Data from: The transcriptome response of Heliconius melpomene larvae to a novel host plant

In the warfare between herbivore and host plant, insects have evolved a variety of defensive mechanisms, including allelochemical transformation and excretion. Several studies have explored the transcriptome responses of insects after host plant shifts in order to understand these mechanisms. We investigated the plastic responses of H. melpomene larvae feeding on a native host Passiflora menispermifolia and a less strongly defended non-host species, P. biflora. In total 326 differentially expressed genes were identified, with a greater number upregulated on the more strongly defended native host. Functional annotation showed that detoxifying enzymes, transporters and components of peritrophic membrane were strongly represented. In total, 30 candidate detoxification genes were differentially expressed, with glutathione S-transferases (GSTs) and UDP-glucuronosyltransferases showing the highest proportion of differential expression, 27.3% and 17.3%, respectively. These differentially-expressed detoxification genes were shown to evolve mainly under the influence of purifying selection, suggesting that protein-coding evolution has not played a major role in host adaptation. We found only one gene, GSTe3, with evidence of adaptive evolution at H40, which is around the G-site and might alter enzyme activity. Based on our transcriptome and molecular evolution analysis, we suggest that transcriptional plasticity of genes in a herbivore may play an important role in adaptation to a new host plant.在植食性昆虫与宿主植物的协同进化攻防过程中，昆虫已演化出多种防御机制，包括他感化学物（allelochemical）转化与排泄作用。为解析此类防御机制，已有多项研究围绕宿主植物转换后昆虫的转录组响应展开探索。本研究针对取食本土宿主植物*Passiflora menispermifolia*以及防御能力较弱的非宿主物种*P. biflora*的*H. melpomene*幼虫的表型可塑性响应开展了探究。最终共鉴定出326个差异表达基因（differentially expressed genes, DEGs），其中在防御能力更强的本土宿主植物上取食的幼虫体内，上调表达的基因数量更多。功能注释结果显示，解毒酶、转运蛋白以及围食膜（peritrophic membrane）组分在差异表达基因中显著富集。本研究共筛选出30个差异表达的候选解毒基因，其中谷胱甘肽S-转移酶（glutathione S-transferases, GSTs）与尿苷二磷酸葡萄糖醛酸转移酶（UDP-glucuronosyltransferases）的差异表达占比最高，分别为27.3%与17.3%。此类差异表达的解毒基因主要处于纯化选择（purifying selection）的演化压力之下，表明蛋白质编码序列的演化并未在宿主适应性过程中发挥主要作用。本研究仅发现GSTe3这一个基因，其H40位点存在适应性演化信号——该位点位于G结合位点附近，可能会改变酶的催化活性。综合转录组与分子演化分析结果，本研究认为植食性昆虫体内基因的转录可塑性在宿主植物适应性转换过程中发挥着关键作用。