Tropical Biosphere Research Center, University of the Ryukyus, Okinawa, 903-0213, Japan.
NIBB Core Research Facilities, National Institute for Basic Biology, Okazaki, 444-8585, Japan.
Insect Biochem Mol Biol. 2019 Aug;111:103177. doi: 10.1016/j.ibmb.2019.103177. Epub 2019 Jun 20.
In the evolutionarily-derived termite subfamily Nasutitermitinae (family Termitidae), soldiers defend their nestmates by discharging polycyclic diterpenes from a head projection called the "nasus." The diterpenes are synthesised in the frontal gland from the precursor geranylgeranyl diphosphate (GGPP), which is generally used for post-translational modification of proteins in animals. In this study, we constructed a comprehensive gene catalogue to search for genes involved in the diterpene biosynthesis by assembling RNA sequencing reads of Nasutitermes takasagoensis, identifying eight gene copies for GGPP synthase (GGPPS). The number of gene copies is much larger in contrast to other related insects. Gene cloning by reverse transcription-PCR and rapid amplification of cDNA ends confirmed that seven GGPPS genes (NtGGPPS1 to NtGGPPS7) have highly variable untranslated regions. Molecular phylogenetic analysis showed that the NtGGPPS7 gene was grouped with homologs obtained from ancestral termites that have only a single copy of the gene, and the NtGGPPS6 gene was grouped with homologs obtained from a basal lineage of termitids, in which soldiers do not synthesise diterpenes. As the sister group to this clade, furthermore, a monophyletic clade included all the other NtGGPPS genes (NtGGPPS1 to NtGGPPS5). Expression analyses revealed that NtGGPPS7 gene was expressed in all the examined castes and tissues, whereas all the other genes were expressed only in the soldier head. These results suggest that gene duplication followed by subfunctionalisation of the GGPPS genes might have accompanied the evolution of chemical defence in the nasute termite lineage.
在进化衍生的白蚁亚科（白蚁科）中，兵蚁通过从头部突起“鼻”中排出多环二萜来保护其巢友。这些二萜是由前体香叶基香叶基二磷酸（GGPP）在前额腺中合成的，GGPP 通常用于动物蛋白质的翻译后修饰。在这项研究中，我们通过组装黄胸散白蚁的 RNA 测序读数构建了一个综合基因目录，以搜索涉及二萜生物合成的基因，确定了 8 个 GGPP 合酶（GGPPS）基因拷贝。与其他相关昆虫相比，基因拷贝数要大得多。通过反转录 PCR 和 cDNA 末端快速扩增克隆基因证实，7 个 GGPPS 基因（NtGGPPS1 至 NtGGPPS7）具有高度可变的非翻译区。分子系统发育分析表明，NtGGPPS7 基因与从具有单拷贝基因的原始白蚁中获得的同源物聚类，而 NtGGPPS6 基因与从不合成二萜的白蚁科的基础谱系中获得的同源物聚类。此外，作为这个分支的姐妹群，一个单系群包括所有其他 NtGGPPS 基因（NtGGPPS1 至 NtGGPPS5）。表达分析表明，NtGGPPS7 基因在所有检查的巢群和组织中表达，而所有其他基因仅在兵蚁头部表达。这些结果表明，GGPPS 基因的复制和亚功能化可能伴随着化学防御在鼻白蚁谱系中的进化。
