Abstract
Poplar is one of the main afforestation tree species in China, and the use of a single, or only a few, clones with low genetic diversity in poplar plantations has led to increasing problems with insect pests. The use of genetic engineering to cultivate insect-resistant poplar varieties has become a hot topic. Over the past 20 years, there have been remarkable achievements in this area. To date, nearly 22 insect-resistant poplar varieties have been created and approved for small-scale field testing, environmental release, or pilot-scale production. Here, we comprehensively review the development of insect-resistant genetically modified (GM) poplars in China. This review mostly addresses issues surrounding the regulation and commercialization of Bt poplar in China, the various insecticidal genes used, the effects of transgenic poplars on insects, toxic protein expression, multigene transformation, the stability of insect resistance, and biosafety. The efficacy of GM poplars for pest control differed among different transgenic poplar clones, larval instars, and insect species. The Bt protein analysis revealed that the expression level of Cry3A was significantly higher than that of Cry1Ac. Temporal and spatial studies of Bt protein showed that its expression varied with the developmental stage and tissue. The inheritance and expression of the exogenous gene were reviewed in transgenic hybrid poplar progeny lines and grafted sections. Biosafety issues, in terms of transgene stability and the effects on soil microorganisms, natural enemies of insects, and arthropod communities are also discussed.
Highlights
Since the first report on transformation of Bt gene into Populus nigra was published in 1991, transgenic approaches have been widely used in breeding trees for insect resistance and other environmental stress tolerance in China
In the above study on poplar, Enzyme-linked immunosorbent assay (ELISA) analysis showed that accumulation of Bt protein was highest in phloem tissues, indicating that Bt protein was mainly translocated within the phloem across the graft union to the leaves
Reverse transcription-polymerase chain reaction (PCR) (RT-PCR) showed that mRNA of Bt gene was not detected in the branch and leaf of nontransgenic poplar 741 no matter its material was used as scion or stock, which suggested that mRNA of Bt gene was not transported between the stock and scion (Wang and Yang, 2010)
Summary
Since the first report on transformation of Bt gene into Populus nigra was published in 1991, transgenic approaches have been widely used in breeding trees for insect resistance and other environmental stress tolerance in China. Research on GM poplars in China commenced in the early 1990s; the first milestone was transformation of the Bt gene into P. nigra (Wu and Fan, 1991) Research efforts in this area continued focusing on white and black poplars and various hybrids After two decades of study, there have been remarkable achievements in the fields of insecticidal gene transfer, toxin expression and transportation, multigene transformation, insect resistance sustainability and stability, and biosafety. The State Forest Administration (SFA) has established several regulatory frameworks for forest genetic engineering; all research on insect-resistant trees must follow certain procedures in terms of project application and approval, small-scale field testing, environmental release, pilot-scale production, and commercialization, each phase must be evaluated by experts (Lu and Hu, 2011). The Chinese government has adopted a cautious attitude; many other insect-resistant poplar varieties have been obtained following development of the two above-mentioned varieties, no new commercial trees have been approved
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