In vivo expression of genes in the entomopathogenic fungus Beauveria bassiana during infection of lepidopteran larvae

Lineage-specific gene evolution of innate immunity in Bombyx mori to adapt to challenge by pathogens, especially entomopathogenic fungi

Bombyx mori is a model species of Lepidoptera, in which 21 gene families and 220 genes have been identified as involved in immunity. However, only 45 B. mori - Drosophila melanogaster - Anopheles gambiae - Apis mellifera - Tribolium castaneum 1:1:1:1:1 orthologous genes were identified. B. mori has unique immune factors not found in D. melanogaster - A. gambiae - A. mellifera - T. castaneum. Pattern recognition receptors, signal transducers and effector genes for antifungal immune responses in B. mori have evolved through expansion and modification of existing genes. This review summarizes the current knowledge of the antifungal immune responses of B. mori and focuses on the lineage-specific gene evolution used by Lepidoptera to adapt to the challenge by pathogens, especially entomopathogenic fungi.

Molecular characterization of pathogenesis involving the GAS 1 gene from Entomopathogenic fungus Lecanicillium lecanii and its virulence against the insect host Diaphorina citri

The entmopathogenic fungus Lecaniicillium lecanii is a naturally available biological control and it is considered to be one of the best mycoinsecticide agents against the destructive insect pest Diaphorina citri Kuwayama. The present study aimed to extract and characterize the toxic insecticidal protein from L. lecanii and to assess the toxicity level against the Asian citrus psyllid the vector of Huanglongbing disease (HLB), also called citrus greening. Extracts of a toxic substance from submerged batch culture examined by sodium dodecyl sulfate-poly-acrylamide (SDS-PAGE), had a molecular weight of 45 kDa. The most abundant toxic metabolite was subjected to HPLC to purify and identified it by mass spectrometry. Subsequently, metabolite toxicity was tested against D. citri at three different concentrations (1%, 2%, and 3%). The results showed that the highest concentration had a significant maximum mortality at 120 h post application. Furthermore, we investigated the expression of the GAS1 gene which was previously identified to have a role in pathogenicity in in vivo studies in adult insect psyllids. Results of this study indicated that expression of the virulence factor gene was present at three concentrations of the fungal suspension post inoculation. This is the first study to provide this novel approach for the characterization of fungal mediated synthesis of a cuticle degrading soluble protein against the insect D. citri. The present results provide strong information on the in vivo expression of the GAS1 gene involved in fungal virulence pertaining to penetration of the insect cuticle, but not to inhibiting the growth of the host.

Variation in virulence of Beauveria bassiana and B. pseudobassiana to the pine weevil Pissodes nemorensis in relation to mycelium characteristics and virulence genes

Entomopathogenic fungi such as Beauveria spp. have potential applications in the biocontrol of insect pests but little is known regarding their infectivity to the pine weevil Pissodes nemorensis. In this study, five isolates of Beauveria pseudobassiana and five isolates of Beauveria bassiana were tested for characteristics correlating with virulence on P. nemorensis. Isolate UAMH301 had the lowest mean lethal concentration value whereas the highest value was obtained with isolate LRC137. Growth rate was negatively correlated with virulence in B. bassiana, because isolate LRC137, the least virulent isolate, grew much more rapidly than the other B. bassiana isolates on SDYA. In contrast, its growth on a hyperosmotic medium was the slowest. Sporulation rate and conidial area were not correlated with virulence. Mycelial cell density was positively correlated with virulence in both species, and the four tested genes appear to be one-copy genes. Bbchit1 and Bbhog1, genes respectively encoding a chitinase and a protein kinase, induced relative expression levels were positively correlated with virulence in B. pseudobassiana. We discuss in terms of previous morphological, physiological and genetic parameters related to virulence in Beauveria and the importance of testing the expression of putative virulence genes in comparison with their basal transcript levels.