Downy mildew is a serious disease in cucumber production worldwide, which is caused by Pseudoperonospora cubensis (Berk. & Curt.) Rostov. Underlying the mechanism of cucumber response to downy mildew infection is important for breeding improvement and production; however, the research remains largely elusive. A comparative proteomic approach was used to reveal the differential accumulation of the proteomes from leaves of cucumber (susceptible line and resistant line) that were inoculated with P. cubensis or not by two-dimensional electrophoresis and MALDI-TOF/TOF MS. A total of 76 protein spots were successfully identified with significant changes in abundance (> 2-fold, P < 0.05) in downy mildew infected or not leaves for the susceptible line and resistant line. By the functional annotation, these proteins were classified into 8 groups including photosynthesis (29%), energy and metabolism (29%), cell rescue and defense (17%), and protein biosynthesis, folding and degradation (13%), unclassified (7%), nucleotide metabolism (3%), signal transduction (1%) and cellular process (1%). Among the 17 differentially expressed proteins between the resistant and susceptible cucumber line, most of the protein spots were concentrated in cell rescue and defense (4) and energy and metabolism (4). Moreover, a schematic diagram containing majority of the metabolic pathways of cucumber leaves in response to downy mildew was proposed. This network revealed the positive effect of several functional components in cucumber seedlings' resistant to downy mildew such as accumulation of energy supply and resistance-related proteins, hastened protein metabolism and photorespiratory, inhibited photosynthesis, and triggered photosystem repair and programmed cell death. Taken together, these results have advanced a further understanding of the key metabolic pathways of cucumber resistance to downy mildew and pathogen control in the proteomic level.

霜霉病是世界范围内黄瓜生产中的一种严重病害，由Pseudoperonospora cubensis (Berk. & Curt.) Rostov 引起。黄瓜对霜霉病感染的反应机制对于育种改良和生产很重要；然而，这项研究在很大程度上仍然难以捉摸。比较蛋白质组学方法用于通过二维电泳和 MALDI-TOF/TOF MS 揭示黄瓜叶（易感品系和抗性品系）中蛋白质组的差异积累，这些黄瓜叶接种或未接种 P.cubensis。共成功鉴定了 76 个蛋白质点，其丰度变化显着（> 2 倍，P< 0.05) 在霜霉病感染或未感染叶为易感品系和抗病品系。根据功能注释，这些蛋白质被分为光合作用（29%）、能量与代谢（29%）、细胞拯救与防御（17%）和蛋白质生物合成、折叠和降解（13%）8类，未分类（ 7%)、核苷酸代谢 (3%)、信号转导 (1%) 和细胞过程 (1%)。在抗性和易感黄瓜品系之间的 17 个差异表达蛋白中，大部分蛋白点集中在细胞拯救和防御 (4) 和能量和代谢 (4) 中。此外，还提出了包含黄瓜叶片响应霜霉病的大部分代谢途径的示意图。该网络揭示了黄瓜幼苗抗霜霉病的几种功能成分的积极作用，例如能量供应和抗性相关蛋白质的积累，加速蛋白质代谢和光呼吸，抑制光合作用，触发光系统修复和程序性细胞死亡。总之，这些结果促进了对蛋白质组水平上黄瓜抗霜霉病和病原体控制的关键代谢途径的进一步理解。