Related Experiment Video
Updated: May 13, 2026
Delivery of Nucleic Acids through Embryo Microinjection in the Worldwide Agricultural Pest Insect, Ceratitis capitata
Published on: October 1, 2016
Insertion of an esterase gene into a specific locust pathogen (Metarhizium acridum) enables it to infect caterpillars
Sibao Wang1, Weiguo Fang, Chengshu Wang
1Department of Entomology, University of Maryland, College Park, Maryland, United States of America.
Abstract:
An enduring theme in pathogenic microbiology is poor understanding of the mechanisms of host specificity. Metarhizium is a cosmopolitan genus of invertebrate pathogens that contains generalist species with broad host ranges such as M. robertsii (formerly known as M. anisopliae var. anisopliae) as well as specialists such as the acridid-specific grasshopper pathogen M. acridum. During growth on caterpillar (Manduca sexta) cuticle, M. robertsii up-regulates a gene (Mest1) that is absent in M. acridum and most other fungi. Disrupting M. robertsii Mest1 reduced virulence and overexpression increased virulence to caterpillars (Galleria mellonella and M. sexta), while virulence to grasshoppers (Melanoplus femurrubrum) was unaffected. When Mest1 was transferred to M. acridum under control of its native M. robertsii promoter, the transformants killed and colonized caterpillars in a similar fashion to M. robertsii. MEST1 localized exclusively to lipid droplets in M. robertsii conidia and infection structures was up-regulated during nutrient deprivation and had esterase activity against lipids with short chain fatty acids. The mobilization of stored lipids was delayed in the Mest1 disruptant mutant. Overall, our results suggest that expression of Mest1 allows rapid hydrolysis of stored lipids, and promotes germination and infection structure formation by M. robertsii during nutrient deprivation and invasion, while Mest1 expression in M. acridum broadens its host range by bypassing the regulatory signals found on natural hosts that trigger the mobilization of endogenous nutrient reserves. This study suggests that speciation in an insect pathogen could potentially be driven by host shifts resulting from changes in a single gene.
Insights
A single gene, Mest1, enables the fungus Metarhizium robertsii to infect caterpillars by rapidly hydrolyzing lipids. Transferring this gene to a grasshopper pathogen broadened its host range, suggesting single genes can drive fungal speciation.
Area of Science:
- Pathogenic microbiology
- Fungal genetics
- Insect pathology
Background:
- Host specificity in fungal pathogens remains poorly understood.
- Metarhizium fungi exhibit diverse host ranges, from generalists to specialists.
- M. robertsii infects caterpillars, while M. acridum is grasshopper-specific.
Purpose of the Study:
- Investigate the role of the Mest1 gene in Metarhizium host specificity.
- Determine if Mest1 can broaden the host range of specialist fungi.
Main Methods:
- Gene disruption and overexpression in M. robertsii.
- Gene transfer of Mest1 into M. acridum.
- Virulence assays on caterpillars and grasshoppers.
- Microscopic localization and biochemical assays of MEST1 protein.
Main Results:
- Disrupting Mest1 reduced M. robertsii virulence to caterpillars but not grasshoppers.
- Overexpressing Mest1 enhanced caterpillar infection.
- Transferring Mest1 to M. acridum enabled caterpillar infection.
- MEST1 hydrolyzes lipids, aiding nutrient mobilization during infection.
Conclusions:
- Mest1 facilitates rapid lipid hydrolysis, promoting fungal germination and infection structure formation.
- Mest1 expression in M. acridum bypasses host regulatory signals, broadening its host range.
- Changes in a single gene, like Mest1, may drive speciation in insect pathogens.
