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ARS Home » Southeast Area » Gainesville, Florida » Center for Medical, Agricultural and Veterinary Entomology » Insect Behavior and Biocontrol Research » Research » Publications at this Location » Publication #324038

Title: Fungal dimorphism in the entomopathogenic fungus Metarhizium rileyi: detection of an in vivo quorum-sensing system

Author
item BOUCIAS, D - University Of Florida
item LIU, S - Liaocheng University
item Meagher, Robert - Rob
item BANISZEWSKI, J - University Of Florida

Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/22/2016
Publication Date: 5/1/2016
Citation: Boucias, D., Liu, S., Meagher Jr, R.L., Baniszewski, J. 2016. Fungal dimorphism in the entomopathogenic fungus Metarhizium rileyi: detection of an in vivo quorum-sensing system. Journal of Invertebrate Pathology. 136:100-108. https://doi.org/10.1016/j.jip.2016.03.013.
DOI: https://doi.org/10.1016/j.jip.2016.03.013

Interpretive Summary: All insect species, including pests, have bacterial, viral, and fungal diseases. These pathogens, when applied to crop plants, can help manage insect populations. The way that different fungal diseases attack and kill caterpillars is not completely understood. Scientists from the University of Florida and a researcher with USDA, Agriculture Research Service, Center for Medical, Agricultural and Veterinary Entomology, Gainesville, Florida, used the caterpillars of two moths, beet armyworm and cabbage looper, to learn more about the sequence of infection of a pathogenic fungal species, Metarhizium rileyi. Results showed that after contact, the caterpillar produces chemicals in response to the fungus. The fungus in turn detects these chemicals and then switches to produce a more invasive and pathogenic stage. Attempts were made to identify the signaling chemicals produced by the caterpillars but they remain unidentified. The findings demonstrate that the relationship between fungus and insect is much more complicated than previously thought and that through a more complete understanding of the pathogenesis will lead to a more effective use of pathogenic fungi to control insect pests.

Technical Abstract: This investigation documents the expression of the in vivo dimorphic program exhibited by insect mycopathogen M. rileyi replicating. This insect mycopathogen represents the key mortality factor regulating various caterpillar populations in various legumes, including subtropical and tropical soybeans. Using multiple hosts and M. rileyi isolates, we have measured M. rileyi growth rates under in vivo and in vitro conditions, and assessed the pathogen’s impact on host fitness. Significantly, the hyphal bodies-to mycelia transition that occurs at the late infection stage is regulated by a potential blend of quorum sensing molecules (QSM) that triggers hyphal bodies (Hb) to synchronously switch to the tissue invasive mycelia. Within hours of this transition, the host insect succumbs to mycosis. The production of these QS chemicals occurs when a quorum of Hb is produced in the hemolymph (late-stage infection). Furthermore, the QS activity detected in late-stage infected sera is unique and is unrelated to any known fungal QSM. The lack of similar QSM activity from conditioned media of M. rileyi suggests that the chemical signal(s) that mediates the dimorphic switch is produced by host tissues in response to a quorum of hyphal bodies produced in the host hemolymph. The serum based QS activity is retained after lyophilization, mild heat treatment, and proteinase digestion. However, attempts to extract/identify the QSM have been unsuccessful. Results suggest that the observed hyphal body-to-mycelia transition is a multi-step process involving more than one chemical signal.