Genome sequence of the wheat stem sawfly, Cephus cinctus, representing an early-branching lineage of the Hymenoptera, illuminates evolution of hymenopteran chemoreceptors

Authors: ROBERSON, HUGH - University Of Illinois; WALDEN, KIM - University Of Illinois; RUZZANTE, LIVIO - University Of Lausanne; REIJNDERS, MAARTEN - University Of Lausanne; WATERHOUSE, ROBERT - University Of Lausanne; Coates, Brad; LEGEAI, FABRICE - Institut National De La Recherche Agronomique (INRA); GRESS, JOANNE - Abraham Baldwin Agricultural College; BIYIKLIOGLU, SEZGI - Montana State University; WEAVER, DAVID - Montana State University; WANNER, KEVIN - Montana State University; BUDAK, HIKMET - Montana State University

Submitted to: Genome Biology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/12/2018
Publication Date: 11/1/2018
Citation: Roberson, H.M., Walden, K.O., Ruzzante, L., Reijnders, M., Waterhouse, R.M., Coates, B.S., Legeai, F., Gress, J.C., Biyiklioglu, S., Weaver, D.K., Wanner, K.W., Budak, H. 2018. Genome sequence of the wheat stem sawfly, Cephus cinctus, representing an early-branching lineage of the Hymenoptera, illuminates evolution of hymenopteran chemoreceptors. Genome Biology and Evolution. 10(11):2997-3011. https://doi.org/10.1093/gbe/evy232.
DOI: https://doi.org/10.1093/gbe/evy232

Interpretive Summary: The wheat stem sawfly is a major insect pest of cultivated wheat in the United States. Due to the life cycle of this species, larvae cause damage to winter wheat resulting in plant lodging and yield loss. Following a recent shift in the life cycle, larvae within a subpopulation of wheat stem sawfly now cause analogous damage to spring wheat crops. A whole genome sequence assembly was generated for the wheat stem sawfly. Chemoreceptors are important proteins involved in insect reproduction and interaction with their environment, including host plant recognition. The chemoreceptor genes were investigated within the wheat stem sawfly genome to define expression patterns, potential functions, and changes in gene content compared to related species. These data will be important for understanding insect perception in relation to crop host plant recognition and mating strategies, and may provide information regarding potential targets for species-specific insect pest control. The genome will provide a foundation for future research by public and private sector scientists on the adaptation of insect species to farmer practices.

Technical Abstract: The wheat stem sawfly, Cephus cinctus, is a major pest of wheat and a significant ecological player in grasslands in North America. It also represents a distinctive lineage of sawflies belonging phylogenetically between the Eusymphyta and the parasitic woodwasp superfamily of Orussoidea at the base of the Hymenoptera. We present a high-quality draft genome assembly of 162 Mbp in 1,976 scaffolds with a scaffold N50 of 622 kbp. Automated gene annotation resulted in 11,210 protein-coding gene models and 1,307 non-coding RNA models. Phylogenomic analysis of conserved subsets of these proteins supports the above phylogenetic location of the Cephidae. Orthology analysis reveals that 86% of Cephus proteins have othologs in other insects. 21 Mb of the assembly consists of ~58,000 transposable elements split equally between Class-I and Class-II elements. Manual annotation of the odorant, gustatory, and ionotropic receptors, as well as the odorant binding proteins, revealed that the Cephus genes provide basal representatives for most conserved and expanded gene lineages in the Apocrita (wasps, ants, and bees). Several Cephus gene lineages were lost from the Apocrita, however, most prominently the carbon dioxide receptor subfamily. There are only a few small Cephus-specific chemoreceptor gene expansions that might be involved in adaptation to new grasses including wheat.