The Genomic Basis of Wax Biosynthesis in Scale Insects
Kenadie Glasgow1; Zinan Wang2; and Zheng Li1
1Department of Biology Miami University; 2Department of Entomology, University of Kentucky
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Introduction
The extensive production of wax is a key innovation that has promoted the protection of scale insects (Ross et al. 2009). Wax biosynthesis is controlled through the expression of different genes in epidermal tissue. The importance of the expression of wax biosynthesis genes has been studied, but the genomic basis of these genes is not fully understood (Gullan et al. 1997). This project aims to understand how key innovations arose from the genome by studying the genomic basis of wax production in scale insects. This will be studied through the identification of candidate wax biosynthesis genes in the crapemyrtle bark scale, Acanthococcus lagerstroemiae, inference of how these genes diversified, and exploration of their copy numbers in scale insects and other hemipteran insects.
Scale insects
Scale insects
Figure 1. Photos of different species of scale insects and mealybugs: Cottony cushion scale (A), Oleander scale (B), Giant mealybug (C), Indian wax scale (D) Florida red scale (E), Crapemyrtle bark scale (F), Gloomy scale (G), Gill’s mealybug (H).
Life Cycle
Life Cycle
Figure 2. Life cycle of the crypemyrtle bark scale. Shows differentiation between the life cycle of male and female.
Methods
We evaluated candidate genes by accessing known wax biosynthesis proteins from Drosophila melanogaster and Ericerus pela (Chinese white wax scale insect).
OrthoFinder was used to cluster gene families into orthogroups, allowing for the identification of gene copy numbers across several insect genomes.
The genomic distribution of these genes in the crapemyrtle bark scale was presented using RIdeogram (Hao et al. 2020).
Copy numbers of wax biosynthesis genes in other insects were visualized in a heat map.
Results
Results
SEM Images of Wax Production
SEM Images of Wax Production
Figure 3. Scanning Electron Microscopy (SEM) images of the wax that is produced from the crapemyrtle bark scale insect. Wax is secreted through pores all over the body. Wax is mainly composed for hydrocarbons and wax esters (Tamaki 1969).
RIdeogram
RIdeogram
Figure 4. Ideogram with chromosomal locations of the gene families of diacylglycerol acyltransferase (DGAT), fatty acid elongase (ELO), desaturase genes (Desat), fatty acid reductase (Reductase) and fatty acid synthase (FASN) the crapemyrtle bark scale genome. The intensity of the color on each chromosome represents gene density. Expansion through tandem duplication is evident by many gene copies of gene families being in close proximity on chromosomes.
Heat Map
Heat Map
Figure 5. The heat map shows the rates of expression of wax biosynthesis genes in several different insect families. This is represented in the first column as the insects highlighted yellow are scale insects and mealybugs, blue are aphids, adelgids, and phylloxera, red are other Sternorrhyncha, and white are outgroups. The top row represents candidate genes (left to right): diacylglycerol acyltransferase (DGAT), fatty acid synthase (FASN), fatty acid desaturase genes (Desat), fatty acid elongase (ELO), and fatty acid reductase (Reductase). In other columns, the gene number of each gene family is provided, intense color represents a higher gene number.
Conclusion
Five wax biosynthesis gene families were identified as DGAT, FASN, Desat, ELO, and Reductase.
High copy numbers seen in scale insects are driven by tandem duplication.
Higher observed copy numbers were seen in gene families of DGAT and FASN compared to other hemipteran insects.
Future Work
RNAseq and Differential expression analysis on epidermis tissue vs. control tissue of crapemyrtle bark scale.
Build gene family phylogenies to understand their evolutionary history.
Investigate chromosomal evolution of scale insects using synteny analyses.
Genome editing using CRISPR/ Cas9 on candidate genes (In collaboration with Wang lab at U. of Kentucky).
Researchers
Kenadie Glasgow
Kenadie Glasgow
Undergraduate in Biology at Miami University
Zheng Li, Ph.D.
Zheng Li, Ph.D.
Assistant Professor; Herbarium Director in the Department of Biology, Miami University
Zinan Wang, Ph.D.
Zinan Wang, Ph.D.
Assistant professor in the Department of Entomology at the University of Kentucky
Acknowledgments and References
Acknowledgments: We acknowledge the Miami Redhawk cluster for their computational support.
Acknowledgments: We acknowledge the Miami Redhawk cluster for their computational support.
References:
References:
Emms, D.M., Kelly, S. OrthoFinder: phylogenetic orthology inference for comparative genomics. Genome Biol 20, 238 (2019). https://doi.org/10.1186/s13059-019-1832-y
Gullan, Penny J., Kosztarab, M., Adaptations in scale insect. Annual Review of Entomology, Volume 42, 23-50 (1997). https://www.annualreviews.org/content/journals/10.1146/annurev.ento.42.1.23
Hao, Z., Lv, D., Ge, Y., RIdeogram: drawing SVG graphics to visualize and map genome-wide data on the idiograms. PeerJ Computer Science, (2020). https://peerj.com/articles/cs-251/
Ross, L., Shuker, David M., Quick guide: Scale Insects. Current Biology, Volume 19, No. 5, 184-186 (2009). https://doi.org/10.1016/j.cub.2008.12.023
Tamaki, Y., Yushima, T., Kawai, S., Wax secretion in a scale insect, Ceroplastes pseudoceriferus GREEN (Homoptera : Coccidae). Applied Entomology and Zoology, Volume 4, No. 3, 126-134 (1969). https://www.jstage.jst.go.jp/article/aez1966/4/3/4_3_126/_article/-char/ja/
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