May 26, 2010

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Male sterility, cold resistance and modified lignin content

Release of genetically modified eucalyptus approved

In mid-May, the US Department of Agriculture (USDA) approved field trials with 200,000 genetically modified eucalyptus trees at 29 sites in seven states. The trials are testing three new traits: male sterility to prevent pollen spread, cold resistance to extend cultivation to more northern regions of the USA, and a lower lignin content. According to information provided by the manufacturer, ArborGen, the trees are intended to provide raw materials for paper and biodiesel production.

The USDA permit allows the company to plant over 200,000 genetically modified eucalyptus trees at sites in Alabama, Florida, Georgia, Louisiana, Mississippi, South Carolina and Texas on a total of 120 hectares.

The aim of the trials is to test the performance of the transgenic trees under field conditions at various sites and to check how well the biological containment concept works.

With the help of a cold-resistance gene, the trees are designed to be able to withstand temperatures as low as -8 °C. Conventional eucalyptus trees cannot at present be grown further north than Florida because of their sensitivity to the cold. Another gene construct is designed to lower the lignin content in the wood to make it more suitable as raw material for the paper industry. The gene construct also contain the nptII marker gene that causes kanamycin resistance.

Finally, the trees contain a genetically transferred barnase gene designed to make them male-sterile. The barnase enzyme breaks down RNA, which disrupts protein biosynthesis and causes the cells in question to die. A specific promotor ensures that the barnase gene is only active in the pollen-producing cells in the anthers. This is designed to prevent pollen production and minimize the risk of outcrossing.

Smaller trials conducted by ArborGen in previous years were approved on condition that the trees were not allowed to flower. For the latest trial, the USDA has said that the male-sterile trees can be allowed to flower on 28 of the 29 sites.

Approval heavily criticised

Nature conservation groups in particular have reservations about the trials. Cold-resistant trees could, they believe, spread more easily in the environment and become invasive species. It is also argued that the barnase protein is toxic to mammals and birds. Regardless of the safety concerns surrounding the GM trees, environmental groups like the Sierra Club are against eucalyptus plantations in general. They criticise the high water consumption of the plantations and the increased risk of forest fires. They claim that devastating forest fires have already been caused in Australia, for instance, by the high oil content of the trees. Camilia Moreno of the Global Justice Ecology Project points to negative experiences in Brazil. Here, she claims, eucalyptus plantations are ‘green deserts’ without undergrowth or wildlife. More than 12,000 objections to the trials were submitted to the USDA.

However, the USDA’s assessment comes to a different conclusion. The barnase gene is, it claims, only active in a small cell layer in the anthers and is broken down rapidly once the cells have been disabled. The protein does not accumulate in the trees.

Neither does the USDA think that the trees are likely to spread uncontrollably. The effectiveness of the pollen sterility has, it claims, been demonstrated in previous trials in Alabama, where the cold-tolerant eucalyptus trees had been unable to produce any functional pollen. In any case, they argue, the genetically modified eucalyptus trees would find it difficult to become established in the environment without human cultivation. The individual trial plots are small and far enough away from other eucalyptus trees to prevent outcrossing.

The current permit for the trials is valid for three years, after which the company will be seeking commercial approval for the GM eucalyptus trees.