First, fourth, seventh, eighth, and ninth: College of Life Science, Hebei Agricultural University, Baoding, Hebei 071001, China; first, fourth, and ninth authors: Key Laboratory of Hebei Province for Plant Physiology and Molecular Pathology, Hebei Agricultural University, Baoding, Hebei 071001, China; and second, third, fifth, and sixth authors: Research Center of Chinese Jujube, Hebei Agricultural University, Baoding, Hebei 071001, China.
Phytopathology. 2018 Sep;108(9):1067-1077. doi: 10.1094/PHYTO-02-18-0058-R. Epub 2018 Jul 13.
Phytoplasmas parasitize plant phloem tissue and cause many economically important plant diseases. Jujube witches'-broom disease is a destructive phytoplasma disease of Chinese jujube (Ziziphus jujuba). To elucidate the influence of phytoplasma on host photosynthetic, carbohydrate and energy metabolisms, four types of jujube tissues showing disease symptoms with different severity were investigated at the structural, physiological, and molecular levels. Quantitative real-time PCR and high-performance liquid chromatography results showed that the down-regulation of genes related to photosynthesis and the lower contents of chlorophyll in diseased leaves. This clearly inhibited the light-harvesting and photosystem II activity of photosynthesis; however, overexpression of genes related to starch, sucrose and glucose synthesis led to higher contents of these carbohydrates. Meanwhile, transmission electron microscopy images revealed that dense amounts of phytoplasmas accumulated in the sieve elements of diseased petiole phloem, and the structure of the grana and stroma lamellae of chloroplasts in the diseased leaves was destroyed. Phytoplasma infection inhibited photosynthesis and led to abnormal carbohydrate accumulation in the diseased leaves. Furthermore, comparative metabolite analysis indicated that phytoplasma infection also stimulated amino acids and energy metabolisms of the diseased leaves. Continually inhibiting the photosynthetic process and stimulating carbohydrate and energy metabolisms of diseased trees may exhaust their nutrients. Our results highlight the importance of changing host metabolisms during the pathogenic process.
植原体寄生在植物韧皮部组织中，引起许多重要的植物病害。枣树丛枝病是中国枣树（Ziziphus jujuba）的一种破坏性植原体病害。为了阐明植原体对寄主光合作用、碳水化合物和能量代谢的影响，我们在结构、生理和分子水平上研究了四种表现出不同严重程度病害症状的枣树组织。定量实时 PCR 和高效液相色谱结果表明，与光合作用相关的基因下调，病叶中的叶绿素含量降低。这明显抑制了光合作用的光捕获和光系统 II 活性；然而，与淀粉、蔗糖和葡萄糖合成相关的基因的过度表达导致这些碳水化合物含量升高。同时，透射电子显微镜图像显示，大量植原体在患病叶柄韧皮部筛管中积累，患病叶片叶绿体的基粒和基质片层结构被破坏。植原体感染抑制了光合作用，导致病叶中碳水化合物的异常积累。此外，比较代谢物分析表明，植原体感染还刺激了病叶中的氨基酸和能量代谢。持续抑制病树的光合作用和刺激碳水化合物和能量代谢可能会耗尽它们的营养物质。我们的研究结果强调了在致病过程中改变寄主代谢的重要性。
