PDF(Pubmed)
Abstract：
BACKGROUND: Chemoreception is crucial for insect fitness, underlying for instance food-, host-, and mate finding. Chemicals in the environment are detected by receptors from three divergent gene families: odorant receptors (ORs), gustatory receptors (GRs), and ionotropic receptors (IRs). However, how the chemoreceptor gene families evolve in parallel with ecological specializations remains poorly understood, especially in the order Coleoptera. Hence, we sequenced the genome and annotated the chemoreceptor genes of the specialised ambrosia beetle Trypodendron lineatum (Coleoptera, Curculionidae, Scolytinae) and compared its chemoreceptor gene repertoires with those of other scolytines with different ecological adaptations, as well as a polyphagous cerambycid species.
RESULTS: We identified 67 ORs, 38 GRs, and 44 IRs in T. lineatum (\'Tlin\'). Across gene families, T. lineatum has fewer chemoreceptors compared to related scolytines, the coffee berry borer Hypothenemus hampei and the mountain pine beetle Dendroctonus ponderosae, and clearly fewer receptors than the polyphagous cerambycid Anoplophora glabripennis. The comparatively low number of chemoreceptors is largely explained by the scarcity of large receptor lineage radiations, especially among the bitter taste GRs and the \'divergent\' IRs, and the absence of alternatively spliced GR genes. Only one non-fructose sugar receptor was found, suggesting several sugar receptors have been lost. Also, we found no orthologue in the \'GR215 clade\', which is widely conserved across Coleoptera. Two TlinORs are orthologous to ORs that are functionally conserved across curculionids, responding to 2-phenylethanol (2-PE) and green leaf volatiles (GLVs), respectively.
CONCLUSIONS: Trypodendron lineatum reproduces inside the xylem of decaying conifers where it feeds on its obligate fungal mutualist Phialophoropsis ferruginea. Like previous studies, our results suggest that stenophagy correlates with small chemoreceptor numbers in wood-boring beetles; indeed, the few GRs may be due to its restricted fungal diet. The presence of TlinORs orthologous to those detecting 2-PE and GLVs in other species suggests these compounds are important for T. lineatum. Future functional studies should test this prediction, and chemoreceptor annotations should be conducted on additional ambrosia beetle species to investigate whether few chemoreceptors is a general trait in this specialized group of beetles.
RESULTS: We identified 67 ORs, 38 GRs, and 44 IRs in T. lineatum (\'Tlin\'). Across gene families, T. lineatum has fewer chemoreceptors compared to related scolytines, the coffee berry borer Hypothenemus hampei and the mountain pine beetle Dendroctonus ponderosae, and clearly fewer receptors than the polyphagous cerambycid Anoplophora glabripennis. The comparatively low number of chemoreceptors is largely explained by the scarcity of large receptor lineage radiations, especially among the bitter taste GRs and the \'divergent\' IRs, and the absence of alternatively spliced GR genes. Only one non-fructose sugar receptor was found, suggesting several sugar receptors have been lost. Also, we found no orthologue in the \'GR215 clade\', which is widely conserved across Coleoptera. Two TlinORs are orthologous to ORs that are functionally conserved across curculionids, responding to 2-phenylethanol (2-PE) and green leaf volatiles (GLVs), respectively.
CONCLUSIONS: Trypodendron lineatum reproduces inside the xylem of decaying conifers where it feeds on its obligate fungal mutualist Phialophoropsis ferruginea. Like previous studies, our results suggest that stenophagy correlates with small chemoreceptor numbers in wood-boring beetles; indeed, the few GRs may be due to its restricted fungal diet. The presence of TlinORs orthologous to those detecting 2-PE and GLVs in other species suggests these compounds are important for T. lineatum. Future functional studies should test this prediction, and chemoreceptor annotations should be conducted on additional ambrosia beetle species to investigate whether few chemoreceptors is a general trait in this specialized group of beetles.
摘要：
背景：化学接受对昆虫健康至关重要，例如食物-，主机-,和伴侣发现。环境中的化学物质由三个不同基因家族的受体检测：气味受体（ORs），味觉受体（GR），和离子型受体（IRs）。然而,化学感受器基因家族如何与生态专业化并行进化仍然知之甚少，尤其是鞘翅目。因此，我们对基因组进行了测序，并注释了专门的甲虫Trypodendronlineatum（鞘翅目，孔雀科,Scolytinae）并将其化学感受器基因库与其他具有不同生态适应的scolytines进行了比较，以及多食cerambycid物种。
结果：我们确定了67个ORs，38GR，和在T.lineatum（\'Tlin\'）的44条IRs。在基因家族中，与相关的念珠菌相比，念珠菌的化学感受器较少，咖啡浆果borehypothenemushambei和山松甲虫Dendroctonusponderosae，受体明显少于多食性cerambycid光面斑驳虫。化学感受器的数量相对较低，这在很大程度上可以解释为缺乏大型受体谱系辐射，尤其是在苦味GRS和“不同的IRS”中，以及缺乏选择性剪接的GR基因。只发现了一个非果糖糖受体,表明几个糖受体已经丢失。此外，我们在\“GR215进化枝\”中没有发现直向学，在鞘翅目中广泛保存。两个TlinOR与功能上保守的ORs直系同源，对2-苯基乙醇（2-PE）和绿叶挥发物（GLVs）的反应，分别。
结论：Trypoderonlineum在腐烂的针叶树的木质部内繁殖，以其专性真菌互生的Phialophoropsisferruginea为食。像以前的研究一样，我们的结果表明，在枯木甲虫中，狭窄的吞噬与小的化学感受器数量相关；确实，少数GRs可能是由于其限制的真菌饮食。在其他物种中与检测2-PE和GLV的那些直系同源的TlinOR的存在表明这些化合物对于T.lineatum是重要的。未来的功能研究应该检验这一预测，和化学感受器注释应在其他ambrosia甲虫物种上进行，以研究在这一专门的甲虫组中，化学感受器是否是一般特征。
结果：我们确定了67个ORs，38GR，和在T.lineatum（\'Tlin\'）的44条IRs。在基因家族中，与相关的念珠菌相比，念珠菌的化学感受器较少，咖啡浆果borehypothenemushambei和山松甲虫Dendroctonusponderosae，受体明显少于多食性cerambycid光面斑驳虫。化学感受器的数量相对较低，这在很大程度上可以解释为缺乏大型受体谱系辐射，尤其是在苦味GRS和“不同的IRS”中，以及缺乏选择性剪接的GR基因。只发现了一个非果糖糖受体,表明几个糖受体已经丢失。此外，我们在\“GR215进化枝\”中没有发现直向学，在鞘翅目中广泛保存。两个TlinOR与功能上保守的ORs直系同源，对2-苯基乙醇（2-PE）和绿叶挥发物（GLVs）的反应，分别。
结论：Trypoderonlineum在腐烂的针叶树的木质部内繁殖，以其专性真菌互生的Phialophoropsisferruginea为食。像以前的研究一样，我们的结果表明，在枯木甲虫中，狭窄的吞噬与小的化学感受器数量相关；确实，少数GRs可能是由于其限制的真菌饮食。在其他物种中与检测2-PE和GLV的那些直系同源的TlinOR的存在表明这些化合物对于T.lineatum是重要的。未来的功能研究应该检验这一预测，和化学感受器注释应在其他ambrosia甲虫物种上进行，以研究在这一专门的甲虫组中，化学感受器是否是一般特征。
