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. 2018 Dec 25;35(4):393–397. doi: 10.5511/plantbiotechnology.18.0831a

Environmental risk assessment of impacts of transgenic Eucalyptus camaldulensis events highly expressing bacterial Choline Oxidase A gene

Ngoc-Ha Thi Tran 1, Taichi Oguchi 2,3,*, Etsuko Matsunaga 4, Akiyoshi Kawaoka 4, Kazuo N Watanabe 2,3, Akira Kikuchi 2,3
PMCID: PMC6905223  PMID: 31892828

Abstract

Under the Japanese biosafety regulatory framework for transgenic plants, data for assessing a transgenic plant’s impact on biodiversity must be submitted in order to obtain approval for a confined field trial. We recently reported the development of four novel transgenic Eucalyptus camaldulensis clones expressing the bacterial choline oxidase A (codA) gene, i.e., codAH-1, codAH-2, codAN-1, and codAN-2, and evaluated their abiotic tolerance by semiconfined screen house trial cultivation. Here we evaluated the impacts of the transgenic E. camaldulensis clones on productivities of harmful substances from those clones to affect soil microorganisms and/or other plants in the environment. A comparison of the assessment data between the transgenic trees and non-transgenic comparators showed no significant difference in potential impacts on biodiversity. The results contribute to sound-science evidence ensuring substantial equivalence between transgenic and non-transgenic E. camaldulensis.

Keywords: biosafety, choline oxidase A (codA), environmental risk assessment (ERA), Eucalyptus camaldulensis, transgenic trees

Biotech crops have been used in commercial cultivation for more than 20 years and in 2016 were planted in 26 countries; they have demonstrated their advantages, with less clear evidence of a risk to the environment (ISAAA 2016, 2017; National Academies of Sciences, Engineering, and Medicine 2016; Parisi et al. 2016). This is because biotech events need to meet not only rules established by various countries but also all regulatory demands set forth in the Cartagena Protocol on Biosafety to the Convention on Biological Diversity (CBD) before being approved for release in commercial areas. In the case of USA and Canada, the large producers of biotech crops, although they have not ratified Cartagena Protocol on Biosafety, they have their own serious regulation framework for releasing biotechnology plants to commercial areas (McHughen and Smyth 2012; National Academies of Sciences, Engineering, and Medicine 2017; Smyth and McHughen 2012). In general, most of the concern of these regulations focus on the impacts of a biotech plant on biodiversity, the balance of the ecology of the receiving environment, and whether there is any potential impact of a biotech plant on its environment. The evaluation protocols for transgenic plants differ from country to country and depend case by case on the biotech event. With more than two decades of experience in biotech crops, it seems that there is a clear frame for evaluating the environmental safety of transgenic crops. In the case of biotech application on plantation trees, the basic concept of environmental risk assessment on biodiversity is the same, although some additional considerations are derived from the biological characteristics peculiar to plantation trees, such as long lifespan, large size, and wide ecological interaction, as well as from traits peculiar to plantation trees, such as modification of lignin content or quality (CBD-COP-MOP8 2016; Häggman et al. 2013).

Eucalyptus trees currently are the most important forestry plantation trees. The genus Eucalyptus consists of more than 600 species of flowering trees and shrubs, most of which are native to Australia, with additional species found in Papua New Guinea, Indonesia, and on the island of Mindanao in the Philippines (Nishimura 1987). Eucalyptus camaldulensis Dehnh., with the common name River red gum, is one of nine species of fast-growing Eucalyptus trees that are found on plantations all over the world. Previously, the development of transgenic E. camaldulensis trees was reported (Chen et al. 2001; Harcourt et al. 2000; Ho et al. 1998; Kawaoka et al. 2006; Mendonça et al. 2013; Mullins et al. 1997; Valério et al. 2003). An environmental risk assessment of transgenic E. camaldulensis has also been reported (Kikuchi et al. 2006, 2009; Yu et al. 2013b). Moreover, field trials were conducted under type 1 use approvals by the Japanese Ministry of Education, Culture, Sports, Science, and Technology and by the Japanese Ministry of the Environment.

The choline oxidase A (codA) gene, derived from the soil bacterium Arthrobacter globiformis, codes an enzyme catalyzing the reaction to synthesize glycine betaine, which functions as an osmotic protectant in organelles and cytosol (Ashraf and Foolad 2007; Chen and Murata 2008, 2011; Giri 2011; Kurepin et al. 2015; Sakamoto and Murata 2002). We have developed the transgenic E. camaldulensis and E. globulus harboring the codA gene. We also conducted environmental risk assessments of these transgenic Eucalyptus trees on productivities of harmful substances to affect soil microorganisms and/or other plants by special-netted house cultivation and isolated field trials. The results showed no significant differences between non-transgenic and transgenic Eucalyptus trees regarding potential impacts on the biodiversity of both soil microorganisms and other plants (Kikuchi et al. 2006, 2009; Oguchi et al. 2014; Yu et al. 2013a, 2013b). In this study, we assessed the potential impact on biodiversity of four novel transgenic E. camaldulensis harboring the codA gene, i.e., codAH-1, codAH-2, codAN-1, and codAN-2, which we reported recently (Tran et al. 2018). The codAH and codAN transgenic trees were different in terminator sequences for codA transcription, i.e., HSP terminator and NOS terminator, respectively (Figure 1). The transcriptional levels of codA in codAHs were more than fourfold higher than codANs (Tran et al. 2018). The accumulation levels of glycine betaine in codAHs were more than 1.7- and 40-fold higher than codANs non-transgenic lines, respectively (Tran et al. 2018).

Figure 1. Schematic diagrams of the T-DNA region of codAH and codAN. codA, a choline oxidase gene derived from A. globiformis; 35S pro, CaMV 35S promoter; NOS ter, nopaline synthase terminator; HSP ter, heat-shock protein 18.2 terminator; ADH UTR, A. thaliana ADH transcriptional enhancer; CP, N. tabacum rbcS chloroplast transit peptide; NPTII, neomycin transferase II; CDA, cytosine deaminase A; NOS pro, nopaline synthase promoter; R, specific recombination site of Zygosaccharomyces rouxii recombinase R; RB and LB, right and left border.

Figure 1. Schematic diagrams of the T-DNA region of codAH and codAN. codA, a choline oxidase gene derived from A. globiformis; 35S pro, CaMV 35S promoter; NOS ter, nopaline synthase terminator; HSP ter, heat-shock protein 18.2 terminator; ADH UTR, A. thaliana ADH transcriptional enhancer; CP, N. tabacum rbcS chloroplast transit peptide; NPTII, neomycin transferase II; CDA, cytosine deaminase A; NOS pro, nopaline synthase promoter; R, specific recombination site of Zygosaccharomyces rouxii recombinase R; RB and LB, right and left border.

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The biodiversity impact of transgenic plants is basically evaluated on the substantial equivalence concept and by the familiarity of the plant species. The Japanese government defines an impact on biodiversity as an “adverse effect that could pose an unacceptable risk of impairment to the preservation of species or populations of wild fauna or flora or any other Adverse Effect on Biological Diversity” (MAFF 2013; MoE 2013). Specifically, evaluation data on the potential risks regarding the following three points must be submitted in order to obtain approval for a Type 1 Use (field trial): “competition with native species”, “hybridization with native wild species”, and “producing harmful substances”. Moreover, regarding the potential damage caused by harmful substances, it is necessary to submit experimental data as instructed in Notifications from the Ministry of Agriculture, Forestry, and Fisheries, and from the Ministry of the Environment of Japan (MAFF 2013; MoE 2013); i.e., “Productivity of harmful substances (secretion from roots to affect the other plants)”, “Productivity of harmful substances (secretion from roots to affect microorganisms in soil)”, and “Productivity of harmful substances (substances in the plant body to affect the other plants after dying out)”.

In this study, we evaluated the substantial equivalence of four clonal lines of transgenic E. camaldulensis harboring the codA gene, i.e., codAH-1, codAH-2, codAN-1, and codAN-2, which are described in previous reports, to the conventional E. camaldulensis in the possible damage caused by harmful substances. We cultivated the four transgenic clonal lines and three independent non-transgenic clonal lines, i.e., cam2, cam6, and CML2, in 15-cm-diameter pots in a special netted house located in Tsukuba, Japan, for 6 months or more. Bioassay methods were used to evaluate the damage caused by harmful substances. The plant materials and cultivation conditions were described in detail previously (Tran et al. 2018).

The potential impacts on the ability of harmful substances secreting from the roots to affect other plants were evaluated by the succeeding crop assay (Atosaku assay) as described in previous reports (Asakawa et al. 1992) Soil samples were collected from pot-cultivated transgenic or non-transgenic E. camaldulensis trees for 6 months or more, and the growth of germinated lettuce seedlings sown on the soil was examined (Asakawa et al. 1992). The measurements were compared between the codAH lines and non-transgenic control lines and between the codAN lines and non-transgenic control lines, by analysis of variance (ANOVA) and Tukey’s honestly significant difference (HSD) test. The results of static testing by ANOVA revealed no significant difference in impacts on tested lettuce seedlings between each combination of transgenic and non-transgenic groups or among the lines (α=0.05; Table 1). The results of Tukey’s HSD test agreed with these results (Supplementary Figure S1). Thus, there was no significant difference between the transgenic and non-transgenic lines in potential impacts on productivities of harmful substances secreting from the roots to affect other plants.

Table 1. Analyses of variance of measurements of the succeeding crop assay.

Comparisona Testing object Source Dfb Sum Sqc F valued Pr(>F)e
codAH×NT Hypocotyle length TGf 1 0.00375 1.6972 0.2219 nsh
Lg 3 0.0045589 0.6878 0.5798 nsh
Residuals 10 0.0220953
Radicle length TGf 1 0.019953 3.8268 0.07893 nsh
Lg 3 0.01501 0.9596 0.44898 nsh
Residuals 10 0.052139
codAN×NT Hypocotyle length TGf 1 0.0020167 0.7878 0.3956 nsh
Lg 3 0.0117056 1.5242 0.2680 nsh
Residuals 10 0.0256
Radicle length TGf 1 0.0006 0.0781 0.7856 nsh
Lg 3 0.007106 0.3081 0.8191 nsh
Residuals 10 0.076867
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aAnalyses were performed by the ANOVA function in the CAR package (ver.2.1-6) of R software (ver. 3.4.2). bDegrees of freedom. cSum of squares. dVariance ratio against error. eProbability of F-value. fTested difference between the transgenic and non-transgenic groups. gTested difference among the five lines. hNot significant (α=0.05).

To evaluate potential impacts on productivities of harmful substances secreting from the roots to affect microorganisms in soil, the culturable aerobic microorganisms were counted by using two kinds of culture media; oxytetracycline-glucose-yeast extract (OGYE) medium and peptone-tryptone-yeast extract-glucose (PTYG) medium were used to count fungi and bacteria, respectively. The collected soil samples were suspended in 15 mM phosphate buffer (pH 7.0), and the diluted supernatants were spread onto OGYE or PTYG agar medium plates. After 3 or 7 days’ incubation in the dark at 25°C for OGYE or PTYG, the formatted colonies were counted. The colony number on PTYG medium after wiping the surface with 70% ethanol were taken as actinomycetes. The measurements were compared between the codAH lines and non-transgenic control lines and between the codAN lines and non-transgenic control lines by ANOVA and the HSD test, respectively. Static testing by ANOVA revealed no significant difference in impacts on the populations of culturable fungi, actinomycetes, and other bacteria between each combination of transgenic and non-transgenic groups or among the lines (α=0.05; Table 2). The Tukey’s HSD results agreed with those results (Supplementary Figure S2). Thus, there was no significant difference between the transgenic and non-transgenic lines in potential impacts on productivities of harmful substances secreting from the roots to affect adjacent soil microorganisms.

Table 2. Analyses of variance of numbers of culturable soil microorganism.

Comparisona Testing object Source Dfb Sum Sqc F valued Pr(>F)e
codAH×NT Actinomyces TGf 1 0.019267 1.3275 0.276 nsh
Lg 3 0.100689 2.3126 0.138 nsh
Residuals 10 0.145133
Bacteria (exc. Actinomyces) TGf 1 0.05415 4.8406 0.05243 nsh
Lg 3 0.10096 3.0082 0.08126 nsh
Residuals 10 0.11187
Fungus TGf 1 0.0024 0.3237 0.5819 nsh
Lg 3 0.024172 1.0869 0.3987 nsh
Residuals 10 0.074133
codAN×NT Actinomyces TGf 1 0.045067 2.7934 0.1256 nsh
Lg 3 0.042172 0.8713 0.4878 nsh
Residuals 10 0.161333
Bacteria (exc. Actinomyces) TGf 1 0.05415 2.851 0.1222 nsh
Lg 3 0.016222 0.2847 0.8354 nsh
Residuals 10 0.189933
Fungus TGf 1 0.004817 0.4807 0.5039 nsh
Lg 3 0.054972 1.8287 0.2056 nsh
Residuals 10 0.1002
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aAnalyses were performed by the ANOVA function in the CAR package (ver.2.1-6) of R software (ver. 3.4.2). bDegrees of freedom. cSum of squares. dVariance ratio against error. eProbability of F-value. fTested difference between the transgenic and non-transgenic groups. gTested difference among the five lines. hNot significant (α=0.05).

The potential impacts on productivities of harmful substances in the plant body to affect other plants after dying out were evaluated by the sandwich assay. Fresh leaves collected from all four transgenic and non-transgenic E. camaldulensis trees for 6 months cultivation or more were dried at 60°C for 24 h. Then, 10 mg or 50 mg of dried leaf tissue was embedded in low-melting-point agar (0.5% w/v) and the growth of germinated lettuce seedlings sown on the agar was examined (Fujii et al. 1992). The measurements were compared among the four transgenic lines and non-transgenic control lines by ANOVA and Tukey’s HSD test. ANOVA indicated a significant difference between the dosage (10 and 50 mg) of the leaf tissue, but no significant difference was observed in impacts on tested lettuce seedlings between the respective codAH- or codAN-transgenic groups and the non-transgenic groups (α=0.05; Table 3). Among the seven lines, a significant difference was observed in radicle growth (α=0.05; Table 3). However, this difference was not due to a difference in transgenes but due to errors, as supported by the result of Tukey’s HSD test (Table 3 and Supplementary Figure S3). These results indicated that there was no significant difference in potential impacts on productivities of harmful substances in the plant body to affect other plants after dying out between the transgenic and non-transgenic lines.

Table 3. Analyses of variance of measurements of the sandwich assay.

Testing objecta Source Dfb Sum Sqc F valued Pr(>F)e
Hypocotyl length Gf 2 0.03006 1.1072 0.3445 nsi
Lg 4 0.05321 0.9798 0.4344 nsi
Dh 1 1.36368 100.4409 9.168e-11 ***j
L : D 6 0.01274 0.1564 0.9861
Residuals 28 0.38015
Radicle length Gf 2 0.0178 1.0363 0.3680 nsi
Lg 4 0.1079 3.1362 0.0299 *k
Dh 1 4.1838 486.5543 <2e-16 ***j
L : D 6 0.1291 2.5023 0.0458 *k
Residuals 28 0.2408
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aAnalyses were performed by the ANOVA function in the CAR package (ver.2.1-6) of R software (ver. 3.4.2). bDegrees of freedom. cSum of squares. dVariance ratio against error. eProbability of F-value. fTested difference among codAHs, codANs, and non-transgenic groups. gTested difference among the seven lines. hTested difference between the dosages of input leaf tissues. iNot significant at an alpha level of 0.05. jSignificant differences at an alpha level of 0.001. kSignificant differences at an alpha level of 0.05.

In this study, we confirmed there was no significant difference between transgenic E. camaldulensis harboring codA and non-transgenic E. camaldulensis in their potential impacts on productivities of harmful substances to affect other plants and soil microorganisms. From these results, we concluded that the four transgenic E. camaldulensis clonal lines were substantially equivalent to non-transgenic E. camaldulensis regarding damage done to other plants and soil microorganisms by harmful substances. We have already confirmed that other transgenic Eucalyptus lines harboring the codA gene (E. camaldulensis and E. globulus) are also substantially equivalent to nonrecombinant in the damage potential of harmful substances (Kikuchi et al. 2006, 2009; Oguchi et al. 2014; Yu et al. 2013a). These results would suggest that improving the salt tolerance of the Eucalyptus genus by transformation of the codA gene does not affect productivities of harmful substances to affect biodiversity.

Acknowledgments

This research was supported in part by the New Energy and Industrial Technology Development Organization (NEDO) of Japan (P07015), and by a grant from the Plant Transgenic Design Initiative (PTraD), Gene Research Center, University of Tsukuba, Japan.

Abbreviations

codA

choline oxidase A

CBD

Convention on Biological Diversity

ERA

environmental risk assessment

ANOVA

analysis of variance

Supplementary Data

Supplementary Data

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plantbiotechnology-35-4-18.0831a-s001.pdf (650.3KB, pdf)
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