Genome size evolution in the beetle genus Diabrotica

Authors: LATA, DIMPAL - Illinois Institute Of Technology; Coates, Brad; WALDEN, KIMBERLY K - University Of Illinois; ROBERTSON, HUGH - University Of Illinois; MILLER, NICHOLAS - Illinois Institute Of Technology

Submitted to: bioRxiv
Publication Type: Pre-print Publication
Publication Acceptance Date: 9/6/2021
Publication Date: 9/6/2021
Citation: Lata, D., Coates, B.S., Walden, K.O., Robertson, H.M., Miller, N.J. 2021. Genome size evolution in the beetle genus Diabrotica. bioRxiv. Article 458993. https://doi.org/10.1101/2021.09.04.458993.
DOI: https://doi.org/10.1101/2021.09.04.458993

Interpretive Summary: Corn rootworm are pest insect species that causes damage to cultivate corn across the most regions of the United States. The western corn rootworm (WCR) and the northern corn rootworm (NCR) feed almost exclusively on corn and cause significant amounts of damage to this crop across the Midwest. In contrast, the southern corn rootworm (SCR) feeds on multiple grasses and is a less severe pest of corn in southern regions of the United States. Resistance by WCR and NCR to multiple insecticides commonly used by growers threatens the sustainability of current corn production practices, but similar resistance has not developed in SCR. Changes in the genomes between these corn rootworms that leads to these differences remains unknown. A USDA scientist at the Corn Insects and Crop Genetics Research Unit in Ames, Iowa, along with university collaborators determined the genome size and composition of WCR, NCR, SCR and closely related species. The genome size of WCR and NCR was shown to be nearly 1.6-fold larger compared to SCR. This increase in size was due to expansion in the number of repeated sequences in the genome. Repeats were identified as belonging to different classes of DNA elements that are capable of copying and moving themselves to different genome locations. The expansion in genome size due to corresponding increase in copy number of these mobile DNA elements was unique to WCR and NCR. This study provides unique information on the structure and evolution of genomes for corn rootworm species, and provides important information for future genomic research. This research is of interest to public and private sector scientists involved in the genomics of corn rootworms, and investigating differences in feeding preference and abilities to become resistant to insecticides.

Technical Abstract: Diabrocite corn rootworms are one of the most economically significant pests of maize in the United States and Europe and an emerging model for insect-plant interactions. Genome sizes of several species in the genus Diabrotica were estimated using flow cytometry along with that of Acalymma vittatum as an outgroup. Within the Diabrotica subgroups fucata and virgifera, genome sizes ranged between 1.59 - 1.69 gigabase pairs (Gbp) and between 2.31- 2.65 Gbp, respectively, and the Acalymma vittatum genome size was around 1.69 Gb. This result indicated that a substantial increase in genome size occurred in the ancestor of the virgifera group. Further analysis of fucata group and virgifera group genome sequencing reads indicated that the genome size difference between the Diabrotica subgroups could be attributed to a higher content of transposable elements, mostly miniature inverted-transposable elements (MITEs) and LTR gypsy-like elements.