Evolution of Soldier-Specific Venomous Protease in Social Aphids
Evolution of Soldier-Specific Venomous Protease in Social Aphids
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DOI：
10.1093/molbev/msn203
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发表时间：
2008-12-01
影响因子：
10.7
通讯作者：
Fukatsu, Takema
中科院分区：
文献类型：
--
作者：
Kutsukake, Mayako;Nikoh, Naruo;Fukatsu, Takema
在蚜虫属的社会蚜虫中，组织蛋白酶B家族的半胱氨酸蛋白酶基因表现出细菌特异性表达和肠蛋白酶产生。该产品经口服排泄，由士兵注射到天敌体内，从而发挥杀虫活性。在试图深入了解新的有毒蛋白酶的利他种姓已经演变，我们调查了特定类型（S型）和非特异性型（N型）组织蛋白酶B基因从社会和非社会蚜虫。所有的社会蚜虫检查，代表属蚜虫，Astegopteryx，角蚜，具有S型和N型基因。系统发育上远缘的非社会性蚜虫也具有与S型和N型同源的组织蛋白酶B基因，表明这些基因在现存蚜虫的共同祖先中的进化起源。在蚜虫中，S型基因表现出明显的寄主特异性表达，加速了分子进化，而N型基因则没有。在Astegopteryx和Cerataphis物种中，S-型和N-型基因均未表现出明显的生物特异性表达，也未加速分子进化。这些结果表明，S型基因在蚜虫属分化后获得了毒特异性表达和毒功能。在S型蛋白酶的结构模型中，加速的分子进化与分子表面而不是催化裂缝有关，这表明毒蛋白的活性可能是通过对分子表面进行相对较小的修饰而不是通过产生新的活性位点获得的。在Cerataphis jamuritsu的S-型基因，虽然含有一个终止密码子，结构上几乎完整，仍然转录，这表明最近的基因拷贝的伪基因化和可能的相关性放松功能的限制，在高度倍增的蛋白酶基因家族。根据这些结果，我们认为，在蚜虫组织蛋白酶B基因的大规模扩增可能倾向于进化的毒蛋白酶在社会蚜虫血统，并认为，基因复制，加速分子进化，并获得新的基因功能，必须发挥了相当大的作用，在复杂的生物系统，包括昆虫社会性的进化。
In social aphids of the genus Tuberaphis a cysteine protease gene of the family cathepsin B exhibits soldier-specific expression and intestinal protease production. The product is orally excreted and injected by soldier nymphs into natural enemies, thereby exerting an insecticidal activity. In an attempt to gain insights into when and how the novel venomous protease for the altruistic caste has evolved, we investigated the soldier-specific type (S-type) and nonspecific type (N-type) cathepsin B genes from social and nonsocial aphids. All the social aphids examined, representing the genera Tuberaphis, Astegopteryx, and Cerataphis, possessed both the S-type and N-type genes. Phylogenetically distant nonsocial aphids also possessed cathepsin B genes allied to the S-type and the N-type, indicating the evolutionary origin of these genes in the common ancestor of extant aphids. In Tuberaphis species the S-type genes exhibited significant soldier-specific expression and accelerated molecular evolution whereas the N-type genes did not. In Astegopteryx and Cerataphis species, meanwhile, both the S-type and N-type genes exhibited neither remarkable soldier-specific expression nor accelerated molecular evolution. These results suggest that the S-type gene acquired the soldier-specific expression and the venom function after divergence of the genus Tuberaphis. On the structural model of the S-type protease of Tuberaphis styraci the accelerated molecular evolution was associated with the molecular surface rather than the catalytic cleft, suggesting that the venom activity was probably acquired by relatively minor modifications on the molecular surface rather than by generation of a novel active site. In Cerataphis jamuritsu the S-type gene was, although containing a stop codon, structurally almost intact and still transcribed, suggesting recent pseudogenization of the gene copy and possible relevance to relaxed functional constraint in the highly multiplied protease gene family. On the basis of these results we suggest that the massive amplification in aphid cathepsin B genes might have predisposed the evolution of venomous protease in the social aphid lineage and argue that gene duplication, accelerated molecular evolution, and acquisition of novel gene function must have played considerable roles in the evolution of complex biological systems including insect sociality.