Impact of Transgenic Brassica napus Harboring the Antifungal Synthetic Chitinase (NiC) Gene on Rhizosphere Microbial Diversity and Enzyme Activities

Abstract

Transgenic Brassica napus harboring the synthetic chitinase (NiC) gene exhibits broad-spectrum antifungal resistance. As the rhizosphere microorganisms play an important role in element cycling and nutrient transformation, therefore, biosafety assessment of NiC containing transgenic plants on soil ecosystem is a regulatory requirement. The current study is designed to evaluate the impact of NiC gene on the rhizosphere enzyme activities and microbial community structure. The transgenic lines with the synthetic chitinase gene (NiC) showed resistance to Alternaria brassicicola, a common disease causing fungal pathogen. The rhizosphere enzyme analysis showed no significant difference in the activities of fivesoil enzymes: alkalyine phosphomonoestarase, arylsulphatase, β-glucosidase, urease and sucrase between the transgenic and non-transgenic lines of B. napus varieties, Durr-e-NIFA (DN) and Abasyne-95 (AB-95). However, varietal differences were observed based on the analysis of molecular variance. Some individual enzymes were significantly different in the transgenic lines from those of non-transgenic but the results were not reproducible in the second trail and thus were considered as environmental effect. Genotypic diversity of soil microbes through 16S–23S rRNA intergenic spacer region amplification was conducted to evaluate the potential impact of the transgene. No significant diversity (4% for bacteria and 12% for fungal) between soil microbes of NiC B. napus and the non-transgenic lines was found. However, significant varietal differences were observed between DN and AB-95 with 79% for bacterial and 54% for fungal diversity. We conclude that the NiC B. napus lines may not affect the microbial enzyme activities and community structure of the rhizosphere soil. Varietal differences might be responsible for minor changes in the tested parameters.

Allelopathic assessment for the environmental biosafety of the transgenic oilseed rape lines harboring the antifungal synthetic chitinase (NiC) gene

“…Data for all these tests showed no significant differences in transgenic and non-transgenic lines of DN and AB-95 varieties. Although, slightly variable expression levels were recorded for transgenic lines of both varieties and these differences were somehow reflected in the antifungal assay as previously described (Khan et al, 2017). Previous reports on similar lines represent their inhibitory effect on causal fungi; however, no significant impact of these two lines was observed on the allelopathic parameters.…”

“…Antifungal assay of the transgenic and wild type control lines: In our previous study, we conducted the antifungal analysis on similar NiC-lines of DN and AB-95 varieties (Khan et al, 2017). Leaves extracted proteins of different lines were used to conducted the antifungal activity of against the mycellial growth of Alternaria brassicicola on potato dextrose agar (PDA) media.…”

“…Plant material and experimental design: Two varieties of B. napus (Durre-NIFA-DN) and Abaseen-95-AB-95) were genetically engineered with the antifungal synthetic chitinase (NiC) gene (Khan et al, 2013). The transgenic lines were further evaluated for antifungal activity (Khan et al, 2017). Three transgenic lines of Durre-NIFA (DN-13, DN-120, DN-127) and three transgenic lines of Abaseen-95 (AB-11, AB-18, AB-31) were used; whereas, the DN and AB-95 were used as the corresponding non-transgenic control plants.…”

Cultivation of Drought-Tolerant and Insect-Resistant Rice Affects Soil Bacterial, but Not Fungal, Abundances and Community Structures

“…Importantly, the potential environmental effects of newly developed cultivars must be evaluated through environmental risk assessment before the cultivation of transgenic plants for commercial purposes ( National Research Council, 2002 ). Environmental risk assessments are based on precautionary principles and they are practiced on a case-by-case basis by taking into consideration the nature of the plant, trait and the potential receiving environment ( Khan et al, 2017 ). One of the major potential environmental risks associated with the use of drought- and insect-resistant rice varieties is the effect on soil and the inhabiting non-target organisms, including bacteria and fungi.…”

“…Moreover, considering the Bt protein that is released in root exudates from transgenic Bt plants ( Saxena et al, 1999 ) and variation in drought stress-response gene expression, we hypothesized that drought- and insect-resistant rice varieties are likely to produce unintended effects on soil bacterial and the fungal communities. In addition, it is clear that factors, such as soil physical–chemical properties and plant genotypes, greatly influence the corresponding rhizosphere microbial community compositions ( Khan et al, 2017 ). The extent to which these factors, including soil Bt protein exposure, influence and contribute to indigenous microbial community is not yet fully understood.…”