Over expression of rice chitinase gene in transgenic peanut (Arachis hypogaea L.) improves resistance against leaf spot

BpAFP, a Broussonetia papyrifera latex chitinase, exhibits a dual role in resisting to both Verticillium wilt disease and lepidopterous pests, Plutella xylostella and Prodenia litura

Paper mulberry (Broussonetia papyrifera) is a fast-growing tree known for its tolerance to diverse biotic and abiotic stresses. To explore genes combating Verticillium wilt, a devasting and formidable disease damage to cotton and many economically significant crops, we purified an antifungal protein, named BpAFP, from the latex of paper mulberry. Based on peptide fingerprint, we cloned the full cDNA sequence of BpAFP and revealed that BpAFP belongs to Class I chitinases, sharing 74 % identity with B. papyrifera leaf chitinase, PMAPII. We further introduced BpAFP into Arabidopsis, tobacco, and cotton. Transgenic plants exhibited significant resistance to Verticillium wilt. Importantly, BpAFP also demonstrated insecticidal activity against herbivorous pests, Plutella xylostella, and Prodenia litura, when feeding the larvae with transgenic leaves. Our finding unveils a dual role of BpAFP in conferring resistance to both plant diseases and lepidopterous pests.

Co-overexpression of chitinase and β-1,3-glucanase significantly enhanced the resistance of Iranian wheat cultivars to Fusarium

Fusarium head blight (FHB) is a devastating fungal disease affecting different cereals, particularly wheat, and poses a serious threat to global wheat production. Chitinases and β-glucanases are two important proteins involved in lysing fungal cell walls by targeting essential macromolecular components, including chitin and β-glucan micro fibrils. In our experiment, a transgenic wheat (Triticum aestivum) was generated by introducing chitinase and glucanase genes using Biolistic technique and Recombinant pBI121 plasmid (pBI-ChiGlu (-)). This plasmid contained chitinase and glucanase genes as well as nptII gene as a selectable marker. The expression of chitinase and glucanase was individually controlled by CaMV35S promoter and Nos terminator. Immature embryo explants from five Iranian cultivars (Arta, Moghan, Sisun, Gascogen and A-Line) were excised from seeds and cultured on callus induction medium to generate embryonic calluses. Embryogenic calluses with light cream color and brittle texture were selected and bombarded using gold nanoparticles coated with the recombinant pBI-ChiGlu plasmid. Bombarded calluses initially were transferred to selective callus induction medium, and later, they were transfferd to selective regeneration medium. The selective agent was kanamycin at a concentration of 25 mg/l in both media. Among five studied cultivars, A-Line showed the highest transformation percentage (4.8%), followed by the Sisun, Gascogen and Arta in descending order. PCR and Southern blot analysis confirmed the integration of genes into the genome of wheat cultivars. Furthermore, in an in-vitro assay, the growth of Fusarium graminearum was significantly inhibited by using 200 μg of leaf protein extract from transgenic plants. According to our results, the transgenic plants (T1) showed the resistance against Fusarium when were compared to the non-transgenic plants. All transgenic plants showed normal fertility and no abnormal response was observed in their growth and development.

Multifaceted roles of plant glycosyl hydrolases during pathogen infections: more to discover

MAIN CONCLUSION

Carbohydrates are hydrolyzed by a family of carbohydrate-active enzymes (CAZymes) called glycosidases or glycosyl hydrolases. Here, we have summarized the roles of various plant defense glycosidases that possess different substrate specificities. We have also highlighted the open questions in this research field. Glycosidases or glycosyl hydrolases (GHs) are a family of carbohydrate-active enzymes (CAZymes) that hydrolyze glycosidic bonds in carbohydrates and glycoconjugates. Compared to those of all other sequenced organisms, plant genomes contain a remarkable diversity of glycosidases. Plant glycosidases exhibit activities on various substrates and have been shown to play important roles during pathogen infections. Plant glycosidases from different GH families have been shown to act upon pathogen components, host cell walls, host apoplastic sugars, host secondary metabolites, and host N-glycans to mediate immunity against invading pathogens. We could classify the activities of these plant defense GHs under eleven different mechanisms through which they operate during pathogen infections. Here, we have provided comprehensive information on the catalytic activities, GH family classification, subcellular localization, domain structure, functional roles, and microbial strategies to regulate the activities of defense-related plant GHs. We have also emphasized the research gaps and potential investigations needed to advance this topic of research.

Characterization of soybean chitinase genes induced by rhizobacteria involved in the defense against Fusarium oxysporum

Rhizobacteria are capable of inducing defense responses via the expression of pathogenesis-related proteins (PR-proteins) such as chitinases, and many studies have validated the functions of plant chitinases in defense responses. Soybean (Glycine max) is an economically important crop worldwide, but the functional validation of soybean chitinase in defense responses remains limited. In this study, genome-wide characterization of soybean chitinases was conducted, and the defense contribution of three chitinases (GmChi01, GmChi02, or GmChi16) was validated in Arabidopsis transgenic lines against the soil-borne pathogen Fusarium oxysporum. Compared to the Arabidopsis Col-0 and empty vector controls, the transgenic lines with GmChi02 or GmChi16 exhibited fewer chlorosis symptoms and wilting. While GmChi02 and GmChi16 enhanced defense to F. oxysporum, GmChi02 was the only one significantly induced by Burkholderia ambifaria. The observation indicated that plant chitinases may be induced by different rhizobacteria for defense responses. The survey of 37 soybean chitinase gene expressions in response to six rhizobacteria observed diverse inducibility, where only 10 genes were significantly upregulated by at least one rhizobacterium and 9 genes did not respond to any of the rhizobacteria. Motif analysis on soybean promoters further identified not only consensus but also rhizobacterium-specific transcription factor-binding sites for the inducible chitinase genes. Collectively, these results confirmed the involvement of GmChi02 and GmChi16 in defense enhancement and highlighted the diverse inducibility of 37 soybean chitinases encountering F. oxysporum and six rhizobacteria.

Cloning of maize chitinase 1 gene and its expression in genetically transformed rice to confer resistance against rice blast caused by Pyricularia oryzae

Fungal pathogens are one of the major reasons for biotic stress on rice (Oryza sativa L.), causing severe productivity losses every year. Breeding for host resistance is a mainstay of rice disease management, but conventional development of commercial resistant varieties is often slow. In contrast, the development of disease resistance by targeted genome manipulation has the potential to deliver resistant varieties more rapidly. The present study reports the first cloning of a synthetic maize chitinase 1 gene and its insertion in rice cv. (Basmati 385) via Agrobacterium-mediated transformation to confer resistance to the rice blast pathogen, Pyricularia oryzae. Several factors for transformation were optimized; we found that 4-week-old calli and an infection time of 15 minutes with Agrobacterium before colonization on co-cultivation media were the best-suited conditions. Moreover, 300 μM of acetosyringone in co-cultivation media for two days was exceptional in achieving the highest callus transformation frequency. Transgenic lines were analyzed using molecular and functional techniques. Successful integration of the gene into rice lines was confirmed by polymerase chain reaction with primer sets specific to chitinase and hpt genes. Furthermore, real-time PCR analysis of transformants indicated a strong association between transgene expression and elevated levels of resistance to rice blast. Functional validation of the integrated gene was performed by a detached leaf bioassay, which validated the efficacy of chitinase-mediated resistance in all transgenic Basmati 385 plants with variable levels of enhanced resistance against the P. oryzae. We concluded that overexpression of the maize chitinase 1 gene in Basmati 385 improved resistance against the pathogen. These findings will add new options to resistant germplasm resources for disease resistance breeding. The maize chitinase 1 gene demonstrated potential for genetic improvement of rice varieties against biotic stresses in future transformation programs.

Overexpression of chitinase in the endophyte Phomopsis liquidambaris enhances wheat resistance to Fusarium graminearum

Fusarium head blight (FHB) is a disease that affects wheat crops worldwide and is caused by Fusarium graminearum. Effective and safe strategies for the prevention and treatment of the disease are very limited. Phomopsis liquidambaris, a universal endophyte, can colonize wheat. Two engineered strains, Phomopsis liquidambaris OE-Chi and IN-Chi, were constructed by transformation with a plasmid and integration of a chitinase into the genome, respectively. The OE-Chi and IN-Chi strains could inhibit the expansion of Fusarium sp. in plate confrontation assays in vitro. Colonization of the OE-Chi strain in wheat showed better effects than colonization of the IN-Chi strain and alleviated the inhibition of wheat growth caused by F. graminearum. The shoot length, root length and fresh weight of infected wheat increased by 164.9%, 115.4%, and 190.7%, respectively, when the plants were inoculated with the OE-Chi strain. The peroxidase (POD) activity in the wheat root increased by 38.0%, and it was maintained at a high level in the shoot, which suggested that the OE-Chi strain could enhance the resistance of wheat to F. graminearum. The root and shoot superoxide dismutase (SOD) activities were decreased by 11.8% and 19.0%, respectively, which may be helpful for colonization by the OE-Chi strain. These results suggested that the Phomopsis liquidambaris OE-Chi strain may be a potential endophyte in the biocontrol of FHB.

Expression of Drosera rotundifolia Chitinase in Transgenic Tobacco Plants Enhanced Their Antifungal Potential

In this study, a chitinase gene (DrChit) that plays a role in the carnivorous processes of Drosera rotundifolia L. was isolated from genomic DNA, linked to a double CaMV35S promoter and nos terminator in a pBinPlus plant binary vector, and used for Agrobacterium-mediated transformation of tobacco. RT-qPCR revealed that within 14 transgenic lines analysed in detail, 57% had DrChit transcript abundance comparable to or lower than level of a reference actin gene transcript. In contrast, the transgenic lines 9 and 14 exhibited 72 and 152 times higher expression level than actin. The protein extracts of these two lines exhibited five and eight times higher chitinolytic activity than non-transgenic controls when measured in a fluorimetric assay with FITC-chitin. Finally, the growth of Trichoderma viride was obviously suppressed when the pathogen was exposed to 100 μg of crude protein extract isolated from line 9 and line 14, with the area of mycelium growth reaching only 56.4% and 45.2%, of non-transgenic control, respectively. This is the first time a chitinase from a carnivorous plant with substrate specificity for long chitin polymers was tested in a transgenic plant with the aim of exploring its antifungal potential.

Lack of efficacy of transgenic pea (Pisum sativum L.) stably expressing antifungal genes against Fusarium spp. in three years of confined field trials

Fusarium root rot is a major pea disease in Canada and only partial tolerance exists in germplasm. Transgenic technologies may hold promise but the economic benefits of genetically modified (GM) pea will need to surpass the regulatory costs, time and labor involved in bringing a GM crop to market. European pea (Pisum sativum L.) cultivars expressing four antifungal genes, 1-3 β glucanase (G), endochitinase (C) (belonging to PR proteins family), polygalacturonase inhibiting proteins (PGIPs) (P) and stilbene synthase (V) have been transformed for disease tolerance and showed disease tolerance under laboratory conditions. Transgenic lines with four antifungal genes inserted either individually or stacked through crossing were tested for their efficacy against Fusarium root rot (Fusarium avenaceum) in confined trials over three years (2013 to 2015) in comparison with two parental German lines and three Canadian lines. Superior emergence, higher fresh weight or lower disease ratings above and below ground, of transgenic lines in presence of disease inoculum were not observed consistently in the three years of field experiments when compared to the parental and Canadian lines in the presence of disease inoculum. No indication of an advantage of stacked genes over single genes was observed. Most transgenic lines had lower relative gene expression in the roots than in the leaves in greenhouse trials suggesting a possible explanation for poor tolerance to Fusarium root rot. Field trials are necessary to verify the agronomic performance and ecological relevance of the promising effects detected under laboratory conditions.

Genotype-independent and enhanced in planta Agrobacterium tumefaciens-mediated genetic transformation of peanut [Arachis hypogaea (L.)]

Agrobacterium infection and regeneration of the putatively transformed plant from the explant remains arduous for some crop species like peanut. Henceforth, a competent and reproducible in planta genetic transformation protocol is established for peanut cv. CO7 by standardizing various factors such as pre-culture duration, acetosyringone concentration, duration of co-cultivation, sonication and vacuum infiltration. In the present investigation, Agrobacterium tumefaciens strain EHA105 harboring the binary vector pCAMBIA1301-bar was used for transformation. The two-stage selection was carried out using 4 and 250 mg l^-1 BASTA^® to completely eliminate the chimeric and non-transformed plants. The transgene integration into plant genome was evaluated by GUS histochemical assay, polymerase chain reaction (PCR), and Southern blot hybridization. Among the various combinations and concentrations analyzed, highest transformation efficiency was obtained when the 2-day pre-cultured explants were subjected to sonication for 6 min and vacuum infiltrated for 3 min in Agrobacterium suspension, and co-cultivated on MS medium supplemented with 150 µM acetosyringone for 3 days. The fidelity of the standardized in planta transformation method was assessed in five peanut cultivars and all the cultivars responded positively with a transformation efficiency ranging from minimum 31.3% (with cv. CO6) to maximum 38.6% (with cv. TMV7). The in planta transformation method optimized in this study could be beneficial to develop superior peanut cultivars with desirable genetic traits.

Antifungal activity of chitinase II against Colletotrichum falcatum Went. causing red rot disease in transgenic sugarcane

We evaluated transgenic lines of sugarcane modified with the barley chitinase class-II gene to create resistance against the red rot causative agent Colletotrichum falcatum Went. Local sugarcane cultivar SP93 was transformed with a 690-bp coding sequence of the chitinase-II gene under the influence of a polyubiquitin promoter. Transgenic sugarcane lines (T 0) overexpressing the chitinase gene were obtained through a particle bombardment method with 13.3% transformation efficiency. Four transgenic sugarcane lines, SCT-03, SCT-05, SCT-15, and SCT-20, were tested for resistance against red rot by in vitro antifungal assays. Crude protein extracts from transgenic sugarcane plants SCT-03, SCT-05, SCT-15, and SCT-20 inhibited the mycelial growth of C. falcatum by 49%, 40%, 56%, and 52%, respectively, in a quantitative in vitro assay. Our findings revealed that two transgenic lines, SCT-15 and SCT-20, exhibited the highest endochitinase activity of 0.72 and 0.58 U/mL, respectively. Furthermore, transgenic lines SCT-15 and SCT-20 exhibited strong resistance against inoculated C. falcatum in an in vitro bioassay, as they remained healthy and green in comparison with the control sugarcane plants, which turned yellow and eventually died 3 weeks after infection. The mRNA expression of the transgene in the C. falcatum-inoculated transgenic sugarcane lines increased gradually compared to the control plant. The mRNA expression was the highest at 72 h in both transgenic lines and remained almost stable in the subsequent hours.

Genetic Engineering: A Possible Strategy for Protein-Energy Malnutrition Regulation

Protein-energy malnutrition (PEM) has adversely affected the generations of developing countries. It is a syndrome that in severity causes death. PEM generally affects infants of 1-5 age group. This manifestation is maintained till adulthood in the form of poor brain and body development. The developing nations are continuously making an effort to curb PEM. However, it is still a prime concern as it was in its early years of occurrence. Transgenic crops with high protein and enhanced nutrient content have been successfully developed. Present article reviews the studies documenting genetic engineering-mediated improvement in the pulses, cereals, legumes, fruits and other crop plants in terms of nutritional value, stress tolerance, longevity and productivity. Such genetically engineered crops can be used as a possible remedial tool to eradicate PEM.

Developing transgenic wheat to encounter rusts and powdery mildew by overexpressing barley chi26 gene for fungal resistance

BACKGROUND

The main aim of this study was to improve fungal resistance in bread wheat via transgenesis. Transgenic wheat plants harboring barley chitinase (chi26) gene, driven by maize ubi promoter, were obtained using biolistic bombardment, whereas the herbicide resistance gene, bar, driven by the CaMV 35S promoter was used as a selectable marker.

RESULTS

Molecular analysis confirmed the integration, copy number, and the level of expression of the chi26 gene in four independent transgenic events. Chitinase enzyme activity was detected using a standard enzymatic assay. The expression levels of chi26 gene in the different transgenic lines, compared to their respective controls, were determined using qRT-PCR. The transgene was silenced in some transgenic families across generations. Gene silencing in the present study seemed to be random and irreversible. The homozygous transgenic plants of T4, T5, T6, T8, and T9 generations were tested in the field for five growing seasons to evaluate their resistance against rusts and powdery mildew. The results indicated high chitinase activity at T0 and high transgene expression levels in few transgenic families. This resulted in high resistance against wheat rusts and powdery mildew under field conditions. It was indicated by proximate and chemical analyses that one of the transgenic families and the non-transgenic line were substantially equivalent.

CONCLUSION

Transgenic wheat with barley chi26 was found to be resistant even after five generations under artificial fungal infection conditions. One transgenic line was proved to be substantially equivalent as compared to the non-transgenic control.

Enhanced chitinase production by Chitinolyticbacter meiyuanensis SYBC-H1 using staged pH control

The pH of a microbiological culture is important for both cell growth and chitinase accumulation, but the optimal pH is not normally the same for both. The objective of this study was to investigate the effect of pH on chitinase production by Chitinolyticbacter meiyuanensis strain SYBC-H1 (ATCC BAA-2140) in a mineral medium. The results of batch culture at different pH values showed that the optimum pH for cell growth and chitinase production varied with time, although KOH produced the best results for cell growth and chitinase production, NaOH was chosen because of cost considerations. We designed a three-stage pH control strategy using NaOH as the neutralizing agent. Maximum cell growth (1.07 g dry cell weight/l) and maximum chitinase activity (13.6 U/ml) were observed after culture at 26°C for 72 h in a mineral medium. These values were greater by 129% and 162%, respectively, and the length of time to attain maximum chitinase activity was decreased by 12 h, compared with results from an earlier study (Hao et al., 2011b).

Co-expression of chimeric chitinase and a polygalacturonase-inhibiting protein in transgenic canola (Brassica napus) confers enhanced resistance to Sclerotinia sclerotiorum

OBJECTIVES

Sclerotinia stem rot (SSR) caused by Sclerotinia sclerotiorum is one of the major fungal diseases of canola. To develop resistance against this fungal disease, the chit42 from Trichoderma atroviride with chitin-binding domain and polygalacturonase-inhibiting protein 2 (PG1P2) of Phaseolus vulgaris were co-expressed in canola via Agrobacterium-mediated transformation.

RESULTS

Stable integration and expression of transgenes in T0 and T2 plants was confirmed by PCR, Southern blot and RT-PCR analyses. Chitinase activity and PGIP2 inhibition were detected by colorimetric and agarose diffusion assay in transgenic lines but not in untransformed plants. The crude proteins from single copy transformant leaves having high chitinase and PGIP2 activity (T16, T8 and T3), showed up to 44 % inhibition of S. sclerotiorum hyphal growth. The homozygous T2 plants, showing inheritance in Mendelian fashion (3:1), were further evaluated under greenhouse conditions for resistance to S. sclerotiorum. Intact plants contaminated with mycelia showed resistance through delayed onset of the disease and restricted size and expansion of lesions as compared to wild type plants.

CONCLUSIONS

Combined expression of chimeric chit42 and pgip2 in Brassica napus L. provide subsequent protection against SSR disease and can be helpful in increasing the canola production in Iran.

Synergistic Action of a Metalloprotease and a Serine Protease from Fusarium oxysporum f. sp. lycopersici Cleaves Chitin-Binding Tomato Chitinases, Reduces Their Antifungal Activity, and Enhances Fungal Virulence

As part of their defense strategy against fungal pathogens, plants secrete chitinases that degrade chitin, the major structural component of fungal cell walls. Some fungi are not sensitive to plant chitinases because they secrete chitin-binding effector proteins that protect their cell wall against these enzymes. However, it is not known how fungal pathogens that lack chitin-binding effectors overcome this plant defense barrier. Here, we investigated the ability of fungal tomato pathogens to cleave chitin-binding domain (CBD)-containing chitinases and its effect on fungal virulence. Four tomato CBD chitinases were produced in Pichia pastoris and were incubated with secreted proteins isolated from seven fungal tomato pathogens. Of these, Fusarium oxysporum f. sp. lycopersici, Verticillium dahliae, and Botrytis cinerea were able to cleave the extracellular tomato chitinases SlChi1 and SlChi13. Cleavage by F. oxysporum removed the CBD from the N-terminus, shown by mass spectrometry, and significantly reduced the chitinase and antifungal activity of both chitinases. Both secreted metalloprotease FoMep1 and serine protease FoSep1 were responsible for this cleavage. Double deletion mutants of FoMep1 and FoSep1 of F. oxysporum lacked chitinase cleavage activity on SlChi1 and SlChi13 and showed reduced virulence on tomato. These results demonstrate the importance of plant chitinase cleavage in fungal virulence.

Progress in genetic engineering of peanut (Arachis hypogaea L.)--a review

Peanut (Arachis hypogaea L.) is a major species of the family, Leguminosae, and economically important not only for vegetable oil but as a source of proteins, minerals and vitamins. It is widely grown in the semi-arid tropics and plays a role in the world agricultural economy. Peanut production and productivity is constrained by several biotic (insect pests and diseases) and abiotic (drought, salinity, water logging and temperature aberrations) stresses, as a result of which crop experiences serious economic losses. Genetic engineering techniques such as Agrobacterium tumefaciens and DNA-bombardment-mediated transformation are used as powerful tools to complement conventional breeding and expedite peanut improvement by the introduction of agronomically useful traits in high-yield background. Resistance to several fungal, virus and insect pest have been achieved through variety of approaches ranging from gene coding for cell wall component, pathogenesis-related proteins, oxalate oxidase, bacterial chloroperoxidase, coat proteins, RNA interference, crystal proteins etc. To develop transgenic plants withstanding major abiotic stresses, genes coding transcription factors for drought and salinity, cytokinin biosynthesis, nucleic acid processing, ion antiporter and human antiapoptotic have been used. Moreover, peanut has also been used in vaccine production for the control of several animal diseases. In addition to above, this study also presents a comprehensive account on the influence of some important factors on peanut genetic engineering. Future research thrusts not only suggest the use of different approaches for higher expression of transgene(s) but also provide a way forward for the improvement of crops.

The battle in the apoplast: further insights into the roles of proteases and their inhibitors in plant-pathogen interactions

Upon host penetration, fungal pathogens secrete a plethora of effectors to promote disease, including proteases that degrade plant antimicrobial proteins, and protease inhibitors (PIs) that inhibit plant proteases with antimicrobial activity. Conversely, plants secrete proteases and PIs to protect themselves against pathogens or to mediate recognition of pathogen proteases and PIs, which leads to induction of defense responses. Many examples of proteases and PIs mediating effector-triggered immunity in host plants have been reported in the literature, but little is known about their role in compromising basal defense responses induced by microbe-associated molecular patterns. Recently, several reports appeared in literature on secreted fungal proteases that modify or degrade pathogenesis-related proteins, including plant chitinases or PIs that compromise their activities. This prompted us to review the recent advances on proteases and PIs involved in fungal virulence and plant defense. Proteases and PIs from plants and their fungal pathogens play an important role in the arms race between plants and pathogens, which has resulted in co-evolutionary diversification and adaptation shaping pathogen lifestyles.

Transcriptome Analysis of Early Responsive Genes in Rice during Magnaporthe oryzae Infection

Rice blast disease caused by Magnaporthe oryzae is one of the most serious diseases of cultivated rice (Oryza sativa L.) in most rice-growing regions of the world. In order to investigate early response genes in rice, we utilized the transcriptome analysis approach using a 300 K tilling microarray to rice leaves infected with compatible and incompatible M. oryzae strains. Prior to the microarray experiment, total RNA was validated by measuring the differential expression of rice defense-related marker genes (chitinase 2, barwin, PBZ1, and PR-10) by RT-PCR, and phytoalexins (sakuranetin and momilactone A) with HPLC. Microarray analysis revealed that 231 genes were up-regulated (>2 fold change, p < 0.05) in the incompatible interaction compared to the compatible one. Highly expressed genes were functionally characterized into metabolic processes and oxidation-reduction categories. The oxidative stress response was induced in both early and later infection stages. Biotic stress overview from MapMan analysis revealed that the phytohormone ethylene as well as signaling molecules jasmonic acid and salicylic acid is important for defense gene regulation. WRKY and Myb transcription factors were also involved in signal transduction processes. Additionally, receptor-like kinases were more likely associated with the defense response, and their expression patterns were validated by RT-PCR. Our results suggest that candidate genes, including receptor-like protein kinases, may play a key role in disease resistance against M. oryzae attack.

An efficient method of agrobacterium-mediated genetic transformation and regeneration in local Indian cultivar of groundnut (Arachis hypogaea) using grafting

Groundnut (Arachis hypogaea L.) is an industrial crop used as a source of edible oil and nutrients. In this study, an efficient method of regeneration and Agrobacterium-mediated genetic transformation is reported for a local cultivar GG-20 using de-embryonated cotyledon explant. A high regeneration 52.69 ± 2.32 % was achieved by this method with 66.6 μM 6-benzylaminopurine (BAP), while the highest number of shoot buds per explant, 17.67 ± 3.51, was found with 20 μM BAP and 10 μM 2,4-dichlorophenoxyacetic acid (2,4-D). The bacterial culture OD, acetosyringone and L-cysteine concentration were optimized as 1.8, 200 μM and 50 mg L(-1), respectively, in co-cultivation media. It was observed that the addition of 2,4-D in co-cultivation media induced accumulation of endogenous indole-3-acetic acid (IAA). The optimized protocol exhibited 85 % transformation efficiency followed by 14.65 ± 1.06 % regeneration, of which 3.82 ± 0.6 % explants were survived on hygromycin after selection. Finally, 14.58 ± 2.95 % shoots (regenerated on survived explants) were rooted on rooting media (RM3). In grafting method, regenerated shoots (after hygromycin selection) were grafted on the non-transformed stocks with 100 % survival and new leaves emerged in 3 weeks. The putative transgenic plants were then confirmed by PCR, Southern hybridization, reverse transcriptase PCR (RT-PCR) and β-glucuronidase (GUS) histochemical assay. The reported method is efficient and rapid and can also be applied to other crops which are recalcitrant and difficult in rooting.

Oligonucleotide treatment causes flax β-glucanase up-regulation via changes in gene-body methylation

BACKGROUND

Nowadays, the challenge for biotechnology is to develop tools for agriculture and industry to provide plants characterized by productivity and quality that will satisfy the growing demand for different kinds of natural products. To meet the challenge, the generation and application of genetically modified plants is justified. However, the strong social resistance to genetically modified organisms and restrictive regulations in European Union countries necessitated the development of a new technology for new plant types generation which uses the knowledge resulting from analysis of genetically modified plants to generate favourably altered plants while omitting the introduction of heterologous genes to their genome. Four-year experiments led to the development of a technology inducing heritable epigenetic gene activation without transgenesis.

RESULTS

The method comprises the induction of changes in methylation/demethylation of the endogenous gene by the plant's treatment with short oligodeoxynucleotides antisense to the coding region. In vitro cultured plants and F3 generation flax plants overproducing the β-1,3-glucanase gene (EMO-βGlu flax) were characterized by up-regulation of β-glucanase and chitinase genes, decreases in the methylation of CCGG sequences in the β-glucanase gene and in total DNA methylation and, more importantly, reasonable resistance against Fusarium infection. In addition, EMO-βGlu flax obtained by this technology showed similar features as those obtained by genetic engineering.

CONCLUSION

To our best knowledge, this is the first report on plant gene activation by treatment with oligodeoxynucleotides homologous to the coding region of the gene. Apart from the evident effectiveness, the most important issue is that the EMO method allows generation of favourably altered plants, whose cultivation makes the plant producer independent from the complicated procedure of obtaining an agreement on GMO release into the environment and whose products might be more easily introduced to the global market.

Overview of plant chitinases identified as food allergens

Food allergies are induced by proteins belonging to a limited number of families. Unfortunately, relationships between protein structure and capacity to induce the immune response have not been completely clarified yet, which precludes possible improvements in the diagnosis, prevention, and therapy of allergies. Plant chitinases constitute a good example of food allergenic proteins for which structural analysis of allergenicity has only been carried out partially. In plants, there are at least five structural classes of chitinases plus a number of chitinase-related polypeptides. Their allergenicity has been mostly investigated for chitinases of class I, due to both their higher prevalence among plant chitinases and by the high structural similarity between their substrate-binding domain and hevein, a well-known allergen present in the latex of rubber trees. Even if allergenic molecules have been identified for at least three other classes of plant chitinases, the involvement of the different structural motifs in the allergenicity of molecules has been disregarded so far. In this review, we provide a structurally based catalog of plant chitinases investigated for allergenicity, which could be a useful base for further studies aimed at better clarifying the structure-allergenicity relationships for this protein family.

Ectopic over-expression of peroxisomal ascorbate peroxidase (SbpAPX) gene confers salt stress tolerance in transgenic peanut (Arachis hypogaea)

Peroxisomal ascorbate peroxidase gene (SbpAPX) of an extreme halophyte Salicornia brachiata imparts abiotic stress endurance and plays a key role in the protection against oxidative stress. The cloned SbpAPX gene was transformed to local variety of peanut and about 100 transgenic plants were developed using optimized in vitro regeneration and Agrobacterium mediated genetic transformation method. The T0 transgenic plants were confirmed for the gene integration; grown under controlled condition in containment green house facility; seeds were harvested and T1 plants were raised. Transgenic plants (T1) were further confirmed by PCR using gene specific primers and histochemical GUS assay. About 40 transgenic plants (T1) were selected randomly and subjected for salt stress tolerance study. Transgenic plants remained green however non-transgenic plants showed bleaching and yellowish leaves under salt stress conditions. Under stress condition, transgenic plants continued normal growth and completed their life cycle. Transgenic peanut plants exhibited adequate tolerance under salt stress condition and thus could be explored for the cultivation in salt affected areas for the sustainable agriculture.

Caterpillar attack triggers accumulation of the toxic maize protein RIP2

Some plant-derived anti-herbivore defensive proteins are induced by insect feeding, resist digestion in the caterpillar gut and are eliminated in the frass. We have identified several maize proteins in fall armyworm (Spodoptera frugiperda) frass that potentially play a role in herbivore defense. Furthermore, the toxicity of one of these proteins, ribosome-inactivating protein 2 (RIP2), was assessed and factors regulating its accumulation were determined. To understand factors regulating RIP2 protein accumulation, maize (Zea mays) plants were infested with fall armyworm larvae or treated with exogenous hormones. The toxicity of recombinant RIP2 protein against fall armyworm was tested. The results show that RIP2 protein is synthesized as an inactive proenzyme that can be processed in the caterpillar gut. Also, caterpillar feeding, but not mechanical wounding, induced foliar RIP2 protein accumulation. Quantitative real-time PCR indicated that RIP2 transcripts were rapidly induced (1 h) and immunoblot analysis indicated that RIP2 protein accumulated soon after attack and was present in the leaf for up to 4 d after caterpillar removal. Several phytohormones, including methyl jasmonate, ethylene, and abscisic acid, regulated RIP2 protein expression. Furthermore, bioassays of purified recombinant RIP2 protein against fall armyworm significantly retarded caterpillar growth. We conclude that the toxic protein RIP2 is induced by caterpillar feeding and is one of a potential suite of proteins that defend maize against chewing herbivores.

Proteomic investigation of response to FORL infection in tomato roots

Fusarium oxysporum f. sp. radicis-lycopersici (FORL) leading to fusarium crown and root rot is considered one of the most destructive tomato soilborne diseases occurring in greenhouse and field crops. In this study, response to FORL infection in tomato roots was investigated by differential proteomics in susceptible (Monalbo) and resistant (Momor) isogenic tomato lines, thus leading to identify 33 proteins whose amount changed depending on the pathogen infection, and/or on the two genotypes. FORL infection induced accumulation of pathogen-related proteins (PR proteins) displaying glucanase and endochitinases activity or involved in redox processes in the Monalbo genotype. Interestingly, the level of the above mentioned PR proteins was not influenced by FORL infection in the resistant tomato line, while other proteins involved in general response mechanisms to biotic and/or abiotic stresses showed significant quantitative differences. In particular, the increased level of proteins participating to arginine metabolism and glutathione S-transferase (GST; EC 2.5.1.18) as well as that of protein LOC544002 and phosphoprotein ECPP44-like, suggested their key role in pathogen defence.

Transgenic expression of plant chitinases to enhance disease resistance

Crop plants have evolved an array of mechanisms to counter biotic and abiotic stresses. Many pathogenesis-related proteins are expressed by plants during the attack of pathogens. Advances in recombinant DNA technology and understanding of plant-microbe interactions at the molecular level have paved the way for isolation and characterization of genes encoding such proteins, including chitinases. Chitinases are included in families 18 and 19 of glycosyl hydrolases (according to www.cazy.org ) and they are further categorized into seven major classes based on their aminoacid sequence homology, three-dimensional structures, and hydrolytic mechanisms of catalytic reactions. Although chitin is not a component of plant cell walls, plant chitinases are involved in development and non-specific stress responses. Also, chitinase genes sourced from plants have been successfully over-expressed in crop plants to combat fungal pathogens. Crops such as tomato, potato, maize, groundnut, mustard, finger millet, cotton, lychee, banana, grape, wheat and rice have been successfully engineered for fungal resistance either with chitinase alone or in combination with other PR proteins.

Enhanced resistance to stripe rust disease in transgenic wheat expressing the rice chitinase gene RC24

Stripe rust is a devastating fungal disease of wheat worldwide which is primarily caused by Puccinia striiformis f. sp tritici. Transgenic wheat (Triticum aestivum L.) expressing rice class chitinase gene RC24 were developed by particle bombardment of immature embryos and tested for resistance to Puccinia striiformis f.sp tritici. under greenhouse and field conditions. Putative transformants were selected on kanamycin-containing media. Polymease chain reaction indicated that RC24 was transferred into 17 transformants obtained from bombardment of 1,684 immature embryos. Integration of RC24 was confirmed by Southern blot with a RC24-labeled probe and expression of RC24 was verified by RT-PCR. Nine transgenic T1 lines exhibited enhanced resistance to stripe rust infection with lines XN8 and BF4 showing the highest level of resistance. Southern blot hybridization confirmed the stable inheritance of RC24 in transgenic T1 plants. Resistance to stripe rust in transgenic T2 and T3 XN8 and BF4 plants was confirmed over two consecutive years in the field. Increased yield (27-36 %) was recorded for transgenic T2 and T3 XN8 and BF4 plants compared to controls. These results suggest that rice class I chitinase RC24 can be used to engineer stripe rust resistance in wheat.

Fibres from flax overproducing β-1,3-glucanase show increased accumulation of pectin and phenolics and thus higher antioxidant capacity

BACKGROUND

Recently, in order to improve the resistance of flax plants to pathogen infection, transgenic flax that overproduces β-1,3-glucanase was created. β-1,3-glucanase is a PR protein that hydrolyses the β-glucans, which are a major component of the cell wall in many groups of fungi. For this study, we used fourth-generation field-cultivated plants of the Fusarium -resistant transgenic line B14 to evaluate how overexpression of the β-1,3-glucanase gene influences the quantity, quality and composition of flax fibres, which are the main product obtained from flax straw.

RESULTS

Overproduction of β-1,3-glucanase did not affect the quantity of the fibre obtained from the flax straw and did not significantly alter the essential mechanical characteristics of the retted fibres. However, changes in the contents of the major components of the cell wall (cellulose, hemicellulose, pectin and lignin) were revealed. Overexpression of the β-1,3-glucanase gene resulted in higher cellulose, hemicellulose and pectin contents and a lower lignin content in the fibres. Increases in the uronic acid content in particular fractions (with the exception of the 1 M KOH-soluble fraction of hemicelluloses) and changes in the sugar composition of the cell wall were detected in the fibres of the transgenic flax when compared to the contents for the control plants. The callose content was lower in the fibres of the transgenic flax. Additionally, the analysis of phenolic compound contents in five fractions of the cell wall revealed important changes, which were reflected in the antioxidant potential of these fractions.

CONCLUSION

Overexpression of the β-1,3-glucanase gene has a significant influence on the biochemical composition of flax fibres. The constitutive overproduction of β-1,3-glucanase causes a decrease in the callose content, and the resulting excess glucose serves as a substrate for the production of other polysaccharides. The monosaccharide excess redirects the phenolic compounds to bind with polysaccharides instead of to partake in lignin synthesis. The mechanical properties of the transgenic fibres are strengthened by their improved biochemical composition, and the increased antioxidant potential of the fibres supports the potential use of transgenic flax fibres for biomedical applications.