Data from: Effect of host plant and immune challenge on the levels of chemosensory and odorant-binding proteins in caterpillar salivary glands

More than half of the proteome from mandibular glands in caterpillars is represented by chemosensory proteins. Based on sequence similarity, these proteins are putative transporters of ligands to gustatory receptors in sensory organs of insects. We sought to determine whether these proteins are inducible by comparing, both qualitatively and quantitatively, the salivary (mandibular and labial) proteomes from caterpillars (Vanessa cardui) reared on different plants and artificial diet containing either bacteria or bacterial cell-walls. We included a treatment where the caterpillars were switched from feeding on artificial diet to plant material at some point in their development. Additionally, we evaluated the degree of overlap between the proteomes in the hemolymph-filled coelom and salivary glands of caterpillars reared on plant material. We found that the quality and quantity of the identified proteins differed clearly between hemolymph-filled coelom, labial and mandibular glands. Our results indicated that even after molting and two-day feeding on a new diet, protein production is affected by the previous food source used by the caterpillar. Candidate proteins involved in chemosensory perception by insects were detected: three chemosensory (CSPs) and two odorant-binding proteins (OBPs). Using the relative amounts of these proteins across tissues and treatments as criteria for their classification, we detected hemolymph- and mandibular gland-specific CSPs and observed that their levels were affected by caterpillar diet. Moreover, we could compare the protein and transcript levels across tissues and treatment for at least one CSP and one OBP. Therefore, we have identified specific isoforms for testing the role of CSPs and OBPs in plant and pathogen recognition. We detected catalase, immune-related protein and serine proteases and their inhibitors in high relative levels in the mandibular glands in comparison to the labial glands. These findings suggest that the mandibular glands of caterpillars may play an important role protecting the caterpillar from oxidative stress, pathogens and aiding in digestion. Contamination with hemolymph proteins during dissection of salivary glands from caterpillars may occur but it is not substantial since the proteomes from hemolymph, mandibular and labial glands were easily discriminated from each other by principal component analysis of proteomic data.

毛虫下颚腺的蛋白质组（proteome）中，超过一半的组分为化学感受蛋白（chemosensory proteins）。基于序列同源性，这类蛋白被推测为昆虫感觉器官内味觉受体（gustatory receptors）的配体转运蛋白。本研究通过定性与定量比较取食不同植物、以及取食含细菌或细菌细胞壁的人工饲料的大红蛱蝶（Vanessa cardui）幼虫的唾液（下颚腺与下唇腺）蛋白质组（salivary proteomes），旨在探究这类蛋白是否可被诱导表达。此外，我们设置了一组处理组：在幼虫发育的特定阶段将其从人工饲料转移至植物材料上取食。同时，我们还评估了取食植物饲料的幼虫的充满血淋巴的体腔（hemolymph-filled coelom）与唾液腺的蛋白质组重叠程度。研究发现，充满血淋巴的体腔、下唇腺与下颚腺中鉴定出的蛋白在种类与含量上均存在显著差异。结果表明，即使幼虫完成蜕皮并在新饲料上取食两天，其蛋白合成仍会受到先前食物来源的影响。我们检测到了参与昆虫化学感受的候选蛋白：3种化学感受蛋白（CSPs）与2种气味结合蛋白（odorant-binding proteins, OBPs）。以这些蛋白在不同组织与处理组中的相对含量作为分类依据，我们发现了血淋巴特异性与下颚腺特异性的CSPs，并观察到其表达水平受幼虫饲料的调控。此外，我们可针对至少一种CSP与一种OBP，比较其在不同组织与处理组中的蛋白与转录水平（transcript levels）。据此，我们已鉴定出特异性同工型（isoforms），可用于验证CSPs与OBPs在植物与病原体识别过程中的功能。与下唇腺相比，下颚腺中过氧化氢酶（catalase）、免疫相关蛋白、丝氨酸蛋白酶（serine proteases）及其抑制剂的相对含量显著更高。上述发现表明，毛虫的下颚腺可能在抵御氧化应激与病原体侵害，以及辅助消化过程中发挥重要作用。在解剖毛虫唾液腺的过程中可能存在血淋巴蛋白污染，但该污染程度较低，因为通过蛋白质组数据的主成分分析（Principal Component Analysis, PCA）可轻松区分血淋巴、下颚腺与下唇腺的蛋白质组。