Development of an expression vector for Metarhizium anisopliae based on the tef-1alpha homologous promoter

Screening of high toxic Metarhizium strain against Plutella xylostella and its marking with green fluorescent protein

Entomopathogenic fungus is proposed to be one of the best biocontrol agents against the destructive insect pest Plutella xylostella. In this study, we tested the virulence of 11 Metarhizium strain isolates against P. xylostella using a leaf dipping method, and found one strain, named 609, which had displayed the highest pathogenicity. Bioassay results showed that the accumulated corrected mortality rate was 86.7 % on the eighth day after inoculation with a spore concentration 1 × 10(8) conidia/mL, and that the time to 50 % lethality was 5.7-day. The strain was identified as Metarhizium anisopliae var. acridum by internal transcribed spacer (ITS) region sequencing. A green fluorescent protein (GFP) marker containing vector, camben-gfp, was constructed and delivered into strain 609 by Agrobacterium tumefaciens-mediated transformation. Six positive clones expressing GFP were selected and tested for toxicity against P. xylostella, all of which displayed the same toxicity as the parental wild type strain. The survival rate of transformant T1 was investigated by monitoring GFP levels at 4-day intervals after inoculation into soil. We found that the concentration of Metarhizium spores decreased sharply from 1 × 10(7) conidia/g to 1 × 10(6) conidia/g in the first 5 days after inoculation. The decreasing trend then stabilized and the spore count declined to approximately 1 × 10(4)-10(5) conidia/g after 1 month. The results of this study indicate that the expression of gfp gene in strain 609 does not alter the virulence capability of Metarhizium. This strain will therefore be useful for the control of P. xylostella and as a tool to study molecular biology properties and monitor colonization of M. anisopliae in the field.

Variability in the insect and plant adhesins, Mad1 and Mad2, within the fungal genus metarhizium suggest plant adaptation as an evolutionary force

Several species of the insect pathogenic fungus Metarhizium are associated with certain plant types and genome analyses suggested a bifunctional lifestyle; as an insect pathogen and as a plant symbiont. Here we wanted to explore whether there was more variation in genes devoted to plant association (Mad2) or to insect association (Mad1) overall in the genus Metarhizium. Greater divergence within the genus Metarhizium in one of these genes may provide evidence for whether host insect or plant is a driving force in adaptation and evolution in the genus Metarhizium. We compared differences in variation in the insect adhesin gene, Mad1, which enables attachment to insect cuticle, and the plant adhesin gene, Mad2, which enables attachment to plants. Overall variation for the Mad1 promoter region (7.1%), Mad1 open reading frame (6.7%), and Mad2 open reading frame (7.4%) were similar, while it was higher in the Mad2 promoter region (9.9%). Analysis of the transcriptional elements within the Mad2 promoter region revealed variable STRE, PDS, degenerative TATA box, and TATA box-like regions, while this level of variation was not found for Mad1. Sequences were also phylogenetically compared to EF-1α, which is used for species identification, in 14 isolates representing 7 different species in the genus Metarhizium. Phylogenetic analysis demonstrated that the Mad2 phylogeny is more congruent with 5′ EF-1α than Mad1. This would suggest that Mad2 has diverged among Metarhizium lineages, contributing to clade- and species-specific variation, while it appears that Mad1 has been largely conserved. While other abiotic and biotic factors cannot be excluded in contributing to divergence, these results suggest that plant relationships, rather than insect host, have been a major driving factor in the divergence of the genus Metarhizium.

Recognition of a core fragment ofBeauveria bassiana hydrophobin gene promoter (P hyd1) and its special use in improving fungal biocontrol potential

To identify a suitable promoter for use in engineering fungal entomopathogens to improve heterologous gene expression and fungal biocontrol potential, a 1798 bp promoter (P hyd1) upstream of Beauveria bassiana class I hydrophobin gene (hyd1) was optimized by upstream truncation and site-directed mutation. A truncated 1290 bp fragment (P hyd1-t1) drove eGFP expression in B. bassiana much more efficiently than full-length P hyd1. Further truncating P hyd1-t1 to 1179, 991 and 791 bp or mutating one of the binding domains of three transcription factors in P hyd1-t1 reduced significantly the expression of eGFP (enhanced green fluorescence protein). Under P hyd1-t1 control, eGFP was expressed more abundantly in conidiogenic cells and conidia than in mycelia. Therefore, P hyd1-t1 was used to integrate a bacterium-derived, insect midgut-specific toxin (vip3Aa1) gene into B. bassiana, yielding a transgenic strain (BbHV8) expressing 9.8-fold more toxin molecules in conidia than a counterpart strain (BbV28) expressing the toxin under the control of P gpdA, a promoter widely used for gene expression in fungi. Consequently, BbHV8 showed much higher per os virulence to Spodoptera litura larvae than BbV28 in standardized bioassays with normal conidia for both cuticle penetration and ingestion or heat-killed conidia for ingestion only. Conclusively, P hyd1-t1 is a useful tool for enhancing beneficial protein expression, such as vip3Aa1, in fungal conidia, which are the active ingredients of mycoinsecticides.

Agrobacterium tumefaciens-mediated transformation of Guignardia citricarpa

Guignardia citricarpa, the causal agent of Citrus Black Spot, was successfully transformed via Agrobacterium tumefaciens with cassettes for gfp and bar expression. Transformation is essential to understand the role of genes during interaction between plants and its pathogens. Using a binary plasmid vector based in the pPZP201BK, both germinated conidia and physically fragmented hyphae of G. citricarpa were transformed. Eight independent transformants of G. citricarpa resistant to ammonium glifosinate displayed GFP fluorescence. The majority (93.75%) of the G. citricarpa transformants was mitotically stable and contained a single T-DNA copy ectopically integrated to the chromosome. This is the first report of G. citricarpa transformation and will allow future work on virulence determinants of the fungus and possibly its control.

Endochitinase CHI2 of the biocontrol fungus Metarhizium anisopliae affects its virulence toward the cotton stainer bug Dysdercus peruvianus

Chitinases have been implicated in fungal cell wall remodeling and play a role in exogenous chitin degradation for nutrition and competition. Due to the diversity of these enzymes, assigning particular functions to each chitinase is still ongoing. The entomopathogenic fungus Metarhizium anisopliae produces several chitinases, and here, we evaluate whether endochitinase CHI2 is involved in the pathogenicity of this fungus. We constructed strains either overexpressing or lacking the CHI2 chitinase. These constructs were validated by Southern, Northern and Western blot analysis, and chitinase production. To access the effects of CHI2 chitinase in virulence, the cotton stainer bug Dysdercus peruvianus was used as a host. CHI2 overexpression constructs showed higher efficiency in host killing suggesting that the production of this chitinase by a constitutive promoter reduces the time necessary to kill the insect. More significantly, the knock out constructs showed decreased virulence to the insects as compared to the wild type strain. The lack of this single CHI2 chitinase diminished fungal infection efficiency, but not any other detectable trait, showing that the M. anisopliae family 18, subgroup B endochitinase CHI2 plays a role in insect infection.

Gene inactivation mediated by Agrobacterium tumefaciens in the filamentous fungi Metarhizium anisopliae

The list of fungal species with known complete genome and/or expressed sequence tag collections is extending rapidly during the last couple of years. Postgenomic gene function assignment is an obvious follow-up and depends on methodologies to test gene function in vivo. One of such methods is the generation of null mutants via homologous recombination at the wild-type loci by using inactivation cassettes. In this paper, the ability of Agrobacterium tumefaciens to genetically transform filamentous fungi was exploited to drive homologous recombination at the trp1 locus of the enthomopathogenic fungus Metarhizium anisopliae. The trp1 disruptants exhibited a clearly distinguishable phenotype from wild-type cells and were recovered with high efficiency of homologous recombination (22%). The complementation of such mutants with the wild-type gene generates only transformants with homologous integration.

Isolation, characterization, and transcriptional analysis of the chitinase chi2 Gene (DQ011663) from the biocontrol fungus Metarhizium anisopliae var. anisopliae

Metarhizium anisopliae infects arthropods via a combination of specialized structures and cuticle degradation. Hydrolytic enzymes are accepted as key factors for the host penetration step and include chitinases. The characterization of the chi2 chitinase gene from M. anisopliae var. anisopliae is reported. The chi2 gene is interrupted by two short introns and is 1,542-bp long, coding a predicted protein of 419 amino acids with a stretch of 19 amino acid residues displaying characteristics of signal peptide. The predicted chitinase molecular mass is 44 kDa with a mature protein of 42 kDa and a theoretical pI of 4.8. The comparison of the CHI2 predicted protein to fungal orthologues revealed similarity to the glycohydrolase family 18 and a phylogenetic analysis was conducted. The chi2 gene is up-regulated by chitin as a carbon source and in conditions of fungus autolysis, and is down-regulated by glucose. This regulation is consistent with the presence of putative CreA/Crel/Crr1 carbon catabolic repressor binding domains on the regulatory sequence.