Predicted Effector Molecules in the Salivary Secretome of the Pea Aphid (<i>Acyrthosiphon pisum</i>): A Dual Transcriptomic/Proteomic Approach

The relationship between aphids and their host plants is thought to be functionally analogous to plant−pathogen interactions. Although virulence effector proteins that mediate plant defenses are well-characterized for pathogens such as bacteria, oomycetes, and nematodes, equivalent molecules in aphids and other phloem-feeders are poorly understood. A dual transcriptomic−proteomic approach was adopted to generate a catalog of candidate effector proteins from the salivary glands of the pea aphid, Acyrthosiphon pisum. Of the 1557 transcript supported and 925 mass spectrometry identified proteins, over 300 proteins were identified with secretion signals, including proteins that had previously been identified directly from the secreted saliva. Almost half of the identified proteins have no homologue outside aphids and are of unknown function. Many of the genes encoding the putative effector proteins appear to be evolving at a faster rate than homologues in other insects, and there is strong evidence that genes with multiple copies in the genome are under positive selection. Many of the candidate aphid effector proteins were previously characterized in typical phytopathogenic organisms (e.g., nematodes and fungi) and our results highlight remarkable similarities in the saliva from plant-feeding nematodes and aphids that may indicate the evolution of common solutions to the plant−parasitic lifestyle.蚜虫与其寄主植物间的相互作用，在功能上被认为与植物-病原体互作高度相似。尽管细菌、卵菌及线虫等植物病原体内介导宿主防御反应的毒力效应蛋白已得到充分解析，但蚜虫与其他韧皮部取食昆虫中的等效效应分子却鲜有研究。本研究采用转录组-蛋白质组双组学方法，从豌豆蚜（Acyrthosiphon pisum）的唾液腺中构建了候选效应蛋白目录。在1557个经转录本验证、925个经质谱鉴定的蛋白中，共鉴定出300余种带有分泌信号的蛋白，其中包含此前直接从分泌唾液中检出的蛋白。近半数鉴定得到的蛋白在蚜虫类群外无同源序列，功能尚不明确。多数编码推定效应蛋白的基因，其进化速率显著快于其他昆虫的同源基因；同时有充分证据表明，基因组内存在多拷贝的此类基因受到正选择作用。本研究鉴定的候选蚜虫效应蛋白中，诸多蛋白此前已在典型植物病原生物（如线虫与真菌）中得到表征；我们的研究结果揭示，植食性线虫与蚜虫的唾液存在显著相似性，这或暗示二者演化出了应对植物寄生生活方式的共通策略。