Research and Application of Transgenic Poplar in China

Poplar is a major tree species used in both ecological and economic plantations in China. Notably, a total of 7.04 million hectares of selected poplar clones were planted in China for commercial production and shelter belts during the past 20 years, this represents a significant 19 % of total tree plantations in China. However, these mono-clonal plantations are facing damage by insect pests which caused severe infestations resulting in significant loss, estimated at millions of US dollars annually. In addition, it is estimated that by the year 2020, China will increase tree plantation by 40 million hectares and timber storage by 1.3 billion cubic meters in 2020. In order to meet this challenging goal, the development of tree plantations in northern dry and semi-dry areas is accelerated, poplar as a fast-growing candidate needs improvement of stress tolerance. Unfortunately, poplar plantation clones under these challenges are not easily solved by conventionally breeding techniques like hybridization and selection. Genetic engineering is one of the most powerful and promising technique to improve the tolerance of poplar clones being used in plantations. In order to develop poplars that were more tolerant to insect attack, GM/biotech poplars were developed in China. More specifically, Populus nigra clones (12, 172 and 153) were developed with cry1Aa and a hybrid white poplar, clone 741, was transformed with a fusion of cry1Aa and API (coding for a proteinase inhibitor from Sagittaria sagittifolia Under rigorous testing, the Bt poplar clones are exhibited a high level of resistance to leaf pests, resulting in a substantial 90 % reduction in leaf damage. The two clones were first commercialized in 2001 and by the year 2011, the transgenic poplars occupied 490 ha compared with 453 ha in 2010. The transgenic poplar plantations have effectively inhibited the fast-spread of target insect pests and have significantly reduced the number of insecticide applications required. The performance of the Bt black poplar plantations are significantly better than the clones deployed locally. Transgenic approaches have been also used in breeding trees for high tolerance to environmental stresses in China. Several transgenic poplars with tolerance of abiotic stresses has been reported, with two field testing cases showed a high salinity tolerance of transgenic poplar in marine salina. A hybrid poplar (P. simoni X P. deltoids) clone “Balizhuang” transformed with 1-p-mannitol dehydrogenase (mtlD) gene under 35S promoter were generated and the cuttings from this transgenic clone could survive in 0.4 % NaCl solution, and its seedlings gave a high survival rate and grew better in marine salina with 0.5 % salt concentration, comparing to non-transgenic clones. A much deployed hybrid clone (Populus X euramericana) ‘Guariento’ in plantation were transformed with multiple tolerance genes by biolistic bombardment and exhibited tolerance to drought and salinity, and field testing showed that the transgenic poplars perform well in harsh soil. Transgenic poplars aiming to change the wood property and the success in lowering the lignin content could improve the efficiency in pulping and saccharification of the wood. As of the end of 2010, 33 field trials had been approved and implemented featuring tolerance to insects, diseases, drought, and wood quality traits. The availability of commercial Bt poplar plantations has made it possible to empirically assess gene flow via pollen and seeds, and also for assessing the impact of Bt poplar on the insect community when intercropping with Bt cotton. The preliminary results showed generally no significant negative effects on the ecosystem. The transgenic Populus nigra has also been used for hybridizing with non-transgenic P. deltoides to generate an insect resistant source in a breeding program designed to generate new hybrid clones. The 2-year old hybrids are grew in nursery and the insect bioassay showed nearly ten times in decrease of weight and 60–100 % of mortality of Lymantria dispar L. larvae after feeding with hybrid leaves for 2 weeks. The better clones will be farther selected for field testing and expected to be used in a larger region since the P. deltoids is more suitable to the south region comparing to the P. nigra. The search for new genes or modification of available genes in further improvement of poplar clones with significant effects on their tolerance of biotic, abiotic stresses and quality of timber began about 10 years ago. Most studies are using transcript and protein profiling techniques like RNA-Seq, microarray and proteomic analysis during trait development in novel stress tolerance trees like P. euphratica, Tamarix androssowii, etc.. Several genes or gene clusters were used to further testing the usefulness of them in poplar breeding for stress tolerance. Modified available genes like Bt fused with activity enhancer or other genes to increase the stress tolerance are also in progress.