Odorant and Gustatory Receptors in the Tsetse Fly Glossina morsitans morsitans

Tsetse flies use olfactory and gustatory responses, through odorant and gustatory receptors (ORs and GRs), to interact with their environment. Glossina morsitans morsitans genome ORs and GRs were annotated using homologs of these genes in Drosophila melanogaster and an ab initio approach based on OR and GR specific motifs in G. m. morsitans gene models coupled to gene ontology (GO). Phylogenetic relationships among the ORs or GRs and the homologs were determined using Maximum Likelihood estimates. Relative expression levels among the G. m. morsitans ORs or GRs were established using RNA-seq data derived from adult female fly. Overall, 46 and 14 putative G. m. morsitans ORs and GRs respectively were recovered. These were reduced by 12 and 59 ORs and GRs respectively compared to D. melanogaster. Six of the ORs were homologous to a single D. melanogaster OR (DmOr67d) associated with mating deterrence in females. Sweet taste GRs, present in all the other Diptera, were not recovered in G. m. morsitans. The GRs associated with detection of CO2 were conserved in G. m. morsitans relative to D. melanogaster. RNA-sequence data analysis revealed expression of GmmOR15 locus represented over 90% of expression profiles for the ORs. The G. m. morsitans ORs or GRs were phylogenetically closer to those in D. melanogaster than to other insects assessed. We found the chemoreceptor repertoire in G. m. morsitans smaller than other Diptera, and we postulate that this may be related to the restricted diet of blood-meal for both sexes of tsetse flies. However, the clade of some specific receptors has been expanded, indicative of their potential importance in chemoreception in the tsetse.

采采蝇通过嗅觉受体（Odorant Receptors，ORs）与味觉受体（Gustatory Receptors，GRs）介导的嗅觉与味觉响应，与外界环境实现信息交互。本研究以黑腹果蝇（Drosophila melanogaster）中上述基因的同源序列为参照，结合基于刺舌蝇指名亚种（Glossina morsitans morsitans）基因模型中OR与GR特异性基序、并耦合基因本体（Gene Ontology，GO）注释的从头预测方法，对该亚种基因组中的OR与GR进行了注释。利用最大似然法构建系统发育树，以明确OR、GR及其同源基因之间的系统发育关系。基于成年雌蝇的RNA测序（RNA-seq）数据，明确了刺舌蝇指名亚种OR与GR的相对表达水平。最终共鉴定得到46个推定的刺舌蝇指名亚种OR以及14个推定的GR。相较于黑腹果蝇，该亚种的OR与GR基因数目分别减少了12个和59个。其中6个OR与黑腹果蝇中单一的DmOr67d同源，该受体与雌蝇的交配阻遏行为相关。在其他所有双翅目昆虫中均存在的甜味味觉受体，并未在刺舌蝇指名亚种中被鉴定到。相较于黑腹果蝇，刺舌蝇指名亚种中与二氧化碳检测相关的GR基因仍保持保守。RNA测序数据分析显示，GmmOR15基因座的表达量占该亚种所有OR总表达量的90%以上。相较于其他受试昆虫，刺舌蝇指名亚种的OR与GR在系统发育上与黑腹果蝇的亲缘关系更近。本研究发现刺舌蝇指名亚种的化学受体组相较于其他双翅目昆虫更为精简，我们推测这可能与采采蝇雌雄两性均仅以血液为食的限制性饮食模式有关。但部分特定受体的进化分支发生了扩增，这提示它们在采采蝇的化学感受过程中可能具有重要作用。