Agrobacterium tumefaciens-mediated transformation of taro (Colocasia esculenta (L.) Schott) with a rice chitinase gene for improved tolerance to a fungal pathogen Sclerotium rolfsii

Genetic engineering and genome editing technologies as catalyst for Africa's food security: the case of plant biotechnology in Nigeria

Many African countries are unable to meet the food demands of their growing population and the situation is worsened by climate change and disease outbreaks. This issue of food insecurity may lead to a crisis of epic proportion if effective measures are not in place to make more food available. Thus, deploying biotechnology towards the improvement of existing crop varieties for tolerance or resistance to both biotic and abiotic stresses is crucial to increasing crop production. In order to optimize crop production, several African countries have implemented strategies to make the most of this innovative technology. For example, Nigerian government has implemented the National Biotechnology Policy to facilitate capacity building, research, bioresource development and commercialization of biotechnology products for over two decades. Several government ministries, research centers, universities, and agencies have worked together to implement the policy, resulting in the release of some genetically modified crops to farmers for cultivation and Commercialization, which is a significant accomplishment. However, the transgenic crops were only brought to Nigeria for confined field trials; the manufacturing of the transgenic crops took place outside the country. This may have contributed to the suspicion of pressure groups and embolden proponents of biotechnology as an alien technology. Likewise, this may also be the underlying issue preventing the adoption of biotechnology products in other African countries. It is therefore necessary that African universities develop capacity in various aspects of biotechnology, to continuously train indigenous scientists who can generate innovative ideas tailored towards solving problems that are peculiar to respective country. Therefore, this study intends to establish the role of genetic engineering and genome editing towards the achievement of food security in Africa while using Nigeria as a case study. In our opinion, biotechnology approaches will not only complement conventional breeding methods in the pursuit of crop improvements, but it remains a viable and sustainable means of tackling specific issues hindering optimal crop production. Furthermore, we suggest that financial institutions should offer low-interest loans to new businesses. In order to promote the growth of biotechnology products, especially through the creation of jobs and revenues through molecular farming.

Pathogenesis-related proteins and peptides as promising tools for engineering plants with multiple stress tolerance

Pathogenesis-related (PR) proteins and antimicrobial peptides (AMPs) are a group of diverse molecules that are induced by phytopathogens as well as defense related signaling molecules. They are the key components of plant innate immune system especially systemic acquired resistance (SAR), and are widely used as diagnostic molecular markers of defense signaling pathways. Although, PR proteins and peptides have been isolated much before but their biological function remains largely enigmatic despite the availability of new scientific tools. The earlier studies have demonstrated that PR genes provide enhanced resistance against both biotic and abiotic stresses, which make them one of the most promising candidates for developing multiple stress tolerant crop varieties. In this regard, plant genetic engineering technology is widely accepted as one of the most fascinating approach to develop the disease resistant transgenic crops using different antimicrobial genes like PR genes. Overexpression of PR genes (chitinase, glucanase, thaumatin, defensin and thionin) individually or in combination have greatly uplifted the level of defense response in plants against a wide range of pathogens. However, the detailed knowledge of signaling pathways that regulates the expression of these versatile proteins is critical for improving crop plants to multiple stresses, which is the future theme of plant stress biology. Hence, this review provides an overall overview on the PR proteins like their classification, role in multiple stresses (biotic and abiotic) as well as in various plant defense signaling cascades. We also highlight the success and snags of transgenic plants expressing PR proteins and peptides.

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.

Characterization of two PEBP genes, SrFT and SrMFT, in thermogenic skunk cabbage (Symplocarpus renifolius)

Floral thermogenesis has been found in dozens of primitive seed plants and the reproductive organs in these plants produce heat during anthesis. Thus, characterization of the molecular mechanisms underlying flowering is required to fully understand the role of thermogenesis, but this aspect of thermogenic plant development is largely unknown. In this study, extensive database searches and cloning experiments suggest that thermogenic skunk cabbage (Symplocarpus renifolius), which is a member of the family Araceae, possesses two genes encoding phosphatidyl ethanolamine-binding proteins (PEBP), FLOWERING LOCUS T (SrFT) and MOTHER OF FT AND TFL1 (SrMFT). Functional analyses of SrFT and SrMFT in Arabidopsis indicate that SrFT promotes flowering, whereas SrMFT does not. In S. renifolius, the stage- and tissue-specific expression of SrFT was more evident than that of SrMFT. SrFT was highly expressed in flowers and leaves and was mainly localized in fibrovascular tissues. In addition, microarray analysis revealed that, within floral tissues, SrFT was co-regulated with the genes associated with cellular respiration and mitochondrial function, including ALTERNATIVE OXIDASE gene proposed to play a major role in floral thermogenesis. Taken together, these data suggest that, among the PEBP genes, SrFT plays a role in flowering and floral development in the thermogenic skunk cabbage.

Expression of Rice Chitinase Gene in Genetically Engineered Tomato Confers Enhanced Resistance to Fusarium Wilt and Early Blight

This is the first study reporting the evaluation of transgenic lines of tomato harboring rice chitinase (RCG3) gene for resistance to two important fungal pathogens Fusarium oxysporum f. sp. lycopersici (Fol) causing fusarium wilt and Alternaria solani causing early blight (EB). In this study, three transgenic lines TL1, TL2 and TL3 of tomato Solanum lycopersicum Mill. cv. Riogrande genetically engineered with rice chitinase (RCG 3) gene and their R1 progeny was tested for resistance to Fol by root dip method and A. solani by detached leaf assay. All the R0 transgenic lines were highly resistant to these fungal pathogens compared to non-transgenic control plants. The pattern of segregation of three independent transformant for Fol and A. solani was also studied. Mendelian segregation was observed in transgenic lines 2 and 3 while it was not observed in transgenic line 1. It was concluded that introduction of chitinase gene in susceptible cultivar of tomato not only enhanced the resistance but was stably inherited in transgenic lines 2 and 3.

Taro (Colocasia esculenta (L.) Schott)

Genetic engineering of taro is an effective method to improve taro quality and the resistance to various diseases of taro. Agrobacterium tumefaciens-mediated transformation of taro is more efficient than the particle bombardment transformation method based on current research. The development of a regeneration system starting from taro shoot tip explants could produce dasheen mosaic virus (DsMV)-free plantlets. Highly regenerative calluses could be developed from DsMV-free, in vitro plantlets on the Murashige and Skoog (MS) medium with 2 mg/L BA and 1 mg/L NAA (M5 medium). The Agrobacterium tumefaciens-mediated transformation method is reported in this chapter. The highly regenerative calluses were selected and cocultivated with the Agrobacterium strain EHA105 harboring the binary vector PBI121 with either a rice chitinase gene chi11 or a wheat oxalate oxidase gene gf2.8. After cocultivation for 3-4 days, these calluses were transferred to selection medium (M5 medium) containing 50 mg/L Geneticin G418 and grown for 3 months in the dark. Transgenic shoot lines could be induced and selected on the MS medium containing 4 mg/L BA (M15 medium) and 50 mg/L Geneticin G418 for 3 months further in the light. Molecular analyses are used to confirm the stable transformation and expression of the disease resistance gene chi11 or gf2.8. Pathologic bioassays could be used to demonstrate whether the transgenic plants had increased disease resistance to taro pathogens Sclerotium rolfsii or Phytophthora colocasiae.

Chitinase genes LbCHI31 and LbCHI32 from Limonium bicolor were successfully expressed in Escherichia coli and exhibit recombinant chitinase activities

The two chitinase genes, LbCHI31 and LbCHI32 from Limonium bicolor, were, respectively, expressed in Escherichia coli BL21 strain. The intracellular recombinant chitinases, inrCHI31 and inrCHI32, and the extracellular exrCHI31 and exrCHI32 could be produced into E. coli. The exrCHI31 and exrCHI32 can be secreted into extracellular medium. The optimal reaction condition for inrCHI31 was 5 mmol/L of Mn²⁺ at 40°C and pH 5.0 with an activity of 0.772 U using Alternaria alternata cell wall as substrate. The optimal condition of inrCHI32 was 5 mmol/L of Ba²⁺ at 45°C and pH 5.0 with an activity of 0.792 U using Valsa sordida cell wall as substrate. The optimal reaction condition of exrCHI31 was 5 mmol/L of Zn²⁺ at 40°C and pH 5.0, and the activity was 0.921 U using the A. alternata cell wall as substrate. Simultaneously, the optimal condition of exrCHI32 was 5 mmol/L of K⁺ at 45°C and pH 5.0, with V. sordida cell wall as the substrate, and the activity was 0.897 U. Furthermore, the activities of extracellular recombinant enzymes on fungal cell walls and compounds were generally higher than those of the intracellular recombinant enzymes. Recombinant exrCHI31 and exrCHI32 have better hydrolytic ability on cell walls of different fungi than synthetic chitins and obviously showed activity against A. alternata.

Biochemical characterization of chitinase 2 expressed during the autolytic phase of the inky cap, Coprinellus congregatus

Fungal cell walls consist of various glucans and chitin. The inky cap, Coprinellus congregatus, produces mushrooms at 25°C in a regime of 15 h light/9 h dark, and then the mushroom is autolyzed rapidly to generate black liquid droplets in which no cell walls are detected by microscopy. Chitinase cDNA from the mature mushroom tissues of C. congregatus, which consisted of 1,622 nucleotides (chi2), was successfully cloned using the rapid amplification of cDNA ends polymerase chain reaction technique. The deduced 498 amino acid sequence of Chi2 had a conserved catalytic domain as in other fungal chitinase family 18 enzymes. The Chi2 enzyme was purified from the Pichia pastoris expression system, and its estimated molecular weight was 68 kDa. The optimum pH and temperature of Chi2 was pH 4.0 and 35°C, respectively when 4-nitrophenyl N,N'-diacetyl-β-D-chitobioside was used as the substrate. The K m value and V max for the substrate A, 4-nitrophenyl N,N'-diacetyl-β-D-chitobioside, was 0.175 mM and 0.16 OD min(-1)unit(-1), respectively.

Genetic engineering of crop plants for fungal resistance: role of antifungal genes

Fungal diseases damage crop plants and affect agricultural production. Transgenic plants have been produced by inserting antifungal genes to confer resistance against fungal pathogens. Genes of fungal cell wall-degrading enzymes, such as chitinase and glucanase, are frequently used to produce fungal-resistant transgenic crop plants. In this review, we summarize the details of various transformation studies to develop fungal resistance in crop plants.

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.

Enhanced expression of chitinase during the autolysis of mushroom in Coprinellus congregatus

Fungal cell walls consist of various glucans and chitin. An inky cap, Coprinellus congregates, produced mushrooms at 25 degrees C in a regime of 15 h light/9 h dark, and then the mushroom was autolyzed rapidly to generate black liquid droplets where no cell wall was detected by microscopy. A chitinase cDNA from the matured mushroom cells of C. congregates that consisted of 1,541 nucleotides was successfully cloned using the rapid amplification of cDNA ends (RACE)-PCR technique. Its deduced 441 amino acid sequence had the conserved catalytic domain as in other fungal chitinase family 18. Chitinase activity was higher at the matured mushroom stage than primordial and young mushroom stage. When the expression of the cloned chitinase was examined by real-time PCR using the chitinase-specific primers, it was increased more than twice to 20 times during the autolytic process of mushroom than young mushroom or primordial stages, respectively.

Molecular cloning and characterization of the promoter for the multiple stress-inducible gene BjCHI1 from Brassica juncea

We have previously isolated a Brassica juncea cDNA encoding a novel chitinase BjCHI1 with two chitin-binding domains (Zhao and Chye in Plant Mol Biol 40:1009-1018, 1999). The expression of BjCHI1 was highly inducible by methyl jasmonate (MeJA) treatment, wounding, caterpillar feeding, and pathogenic fungal infection. These observations suggest that the promoter of BjCHI1 gene might contain specific cis-acting elements for stress responses. Here, we report the cloning and characterization of the BjCHI1 promoter. A 1,098 bp BjCHI1 genomic DNA fragment upstream of the ATG start codon was isolated by PCR walking and various constructs were made by fusing the BjCHI1 promoter or its derivatives to beta-glucuronidase reporter gene. The transgenic Arabidopsis plants showed that the BjCHI1 promoter responded to wounding and MeJA treatment, and to treatments with either NaCl or polyethyleneglycol (PEG 6000), indicating that the BjCHI1 promoter responses to both biotic and abiotic stresses. A transient gene expression system of Nicotiana benthamiana leaves was adopted for promoter deletion analysis, and the results showed that a 76 bp region from -695 to -620 in the BjCHI1 promoter was necessary for MeJA-responsive expression. Furthermore, removal of a conserved T/G-box (AACGTG) at -353 to -348 of the promoter greatly reduced the induction by MeJA. This is the first T/G-box element identified in a chitinase gene promoter. Gain-of-function analysis demonstrated that the cis-acting element present in the 76 bp region requires coupling with the T/G-box to confer full magnitude of BjCHI1 induction by MeJA.