Small genome symbiont underlies cuticle hardness in beetles

Authors: Hisashi Anbutsu, Minoru Moriyama, Naruo Nikoh, Takahiro Hosokawa, Ryo Futahashi, Masahiko Tanahashi, Xian-Ying Meng, Takashi Kuriwada, Naoki Mori, Kenshiro Oshima, Masahira Hattori, Manabu Fujie, Noriyuki Satoh, Taro Maeda, Shuji Shigenobu, Ryuichi Koga, Takema Fukatsu - Proceedings of the National Academy of Sciences, PNAS 2017 cited by 175

Significance Beetles are successful in the terrestrial ecosystem, which is attributable to, at least partly, their highly sclerotized exoskeleton. Here, we report a bacterial symbiont extremely specialized for underpinning the beetle’s hardness. The ancient endosymbiont Nardonella associated with weevils has an extremely small genome devoted to a single biological function, tyrosine provisioning, which is needed for insect’s cuticle formation and hardening. Notably, only the final step reaction of the tyrosine synthesis pathway is complemented by host-encoded aminotransferases up-regulated in the bacteriome, highlighting a highly focused aspect of the host–symbiont metabolic integrity. Both symbiont suppression by an antibiotic and RNA interference of the host aminotransferases induce reddish and soft weevils, verifying the pivotal role of the symbiosis for the beetle’s hardness.