Molecular cloning and characterization of 58 kDa chitinase gene fromSerratia marcescens KCTC 2172

A chitinase gene (pCHi58) encoding a 58 kDa chitinase was isolated from theSerratia marcescens KCTC 2172 cosmid library. The chitinase gene consisted of a 1686 bp open reading frame that encoded 562 amino acids.Escherichia coil harboring the pChi58 gene secreted a 58 kDa chitinase into the culture supernatant. The 58 kDa chitinase was purified using a chitin affinity column and mono-S column. A nucleotide andN-terminal amino acid sequence analysis showed that the 58 kDa chitinase had a leader peptide consisting of 23 amino acids which was cleaved prior to the 24th alanine. The 58 KDa chitinase exhibited a 98% similarity to that ofS. marcescens QMB 1466 in its nuclotide sequence. The chitinolytic patterns of the 58 kDa chitinase released N,N′-diacetyl chitobiose (NAG2) as the major hydrolysis end-product with a trace amount ofN-acetylglucosamine. When a 4-methylumbellyferyl-N-acetylglucosamin monomer, dimmer, and tetramer were used as substrates, the 58 kDa chitinase did not digest the 4-Mu-NAG monomer (analogue of NAG₂), thereby indicating that the 58 kDa chitinase was likely an endochitinase. The optimum reaction temperature and pH of the enzyme were 50°C and 5.0, respectively.     

Transgenic tobacco plants expressingBoRS1 gene fromBrassica oleracea var.acephala show enhanced tolerance to water stress

Water stress is by far the leading environmental stress limiting crop yields worldwide. Genetic engineering techniques hold great promise for developing crop cultivars with high tolerance to water stress. In this study, theBrassica oleracea var.acephala BoRS1 gene was transferred into tobacco throughAgrobacterium- mediated leaf disc transformation. The transgenic status and transgene expression of the transgenic plants was confirmed by polymerase chain reaction (PCR) analysis, Southern hybridization and semi-quantitative one step RT-PCR analysis respectively. Subsequently, the growth status under water stress, and physiological responses to water stress of transgenic tobacco were studied. The results showed that the transgenic plants exhibited better growth status under water stress condition compared to the untransformed control plants. In physiological assessment of water tolerance, transgenic plants showed more dry matter accumulation and maintained significantly higher levels of leaf chlorophyll content along with increasing levels of water stress than the untransformed control plants. This study shows thatBoRS1 is a candidate gene in the engineering of crops for enhanced water stress tolerance.     

Fungitoxicity of some higher plants againstRhizoctonia solani

Summary Leaves ofChenopodium ambrosioides exhibited strong fungitoxicity against the mycelial growth ofRhizoctonia solani causing damping off diseases of some seedlings. Minimum inhibitory concentration of the fungitoxic constituent isolated in form of essential oil, was found to be 1000 ppm at which it was fungicidal in nature. It exhibited broad range of antifungal activity and did not show any phytotoxicity on the germination and seedling growth ofPhaseolus aureus.     

The Saccharomyces cerevisiae chitinase,encoded by the CTS1-2 gene,confers antifungal activity against Botrytis cinerea to Transgenic tobacco

The Saccharomyces cerevisiae chitinase, encoded by the CTS1-2 gene has recently been confirmed by in vitro tests to possess antifungal abilities. In this study, the CTS1-2 gene has been evaluated for its in planta antifungal activity by constitutive overexpression in tobacco plants to assess its potential to increase the plant's defence against fungal pathogens. Transgenic tobacco plants, generated by Agrobacterium-mediated transformation, showed stable integration and inheritance of the transgene. Northern blot analyses conducted on the transgenic tobacco plants confirmed transgene expression. Leaf extracts from the transgenic lines inhibited Botrytis cinerea spore germination and hyphal growth by up to 70% in a quantitative in vitro assay, leading to severe physical damage on the hyphae. Several of the F₁ progeny lines were challenged with the fungal pathogen, B. cinerea, in a detached leaf infection assay, showing a decrease in susceptibility ranging from 50 to 70%. The plant lines that showed increased disease tolerance were also shown to have higher chitinase activities.     

The sequence of a pea vicilin gene and its expression in transgenic tobacco plants

A 5.5 kb Eco RI fragment containing a vicilin gene was selected from a Pisum sativum genomic library, and the protein-coding region and adjacent 5 and 3 regions were sequenced. A DNA construction comprising this 5.5 kb fragment together with a gene for neomycin phosphotransferase II was stably introduced into tobacco using an Agrobacterium tumefaciens binary vector, and the fidelity of expression of the pea vicilin gene in its new host was studied. The seeds of eight transgenic tobacco plants showed a sixteen-fold range in the level of accumulated pea vicilin. The level of accumulation of vicilin protein and mRNA correlated with the number of integrated copies of the vicilin gene. Pea vicilin was confined to the seeds of transgenic tobacco. Using immunogold labelling, vicilin was detected in protein bodies of eight out of ten embryos (axes plus cotyledons) and, at a much lower level, in two out of eleven endosperms. Pea vicilin was synthesized early in tobacco seed development; some molecules were cleaved as is the case in pea seeds, yielding a major parental component of M _r50000 together with a range of smaller polypeptides.     

Transgenic tobacco plants regenerated from leaf disks can be periclinal chimeras

Amongst rolC transgenic tobacco plants regenerated from leaf disks 6.5% are periclinal chimeras, i.e. plants with genetically different cell populations in different cell layers. The expression of the rolC gene of Agrobacterium rhizogenes causes a reduction in pigment content in leaves. The chimeric composition of the regenerated plants becomes thus apparent as light green leaf tissue in the transgenic region, tissue flanked by dark green wild-type sectors. Southern and northern blot analysis confirmed the chimeric nature of such plants. Investigation of selfed progeny of chimeric plants on selective media indicates that layer invasion in reproductive tissues can occur in tobacco early during the formation of the flower buds. The results show (1) that tobacco plants regenerated from leaf disks and grown on selective media have not necessarily the same clonal origin and (2) that they can give rise to non-transgenic offspring. The chimeric plants provide insight on the effect of rolC gene expression on microsporogenesis.     

Transgenic tobacco plants overexpressing the Met25 gene of Saccharomyces cerevisiae exhibit enhanced levels of cysteine and glutathione and increased tolerance to oxidative stress

Summary. The cysteine biosynthesis pathway differs between plants and the yeast Saccharomyces cerevisiae. The yeast MET25 gene encoded to O-acetylhomoserine sulfhydrylase (AHS) catalyzed the reaction that form homocysteine, which later can be converted into cystiene. In vitro studies show that this enzyme possesses also the activity of O-acetyl(thiol)lyase (OASTL) that catalyzes synthesis of cysteine in plants. In this study, we generated transgenic tobacco plants expressing the yeast MET25 gene under the control of a constitutive promoter and targeted the yeast protein to the cytosol or to the chloroplasts. Both sets of transgenic plants were taller and greener than wild-type plants. Addition of SO₂, the substrate of the yeast enzyme caused a significant elevation of the glutathione content in representative plants from each of the two sets of transgenic plants expressing the yeast gene. Determination of non-protein thiol content indicated up to four-folds higher cysteine and 2.5-fold glutathione levels in these plants. In addition, the leaf discs of the transgenic plants were more tolerant to toxic levels of sulphite, and to paraquat, an herbicide generating active oxygen species.     

Disease cycle involved in damping-off of groundnut caused byRhizoctonia solani

Summary By taking into consideration of the results of various studies on damping-off of groundnut caused byRhizoctonia solani, the mechanisms leading to ultimate collapse and death of the seedlings, are described.     

Enzyme Production by the Mycoparasite Verticillium biguttatum against Rhizoctonia solani

Verticillium biguttatum, a mycoparasite of the ubiquitous soil-borne plant pathogen Rhizoctonia solani, excreted chitinase and beta-1,3-glucanase into liquid medium when grown on laminarin and chitin, respectively. Neither chitinase nor beta-1,3-glucanase was produced by the mycoparasite when grown on cell walls of two isolates of R. solani representing anastomosis groups (AG)-3 and AG-8. Extracellular protease was induced by growth on cell walls of the pathogen, whereas beta-1,3-glucanase and chitinase were produced bound to the cell wall of V. biguttatum. This is the first report of chitinase, beta-1,3-glucanase and protease production by V. biguttatum. These enzymes may play a previously unforeseen role in dissolving and penetrating the cell walls of R. solani.     

Transgenic tobacco plants expressing PicW gene from Picea wilsonii exhibit enhanced freezing tolerance

A cold-induced gene of 669 bp in length without introns, PicW, was cloned from Picea. wilsonii, a cold tolerant conifer species. Sequence analysis showed that it was a member of the dehydrin family because of its conserved amino acid constitution and protein secondary structure. The protein was rich in hydrophilic amino acids such as alanine, lysine, glutamic acid, glutamine and threonine, but devoid of two hydrophobic amino acids, cysteine and tryptophan. The PicW gene contained five repeated motifs homologous to the core K-segment in dehydrins. Protein secondary structure prediction showed that PicW comprised 29 % α-helix, mostly in the K-homologous segment, and random coils. The PicW gene was cloned into the expression vector PEZR(K)-LC under the 35S promoter and transformed into tobacco plants. After treatment at ?5 °C for 3 h, all of the tobacco plants were wilting. However, the transgenic plants showed better growth performance than wild-type plants. Further tests of physiological indexes including relative electrolyte leakage and malondialdehyde content, proline and soluble sugar content also revealed significant differences between the wild-type and transgenic tobacco plants. It was concluded that the PicW gene could be an important gene resource for freezing-tolerant plant breeding.     

Grouping of isolates in AG 2 ofRhizoctonia solani by total cellular fatty acid analysis

Total-cellular fatty acid compositions of 34 isolates ofRhizoctonia solani belonging to intraspecific groups (ISGs) of anastomosis group (AG) 2, i.e., AG 2-1, AG 2-2 IIIB (mat rush), AG 2-2 IV (sugar beet), AG 2-2 LP (turfgrass), and AG 2–3 (soybean), were compared. The major fatty acids identified were palmitic, stearic, and oleic acids. Principal component analysis based on the percentage composition of total cellular fatty acids revealed consistently low variability among isolates of a single ISG of AG 2. Average linkage cluster analysis showed that isolates obtained from turfgrass representing a newly proposed group, AG 2-2 LP, were differentiated from other AG 2 ISGs. Isolates of another newly proposed group AG 2–3, from diseased soybean were also closely related to AG 2-1 and AG 2-2 IIIB but distinguishable from the AG 2-1 and AG 2-2 LP isolates by the average linkage cluster analysis. These results suggested that the percentage composition of total-cellular fatty acids is a distinct characteristic for the five ISGs belonging to AG 2, and fatty acid analysis is useful for the differentiation and characterization of these ISGs of AG 2 inR. solani.     

RFLP analysis of the PCR-amplified 28S rDNA inRhizoctonia solani

RFLP analyses of a portion of the 28S rDNA gene region were conducted by using four restriction endonucleases for 57 isolates of 13 intraspecific groups (ISGs) representing 7 anastomosis groups (AGs) ofRhizoctonia solani. Variations in the PCR-amplified rDNA products and the polymorphisms on digestion with restriction enzymes (BamHI,HaeIII,HhaI andHpaII) were observed among three AGs, AG 1, 2 and 4. These differences were also conserved among some ISGs of AG 1 and AG 2. Among ISGs of AG 1, the pattern of rDNA fragments of AG 1-IA obtained by digestion withHpaII was significantly different from those of AG 1-IB and IC. Such difference in the fragment pattern was also observed among AG 2-1, 2-2 IIIB and 2-2 IV by the digestion withHhaI andHpaII. A dendrogram derived from the restriction enzyme data showed that ISGs from AG 1 and AG 2 can each be subdivided into distinct groups, those are distantly related to the majority isolates of the other AGs.     

Impact of two soil-applied herbicides on damping-off of cowpea caused byRhizoctonia solani

Summary Alachlor was more inhibitory toRhizoctonia solani growth than fluchloralin in potato dextrose broth (PDB). Infective capacity of the pathogen was not altered by growing it in a medium containing either of the herbicides. Cowpea seedlings grown in alachlor-treated soil were more susceptible toR. solani than those treated with fluchloralin and the untreated seedlings. Pre-sowing application of alachlor in soil (5 l a.i./kg) aggravated damping-off whereas fluchloralin decreased the disease incidence to nearly half of that in untreated soil in greenhouse pot tests (av. temperature 31±5°C). Both herbicides reduced damping-off in pots kept at constant temperature of 30°C and increased the disease incidence at 20°C. Fungus growth in culture was stimulated at 20° but was strongly inhibited at 30°C by both herbicides. Growth inhibition by herbicides was maximum in PDB of pH 8 and decreased steadily up to pH 5.Impact of fluchloralin and alachlor onR. solani damping-off of cowpea appears to be due to the predisposing effect by the herbicides on the susceptibility of the host and is influenced by atmospheric temperature.     

Transgenic tobacco and peanut plants expressing a mustard defensin show resistance to fungal pathogens

Defensins are small positively charged, antimicrobial peptides (~5 kDa in size) and some of them exhibit potent antifungal activity. We have cloned the complete cDNA containing an ORF of 243 bp of a defensin of mustard. The deduced amino acid sequence of the peptide showed more than 90% identity to the amino acid sequence of the well-characterized defensins, RsAFP-1 and RsAFP-2 of Raphanus sativus. We have generated and characterized transgenic tobacco and peanut plants constitutively expressing the mustard defensin. Transgenic tobacco plants were resistant to the fungal pathogens, Fusarium moniliforme and Phytophthora parasitica pv. nicotianae. Transgenic peanut plants showed enhanced resistance against the pathogens, Pheaoisariopsis personata and Cercospora arachidicola, which jointly cause serious late leaf spot disease. These observations indicate that the mustard defensin gene can be deployed for deriving fungal disease resistance in transgenic crops.     

Expression of a CaMV::sak-gusA-mgfp gene in tobacco plants

A gene encoding staphylokinase from Staphylococcus aureus was cloned into the plant transformation binary vector pCAMBIA1303. The presence of a CaMV::sak-gusA-mgfp gene in Agrobacterium was confirmed by polymerase chain reaction PCR. Tobacco seedlings were used as explants for Agrobacterium tumefaciens-mediated transformation with the pCAMBIA1303sak vector carrying the fusion gene construct CaMV::sak-gusA-mgfp and the expression of the fusion gene was identified in Nicotiana tabacum plants by β-glucuronidas assay. This revised version was published online in August 2006 with corrections to the Cover Date.