Cloning and overexpression of antifungal barley chitinase gene in Escherichia coli

Site-directed mutagenesis, heterologous expression of cyanamide hydratase gene and antimicrobial activity of cyanamide

Site-directed mutagenesis on a recombinant plasmid, pUC8, that contained the cah gene, was conducted and confirmed by sequence analysis. Single base substitution, G to A at nucleotide position 81 or T to C at nucleotide position 84 of cah gene does not change the amino acid sequence of cah enzyme but eliminates the HindIII site. The wild-type cah and its mutants were cloned and overexpressed in pQE-60 Escherichia coli expression system. Western blot analysis confirmed the production of 27.7-kDa cah enzyme by all the recombinants. The mutated cah gene devoid of HindIII site was used to generate a recombinant plant transformation vector (pCAMBIA-cah). Agrobacterium-mediated transformation was performed in Nicotiana tabaccum cv. Samsun plants by employing the leaf-disc method. The integration and expression of cah gene in transgenic plants were confirmed by polymerase chain reaction, Southern and Western blot analyses. Antimicrobial activity of cyanamide against phytopathogenic fungi and bacteria was determined. Cyanamide can be used as fertilizer as well as an antimicrobial salt against phytopathogenic fungi and bacteria. The present investigation reports the heterologous expression of the cah marker gene. Due to its innate ability to convert cyanamide to urea and the broad-spectrum antimicrobial activity of cyanamide, the cah gene can be used to facilitate plant growth promotion and biocontrol of phytopathogens.

Combined expression of chitinase and lipid transfer protein genes in transgenic carrot plants enhances resistance to foliar fungal pathogens

Two pathogenesis-related (PR) protein genes consisting of a barley chitinase (chi-2) and a wheat lipid-transfer-protein (ltp) were introduced singly and in combination into carrot plants via Agrobacterium-mediated transformation using the phosphinothricin acetyl transferase (bar) gene as a selectable marker. Over 75% of regenerated plants were confirmed to be positive for the transgenes by PCR and RT-PCR and were resistant to the herbicide Liberty (0.2%, v/v). Northern analysis and immunoblotting confirmed the expression of the transgenes in about 70% of the plants, with variable expression levels among individual lines. Southern analysis revealed from one to three copies of each transgene. Transgenic plants were inoculated with two necrotrophic foliar fungal pathogens, Alternaria radicicola and Botrytis cinerea, and showed significantly higher resistance when both PR genes were expressed compared to single-gene transformants. The level of disease reduction in plants expressing both genes was 95% for Botrytis and 90% for Alternaria infection compared to 40-50% for single-gene transformants. The chi2 and ltp genes could be deployed in combination in other crop plants to significantly enhance resistance to necrotrophic fungal pathogens.

Expression of a Beauveria bassiana chitinase (Bbchit1) in Escherichia coli and Pichia pastoris

Beauveria bassiana chitinase (Bbchit1) is an important cuticle degrading enzyme involved in pathogenesis of fungi against insect. To obtain enough active chitinase for performing in vitro functional analysis, Bbchit1 gene was expressed in Escherichia coli and Pichia pastoris, respectively. The high-level production of recombinant Bbchit1 was detected in E. coli expression system, however mainly located in inclusion bodies. Refolding of solubilized inclusion body proteins was achieved by dialysis. In P. pastoris expression system, Bbchit1 was secreted into the culture medium under the induction of methanol. Active Bbchit1 was purified to near 90% purity from culture medium by desalting chromatography and anion exchange chromatography. The yield of Bbchit1 produced by P. pastoris was estimated at 153 mg/L, significantly higher than that of the refolded Bbchit1 from E. coli inclusion bodies (50 mg/L). Additionally, the specific activity of Bbchit1 from P. pastoris was also higher than that from E. coli (3.9 U/mg versus 2.8 U/mg). These results indicated P. pastoris was a convenient expression system for the efficient production of Bbchit1.

Heterologous expression of new antifungal chitinase from wheat

Chitinases (EC 3.2.1.14) have been grouped into seven classes (class I-VII) on the basis of their structural properties. Chitinases expressed during plant-microbe interaction are involved in defense responses of host plant against pathogens. In the present investigation, chitinase gene from wheat has been subcloned and overexpressed in Escherichia coli BL-21 (DE3). Molecular phylogeny analyses of wheat chitinase indicated that it belongs to an acidic form of class VII chitinase (glycosyl hydrolase family 19) and shows 77% identity with other wheat chitinase of class IV and low level identity to other plant chitinases. The three-dimensional structural model of wheat chitinase showed the presence of 10 alpha-helices, 3 beta-strands, 21 loop turns and the presence of 6 cysteine residues that are responsible for the formation of 3 disulphide bridges. The active site residues (Glu94 and Glu103) may be suggested for its antifungal activity. Expression of chitinase (33 kDa) was confirmed by SDS-PAGE and Western hybridization analyses. The yield of purified chitinase was 20 mg/L with chitinase activity of 1.9 U/mg. Purified chitinase exerted a broad-spectrum antifungal activity against Colletotrichum falcatum (red rot of sugarcane) Pestalotia theae (leaf spot of tea), Rhizoctonia solani (sheath blight of rice), Sarocladium oryzae (sheath rot of rice) Alternaria sp. (grain discoloration of rice) and Fusarium sp. (scab of rye). Due to its innate antifungal potential wheat chitinase can be used to enhance fungal-resistance in crop plants.