The Msn2 transcription factor regulates acaricidal virulence in the fungal pathogen Beauveria bassiana
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2021
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Resumo
Beauveria bassiana holds promise as a feasible biological control agent for tick control.
The B. bassiana stress–response transcription factor Msn2 is known to contribute to
fungal growth, conidiogenesis, stress–response and virulence towards insects; however,
little is known concerning whether Msn2 is involved in infection across Arthropoda
classes. We evaluated the effects of Msn2 on B. bassiana virulence against
Rhipicephalus microplus (Acari, Ixodidae) using wild-type, targeted gene knockout
(DBbmsn2) and complemented mutant (DBbmsn2/Bbmsn2) strains. Reproductive
parameters of R. microplus engorged females treated topically or by an intra-hemocoel
injection of conidial suspensions were assessed. Treated cuticles of engorged females
were analyzed by microscopy, and proteolytic activity of B. bassiana on cuticles was
assessed. Topically treated engorged females showed high mean larval hatching (>84%)
in control and DBbmsn2 treatments, whereas treatment with the wild-type or DBbmsn2/
Bbmsn2 strains resulted in significantly decreased (lowered egg viability) larval hatching.
Percent control of R. microplus topically treated with DBbmsn2 was lower than in the
groups treated with wild-type (56.1%) or DBbmsn2/Bbmsn2 strains. However, no
differences on reproductive parameters were detected when R. microplus were treated
by intra-hemocoel injection using low (800 conidia/tick) doses for all strains tested; R.
microplus injected with high doses of wild-type or mutant strains (106 conidia/tick) died
before laying eggs (~48 h after treatment). SEM analyses of B. bassiana infection showed
similar conidial germination and formation of pseudo-appressoria on tick cuticle.
Histological sections of ticks treated with the wild-type or DBbmsn2/Bbmsn2 strains
showed fungal penetration through the cuticle, and into the tick interior. Hyphae
of DBbmsn2, however, did not appear to penetrate or breach the tick exocuticle 120 h
after treatment. Protease activity was lower on tick cuticles treated with DBbmsn2 than
those treated with the wild-type or DBbmsn2/Bbmsn2 strains. These data show that loss
of the Msn2 transcription factor reduced B. bassiana virulence against R. microplus, but
did not interfere with conidial germination, appressoria formation or sporulation on tick
cadavers, and plays only a minimal role once the cuticle is breached. Our results indicate
that the BbMsn2 transcription factor acts mainly during the fungal penetration process and that decreased protease production may be one mechanism that contributes to the
inability of the mutant strain to breach the tick cuticle.
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Tick, Biological control, Entomopathogenic fungi, Cuticle, Virulence, Beauveria bassiana, Rhipicephalus microplus, Msn2
Citação
MUNIZ, Elen R. et al. The Msn2 transcription factor regulates acaricidal virulence in the fungal pathogen Beauveria bassiana. Frontiers in Cellular and Infection Microbiology, Lausanne, v. 11, e690731, 2021. DOI: 10.3389/fcimb.2021.690731. Disponível em: https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2021.690731/full. Acesso em: 11 dez. 2024.