HYD3, a conidial hydrophobin of the fungal entomopathogen Metarhizium acridum induces the immunity of its specialist host locust.

Conidial hydrophobins in fungal pathogens of plants, insects, and humans are required for fungal attachment and are associated with high virulence. They are believed to contribute to the pathogenesis of infection by preventing immune recognition. Here, we refute this generalisation offering a more nuanced analysis. We show that MacHYD3, a hydrophobin located on the conidial surface of the specialist entomopathogenic fungus Metarhizium acridum (narrow host range, kills only locusts and grasshoppers), activates specifically the humoral and cellular immunity of its own host insect, Locusta migratoria manilensis (Meyen) but not that of other non-host insects. When topically applied to the cuticle, purified MacHYD3 improved the resistance of locusts to both specialist and generalist fungal pathogens (wide host range) but had no effect on the fungal resistance of other insects, including Spodoptera frugiperda and Galleria mellonella. Hydrophobins extracted from the generalist fungal pathogens M. anisopliae and Beauveria bassiana had no effect on the resistance of locusts to fungal infection. Thus, the host locust has evolved to recognize the conidial hydrophobin of its specialist fungal pathogen, whereas conidial hydrophobins from generalist fungi are able to evade recognition. Our results distinguish the immunogenic potential of conidial hydrophobins between specialist and generalist fungi.

MaHog1, a Hog1-type mitogen-activated protein kinase gene, contributes to stress tolerance and virulence of the entomopathogenic fungus Metarhizium acridum.

Fungal biocontrol agents have great potential in integrated pest management. However, poor efficacy and sensitivity to various adverse factors have hampered their wide application. In eukaryotic cells, Hog1 kinase plays a critical role in stress responses. In this study, MaHog1 (GenBank accession no. EFY85878), encoding a member of the Hog1/Sty1/p38 mitogen-activated protein kinase family in Metarhizium (Me.) acridum, was identified. Targeted gene disruption was used to analyse the role of MaHog1 in virulence and tolerance of adverse factors. Mutants with MaHog1 depletion showed increased sensitivity to high osmotic stress, high temperature and oxidative stress, and exhibited remarkable resistance to cell wall-disturbing agents. These results suggest that Hog1 kinase has a conserved function in regulating multistress responses among fungi, and that MaHog1 might influence cell wall biogenesis in Me. acridum. Bioassays conducted with topical inoculation and intrahaemocoel injection revealed that MaHog1 is required for both penetration and postpenetration development of Me. acridum. MaHog1 disruption resulted in a significant reduction in virulence, likely due to the combination of a decrease in conidial germination, a reduction in appressorium formation and a decline in growth rate in insect haemolymph, which might be caused by impairing fungal tolerance of various stresses during infection.

Two hydrophobins are involved in fungal spore coat rodlet layer assembly and each play distinct roles in surface interactions, development and pathogenesis in the entomopathogenic fungus, Beauveria bassiana.

The entomogenous filamentous fungus, Beauveria bassiana expresses two hydrophobin genes, hyd1 and hyd2, hypothesized to be involved in cell surface hydrophobicity, adhesion, virulence, and to constitute the protective spore coat structure known as the rodlet layer. Targeted gene inactivation of hyd1 resulted in seemingly 'bald' conidia that contained significantly altered surface fascicles or bundles. These cells displayed decreased spore hydrophobicity, loss of water mediated dispersal, changes in surface carbohydrate epitopes and ß-1,3-glucan distribution, lowered virulence in insect bioassays, but no effect on adhesion. In contrast, Δhyd2 mutants retained distorted surface bundles, but truncated/incomplete rodlets could be seen within the bundles. Δhyd2 conidia displayed both decreased cell surface hydrophobicity and adhesion, but the mutant was unaffected in virulence. The double Δhyd1Δhyd2 mutant was distinct from the single mutants, lacking both bundles and rodlets, and displaying additively decreased cell surface hydrophobicity, reduced cell attachment and lowered virulence than the Δhyd1 mutant. Epitope tagged constructs of the proteins were used to examine the expression and distribution of the proteins and to demonstrate the continued presence of Hyd2 in the Δhyd1 strain and vice versa. The implications of our results with respect to fascicle and rodlet assembly on the spore surface are discussed.

Sulfonylurea resistance as a new selectable marker for the entomopathogenic fungus Beauveria bassiana.

Beauveria bassiana is a filamentous ascomycete that is pathogenic towards a broad host range of insect targets and is increasingly serving as a model for examining fungal development and host-pathogen interactions. B. bassiana displays a prohibitive level of resistance against many current fungal and/or yeast selection markers including hygromycin, neomycin, and zeocin. A genetic transformation system for B. bassiana based upon the use of a sulfonylurea resistance cassette derived from the Magnaporthe grisea, acetolactate synthase gene (sur) was developed. The transformation frequency ranged from 100-150 transformants per microgram DNA/10(8) cells and Southern blot analysis indicated that the plasmid vector was randomly integrated into the genome of B. bassiana. In addition, a construct bearing the sur gene and the enhanced green fluorescent protein gene egfp as a visual marker was used to successfully transform B. bassiana. Over 95% of the transformants retained the sulfonylurea resistance phenotype under non-selective conditions. The described transformation method increases opportunities for the genetic manipulation of B. bassiana.

Isolation of single chain variable fragments against six esters of pyrethrins by subtractive phage display.

Recombinant antibodies (rAbs) are a new diagnostic test for immulogical detection. To date, there are no reports about anti-pyrethrins rAbs. Here we describe the generation of monomeric and dimeric single chain variable fragments (scFvs) with affinity for six esters of pyrethrins using a subtractive phage display technology. First, scFv libraries with long-linker (Ger(4)Ser)(3) and short-linker (Ger(4)Ser) were established to contain 1.04 x 10(7) or 6.07 x 10(6) transformants. After four rounds of panning, phage ELISA demonstrated that three clones (E2, F2, and H7) showed higher affinity from the long-linker library, and clones (h6, a5) exhibited better antibody activity to pyrethrin I and II from the short-linker library. The scFv candidates were sequenced to identify the specific antibody response against pyrethrins. Isolated scFvs constitute valuable tools for real-time detection of pyrethrins. In addition, the subtractive phage display provides a simple approach for isolation of scFvs.

[Selection of differential DNA fragment of Tilletia controversa Kühn and establishment of molecular detection approach].

A reliable and simple polymerase chain reaction method for TCK pathogen was established firstly. A 1322bp unique fragment of TCK was amplified and identified by the technique of semi-specific random amplified polymorphism (RM-PCR). Two pairs of species-specific primers CQUK2/CQUK3 and CQUK4/CQUK5 were designed according to the unique fragment of TCK. The first pair primers were capable to stably amplify target DNA band of 747bp from chromosomal DNA of 18 strains of TCK isolates without any DNA bands obtained from 29 strains of TCT. The second pair primers could produce a 200bp target DNA band stably, while no band was amplified from teliospore or mycelium DNA of TCT of strains. Tilletia genus primers were used as internal control of molecular detection system, which can detect whether the PCR inhibitors exist in testing sample or avoid pseudo-negative and pseudo-positive of PCR reaction. The molecular detection approach could rapidly, accurately detect and identify the DNA of teliospore or mycelium of TCK from wheat tissues.

Construction of cDNA library of cotton mutant Xiangmian-18 library during gland forming stage.

Gossypol, a secondary metabolite stored in the glands of cotton, protecting cottonseed from consumption of human and monogastric animal. This ability is unique to the tribe Gossypieae. Although the relationship between gossypol and pigment gland has been studied for a long time, the development mechanism of pigment gland has not been investigated at molecular level. Here we described a simple and efficient method for constructing a normalized cDNA library from a cotton mutant, Xiangmian-18, during its pigments gland forming stage. It combined switching mechanism at 5'-end of RNA transcript (SMART) technique and duplex-specific nuclease (DSN) normalization methods. In a model experiment, double-stranded cDNAs were synthesized from mRNAs, processed by normalization and Sfi I restriction endonuclease, and finally the cDNAs were ligated to pDNR-LIB vector. The ligation mixture was transformed into E. coli JM109 by electroporation. Counting the number of colonies, the titer of the original library was 5.86x10(5)cfu/ml in this library. Electrophoresis gel results indicated the fragments ranged from 800bp to 2kb, with the average size of 1400bp. Random picking clones showed that the recombination rate was 94%. The results showed that the cDNA library constructed successfully was a full-length library with high quality, and could be used to screen the genes related to development of pigments gland cottons.

[High efficient expression and bio-activity assay of recombinant antibody for citrus bacterial canker disease].

Citrus bacterial canker disease caused by the gram negative bacterium Xanthomonas axonopodis pv. citri (XAC) is a severe bacterial disease of most commercial citrus species and cultivars around the world. Single chain variable fragment (ScFv) is artificial construction small molecular antibody produced by genetic engineering which may be used to identify target pathogens and prevent plant diseases including XAC. To express ScFv against XAC and obtain functional ScFv, single-chain antibody fragments (ScFv 95) selected by ribosome display was amplified using an assembly of polymerase chain reaction (PCR), and a recombined plasmid pET30a( + )-XAC-ScFv was constructed by inserting the single chain Fv gene into bacterial expression vector pET30a( + ). PET30a( + )-XAC-ScFv was transformed into Escherichia coli BL21 (DE3) and expressed which was induced by IPTG. Products were purified though Ni-NTA His Bind resin. The collected antibodies were refolded by gel filtration chromatography, and activity assaying process was done. The results showed that ScFv recombined antibody of XAC with a molecular of 32kDa was expressed successfully as inclusion bodies and the functional ScFv was obtained through purification and renaturation. Meanwhile, the Biacore analysis indicates that XAC-ScFv-95 showed significant affinity to LPS of Xac, which paves a new way for immunization diagnosis and exploration of integrated control of citrus bacterial canker disease.

Role of hunchback in segment patterning of Locusta migratoria manilensis revealed by parental RNAi.

In long germ embryos, all body segments are specified simultaneously during the blastoderm stage. In contrast, in short germ embryos, only the anterior segments are specified during the blastoderm stage, leaving the rest of the body plan to be specified later. The striking embryological differences between short and long germ segmentation imply fundamental differences in patterning at the molecular level. To gain insights into the segmentation mechanisms of short germ insects, we have investigated the role of the homologue of the Drosophila gap gene hunchback (hb) in a short germ insect Locusta migratoria manilensi by paternal RNA interference (RNAi). Phenotypes resulting from hb knockdown were categorized into three classes based on severity. In the most extreme case, embryos developed the most anterior structures only, including the labrum, antennae and eyes. The following conclusions were drawn: (i) L. migratoria manilensis hb (Lmm'hb) controls germ band morphogenesis and segmentation in the anterior region; (ii) Lmm'hb may function as a gap gene in a wide domain including the entire gnathum and thorax; and (iii) Lmm'hb is required for proper growth of the posterior germ band. These findings suggest a more extensive role for L. migratoria manilensis hunchback in anterior patterning than those described in Drosophila.

[Cloning and characterization of the neutral trehalase gene in Metarhizium anisopliae CQMa102].

The partial fragment of the neutral trehalase (NTL) in Metarhizium anisopliae CQMa102 was amplified by the polymerase chain reaction (PCR) with primers designed according to the sequences of the NTL in GenBank. The amplified fragment was cloned and sequenced. Based on the known sequence of NTL gene, the 5' and 3' rapid amplification of cDNA ends (RACE) were used to amplify the 5' and 3'regions of the NTL cDNA, then the whole cDNA sequence of NTL gene in M. anisopliae CQMa102 was obtained by combining the above sequences and its whole genomic DNA was amplified by PCR. In order to obtain more regulatory information of the NTL, panhandle polymerase chain reaction strategy was used to amplify the 5' flanking sequences adjacent to the known sequence of the neutral trehalase gene. The sequence analysis shows that the DNA sequence is 3484bp in size, includes three introns, and the cDNA sequence is 2385 bp in size, encodes a protein of 737 amino acid residues with a calculated Mr of 83.1kD, in which there is a cyclic adenosine 3', 5'-monophosphate-dependent phosphorylation consensus site and a putative calcium binding site, which is consistent with a regulatory enzyme. Comparison of this sequence with the NTL of M. anisopliae ME1 in GenBank (GenBank Accession: AJ298019, AJ298020) shows that the nucleotide homology is as high as 93%, and the amino acid homology comes up to 99%. Southern analysis indicated that NTL gene was present as a single copy in this M. anisopliae strain. A single transcript of approximately 2.5 kb was detected by Northern blot analysis. The NTL mRNA was present throughout spore germination in rich medium, but accumulated to its highest level at the early stage of exponential growth. Thereafter, the mRNA level declined at the late stage of exponential growth, but began to show an increase during the stationary phase of growth. A 982bp upstream sequence of NTL was amplified using panhandle PCR method, which contains one stress response element (STRE). The NTL nucleotide sequence and its amino acid sequence have been accessed by GenBank (Accession: AY557613, AY557612).