1887

Abstract

Neuronal calcium sensor proteins and their homologues participate in transducing extracellular signals that affect intracellular Ca levels, which in turn regulate enzyme activities, secretion, gene expression and other biological processes. The filamentous fungus is a broad-host-range pathogen of insects that acidifies the extracellular milieu during growth and pathogenesis towards target hosts. A collection of random insertion mutants were screened on pH indicator plates and one mutant was isolated that displayed reduced acidification. The random insertion site was mapped to a gene that displayed homology to the neuronal calcium sensor/frequenin protein family and was designated . To validate the role of in , a targeted gene-knockout was constructed. Data confirmed that was not an essential gene and the Δ strain displayed delayed acidification of the medium when grown in Czapek–Dox medium, as compared with the wild-type parent. HPLC profiling of secreted metabolites did not detect any major changes in the production of organic acids, although downregulation of the membrane H pump/ATPase was noted in the mutant. A slight growth-deficient phenotype was observed for the Δ strain on Czapek–Dox and potato dextrose media, which was accentuated at high calcium concentrations (500 mM) and 1.5 M sorbitol, but was unaffected by EDTA or SDS. Perturbations in vacuole morphology were also noted for the mutant. Insect bioassays using as the target host revealed decreased virulence in the Δ mutant when applied topically, representing the natural route of infection, but no significant effect was observed when fungal cells were directly injected into target hosts. These results suggest that participates in pre-penetration or early penetration events, but is dispensable once the insect cuticle has been breached.

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2012-07-01
2019-10-17
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