Salazar-Jaramillo Laura, Jalvingh Kirsten M, de Haan Ammerins, Kraaijeveld Ken, Buermans Henk, Wertheim Bregje
Groningen Institute for Evolutionary Life Sciences, University of Groningen, Nijenborgh 7, Groningen, 9700 CC, The Netherlands.
Institute of Evolutionary Biology, The University of Edinburgh, Charlotte Auerbach Road, Edinburgh, EH9 3FL, UK.
BMC Genomics. 2017 Apr 27;18(1):331. doi: 10.1186/s12864-017-3697-3.
Parasitoid resistance in Drosophila varies considerably, among and within species. An immune response, lamellocyte-mediated encapsulation, evolved in a subclade of Drosophila and was subsequently lost in at least one species within this subclade. While the mechanisms of resistance are fairly well documented in D. melanogaster, much less is known for closely related species. Here, we studied the inter- and intra-species variation in gene expression after parasitoid attack in Drosophila. We used RNA-seq after parasitization of four closely related Drosophila species of the melanogaster subgroup and replicated lines of D. melanogaster experimentally selected for increased resistance to gain insights into short- and long-term evolutionary changes.
We found a core set of genes that are consistently up-regulated after parasitoid attack in the species and lines tested, regardless of their level of resistance. Another set of genes showed no up-regulation or expression in D. sechellia, the species unable to raise an immune response against parasitoids. This set consists largely of genes that are lineage-restricted to the melanogaster subgroup. Artificially selected lines did not show significant differences in gene expression with respect to non-selected lines in their responses to parasitoid attack, but several genes showed differential exon usage.
We showed substantial similarities, but also notable differences, in the transcriptional responses to parasitoid attack among four closely related Drosophila species. In contrast, within D. melanogaster, the responses were remarkably similar. We confirmed that in the short-term, selection does not act on a pre-activation of the immune response. Instead it may target alternative mechanisms such as differential exon usage. In the long-term, we found support for the hypothesis that the ability to immunologically resist parasitoid attack is contingent on new genes that are restricted to the melanogaster subgroup.
果蝇对寄生蜂的抗性在物种间和物种内差异很大。一种免疫反应，即由片状血细胞介导的包囊化反应，在果蝇的一个亚分支中进化而来，随后在该亚分支中的至少一个物种中消失。虽然在黑腹果蝇中抗性机制已有相当充分的记录，但对于其近缘物种却知之甚少。在这里，我们研究了果蝇在遭受寄生蜂攻击后基因表达的种间和种内差异。我们在对黑腹果蝇亚组的四个近缘果蝇物种进行寄生后使用RNA测序，并对经过实验选择以增强抗性的黑腹果蝇品系进行了重复实验，以深入了解短期和长期的进化变化。
我们发现了一组核心基因，在所测试的物种和品系中，无论其抗性水平如何，在遭受寄生蜂攻击后这些基因都会持续上调。另一组基因在无法对寄生蜂产生免疫反应的塞舌尔果蝇中没有上调或表达。这组基因主要由仅限于黑腹果蝇亚组的谱系特异性基因组成。人工选择的品系在对寄生蜂攻击的反应中，与未选择的品系相比，基因表达没有显著差异，但有几个基因表现出不同的外显子使用情况。
我们发现四个近缘果蝇物种在对寄生蜂攻击的转录反应中存在大量相似之处，但也有显著差异。相比之下，在黑腹果蝇内部，反应非常相似。我们证实，在短期内，选择并不作用于免疫反应的预激活。相反，它可能针对诸如不同外显子使用等替代机制。从长期来看，我们发现支持这样一种假设，即免疫抵抗寄生蜂攻击的能力取决于仅限于黑腹果蝇亚组的新基因。
