Comparative Genomics of the Dual-Obligate Symbionts from the Treehopper, Entylia carinata (Hemiptera: Membracidae), Provide Insight into the Origins and Evolution of an Ancient Symbiosis

Abstract

Insect species in the Auchenorrhyncha suborder (Hemiptera) maintain ancient obligate symbioses with bacteria that provide essential amino acids (EAAs) deficient in their plant-sap diets. Molecular studies have revealed that two complementary symbiont lineages, “Candidatus Sulcia muelleri” and a betaproteobacterium (“Ca. Zinderia insecticola” in spittlebugs [Cercopoidea] and “Ca. Nasuia deltocephalinicola” in leafhoppers [Cicadellidae]) may have persisted in the suborder since its origin ∼300 Ma. However, investigation of how this pair has co-evolved on a genomic level is limited to only a few host lineages. We sequenced the complete genomes of Sulcia and a betaproteobacterium from the treehopper, Entylia carinata (Membracidae: ENCA), as the first representative from this species-rich group. It also offers the opportunity to compare symbiont evolution across a major insect group, the Membracoidea (leafhoppers + treehoppers). Genomic analyses show that the betaproteobacteria in ENCA is a member of the Nasuia lineage. Both symbionts have larger genomes (Sulcia = 218 kb and Nasuia = 144 kb) than related lineages in Deltocephalinae leafhoppers, retaining genes involved in basic cellular functions and information processing. Nasuia-ENCA further exhibits few unique gene losses, suggesting that its parent lineage in the common ancestor to the Membracoidea was already highly reduced. Sulcia-ENCA has lost the abilities to synthesize menaquinone cofactor and to complete the synthesis of the branched-chain EAAs. Both capabilities are conserved in other Sulcia lineages sequenced from across the Auchenorrhyncha. Finally, metagenomic sequencing recovered the partial genome of an Arsenophonus symbiont, although it infects only 20% of individuals indicating a facultative role.

Comparative genomics of a quadripartite symbiosis in a planthopper host reveals the origins and rearranged nutritional responsibilities of anciently diverged bacterial lineages

“…Recent phylogenetic analyses suggest that the original partner of Sulcia is a Betaproteobacteria ancestor whose descendants can still be found in the major Auchenorrhyncha lineages (Urban and Cryan, ; Koga et al ., ; Mao et al ., ). Our results provide additional support for this hypothesis by including Vidania within a clade of Betaproteobacteria symbionts associated with the suborder.…”

“…Vidania-OLIH does not appear to use an alternate genetic code (Stop ! Trp), which was used as an additional character for inferring a common origin for Nasuia and Zinderia-CARI (McCutcheon and Moran, 2010;Bennett and Moran, 2013;Mao et al, 2017). It is possible that the Betaproteobacteria lineage in the Cicadomorpha uniquely lost the prfB gene and that an altered genetic code is an apomorphic trait for this lineage.…”

“…and 'Ca. Zinderia insecticola' (Betaproteobacteria) provide the missing two or three EAAs respectively McCutcheon and Moran, 2010;Mao et al, 2017). This nutritional arrangement is highly conserved, even when Sulcia's partners have been occasionally replaced in the cicadas, sharpshooter leafhoppers, and spittlebugs (Wu et al, 2006;Koga and Moran, 2014;McCutcheon and Moran, 2007;McCutcheon et al, 2009).…”

Match and mismatch between dietary switches and microbial partners in plant sap-feeding insects

“…Zinderia insecticola in spittlebugs, or more generally as a 'companion symbiont' to Sulcia [23 -27]. Some auchenorrhynchans, however, bear Sulcia as the sole symbiont, associate with a companion symbiont other than b-Sym [28][29][30][31], or have ascomycete fungal symbionts, generically known as yeast-like symbionts (YLS) [32 -35]. This rich diversity of symbionts with functions closely tied to host diet provides a superb basis to test the relationship between switches in diet and symbiont identity.…”

To B or not to B: Arsenophonus as a source of B-vitamins in whiteflies

“…This could explain why the capability to produce some of these compounds has been kept in bacterial endosymbionts while it has been lost in others. However, the production of one or several B vitamins (thiamine, riboflavin, pyridoxal, folate, and biotin) and de novo lipoate by whiteflies’ Arsenophonus seems to be the main contribution of these endosymbionts to their hosts, allowing them to feed on the limited diet present in the phloem (Dale et al, 2006; Nováková et al, 2015, 2016; Mao et al, 2017). Regarding biotin biosynthesis, the bacterial origin of bioAB and bioD was reported by Luan et al (2015) and Ankrah et al (2017).…”