基因的转录，而一个防御相关蛋白（PR-1）基因未被诱导。用几丁质作为昆虫外骨骼的成分进行处理引发了茉莉酸的积累、猪笼草蛋白酶I和几丁质酶3基因的表达，类似于茉莉酸处理，并诱导了消化液中的蛋白酶活性。所有可检测到的反应诱导缓慢。
结果表明，捕获昆虫猎物后会启动一系列信号：（1）昆虫来源的几丁质，（2）茉莉酸作为内源性植物激素信号，（3）消化基因表达的诱导，（4）蛋白质表达。这类似于植物病原体/食草动物相互作用中描述的类似事件层次结构，支持了肉食性从植物防御进化而来的观点。
