Physiology and phytoremediation
During the period 2013-2018, a total of 156.5 hectares of poplar plantation was established in the Saemangeum reclaimed tideland for rehabilitation as well as wood production. Populus euramericana, P. deltoides and Populus alba x Populus tremula var. glandulosa were planted. In the test plot of the plantation, A P. deltoides clone performed best and produced the above ground dry weight of around 6 tons per hectare in the first year. In the second and the third year, the production reached 9.33 and 13.73 tons per hectare per year, respectively.
The physiological characteristics of poplars on salty reclaimed soil with poor drainage were determined with P. euramericana and P. deltoides clones. Overall, P. euramericana clones were better than P. deltoides hybrid clones especially in the net photosynthetic rate. In contrast, the total chlorophyll and carotenoid contents were higher in P. deltoides hybrid clones than P. euramericana clones in July. The physiological activities such as net photosynthetic rate and stomatal conductance of P. deltoides hybrid clones were much lower in August than in July. The results suggested that P. euramericana Venziano clone was better adapted to the soil with poor drainage than were the other clones tested in Saemanguem area.
A short rotation coppice plantation consisting of 2-year old poplar clones was established in a riparian area to select the most suitable clones for biomass. Biomass production, nitrogen and carbon absorption were determined in Populus deltoides hybrid clone 97-18, P. euramericana clone Eco28 and P. alba x P. tremula var. glandulosa clone 72-30. The average number of stems per stump was five and P. euramericana clone Eco28 had the greatest average number of live stems per stump with 5.9. The average stem diameter of all clones was 23.2 mm, and P. deltoides hybrid clone 97-18 showed the largest average diameter with 25.4 mm. The average annual above-ground biomass was 16.1 tons per hectare per year for P. deltoides hybrid clone 97-18, followed by 12.3 tons for P. alba x P. tremula var. glandulosa clone 72-30 and 5.4 tons for P. euramericana clone Eco28. The average annual nitrogen uptake of the clones was 46.5 kg per hectare per year. P. alba x P. tremula var. glandulosa clone 72-30 absorbed as much as 63.1 kg nitrogen per hectare per year. As for carbon absorption, P. deltoides hybrid clone 97-18 showed the best results with 7.7 tons of carbon per hectare per year.
Genetics and genetic engineering
Although poplars are not being intensively cultivated in Korea, genetics research is actively carried out with the species. The complete chloroplast genomes of Populus alba x P. tremula var. glandulosa and Populus davidiana were determined in 2019. The complete mitochondrial genome of Populus alba x P. tremula var. glandulosa was also fully revealed. Interestingly, a Lab at the University Arizona in the US published the full genome sequence of Populus alba x Populus tremula var. glandulosa clone 84K (Qiu et al. 2019). According to the report, Populus alba x P. tremula var. glandulosa genome is composed of two subgenomes, representing 356 Mb from P. alba (subgenome A) and 354 Mb from P. tremula var. glandulosa (subgenome G).
The complete mitochondrial genome of tulip tree (Litiodendron tulipifera) was determined in 2019. It has 156,387 base pairs of DNA with 66 genes.
Many nuclear genes have been isolated from Populus alba x Populus tremula var. glandulosa and their functions were determined through gene expression analysis mostly using transgenic plants. These include MYC2 gene in relation to leaf senescence response, Dormancy-associated protein 1 gene involved in abiotic stress tolerance, R2R3-MYB transcription factor that promotes anthocyanin production.
Several transgenic poplar clones were also developed. Most of the traits they transferred are related to either biomass growth or stress tolerance in Populus alba x Populus tremula var. glandulosa. The transgenic poplar expressing a gibberellin 20-oxidase 1 gene from Pinus densiflora improved biomass production. A remarkable development of gene expression technology was made by bicistronically expressing both wood forming tissue-specific PdGA20ox1 and PtrMYB221 genes in poplar. The transgenic poplars showed improvement in both the quality and quantity of woody biomass. A novel xylem tissue specific promoter from Populus trichocarpa was screened and evaluated in transgenic Populus alba x Populus tremula var. glandulosa. Since the promoter activity is exclusively in mature xylem tissue, it may offer an effective means to improve the chemical and physical properties of the wood. Transgenic Populus alba x Populus tremula var. glandulosa expressing the constitutively active small G protein showed increased stem growth and produced 3–4 times greater dry biomass than hybrid control poplars. Fiber length and diameter were also increased by 15–26% and 28–38%, respectively. As for stress tolerance, the down-regulated GIGANTEA-like gene in transgenic poplar increased plant growth and salt stress tolerance.
Literature cited
Bae EK, YI Choi, H Lee, JW Choi (2019). Isolation and characterization of Auxin/indole-3-acetic acid 1 (Aux/IAA1) gene from poplar (Populus alba × P. glandulosa). J Plant Biotechnol. 46:180-188
Chandra R, H Kang (2018) Phytoremediation and physiological effects of mixed heavy metals on poplar hybrids. DOI: 10.5772/intechopen 76348
Chandra R, W Cho, H Kang (2016). Phytoextraction potential of four poplar hybrids under greenhouse conditions. Forest Science and Technol. 12: 1-8. 10.1080/21580103.2016. 1180325
Cho JS, HW Jeon, MH Kim, K. Vo, J Kim, EJ Park, YI Choi, H Lee, K-H Han, J-H Ko (2018) Wood forming tissue-specific bicistronic expression of PdGA20ox1 and PtrMYB221 improves both the quality and quantity of woody biomass production in a hybrid poplar. Plant Biotechnol. J. 17: 1048~1057
Cho JS , SA Noh, YI Choi (2016) Characterization of a non-specific Lipid Transfer Protein (ns-LTP) promoter from poplar (Populus alba x P. glandulosa). J. Plant Biotechnol. 42: 356-363.
Cho JS, VP Nguyen, HW Jeon, MH Kim, SH Eom, YJ Lim, WC Kim, EJ Park, YI Choi, JH Ko (2016). Overexpression of PtrMYB119, a R2R3-MYB transcription factor from Populus trichocarpa, promotes anthocyanin production in hybrid poplar. Tree Physiol. 36:1162-76.
Choi, H, EK Bae, J Cho, H Lee, YI Choi (2017) Identification and characterization of the MYC2 gene in relation to leaf senescence response in hybrid poplar (Populus alba × P. glandulosa). J. Plant Biotechnol. 44: 409-415. 10.5010/JPB.2017.44.4.409.
Choi H, EK Bae, YI Choi, SK Yoon, H Lee (2017) Characterization of Gibberellic Acid-Stimulated Arabidopsis (GASA) gene to drought stress response in Poplar (Populus alba × P. glandulosa). J Plant Biotechnol. 44:61–68
Choi MN, M Han, HS Park, MY Kim, JS Kim, YJNa, SW Sim, EJ Park (2016) The complete chloroplast genome sequence of Populus davidiana Dode. Mitochondrial DNA Part B 1: 674-675
Ganchudur T, A Khaulenbek, W Cho, S Lee, R Chandra, J Cho, W Chia, Rogers & H Kang, (2018). Effects of Oxidized Brown Coal Humic Acid Fertilizer on the Relative Height Growth Rate of Three Tree Species. Forests 9: 360. 10.3390/f9060360.
Jang JH, SH Kim, I Khaine, MJ Kwak, HK Lee, TY Lee, WY Lee, SY Woo (2018) Physiological changes and growth promotion induced in poplar seedlings by the plant growth-promoting rhizobacteria Bacillus subtilis JS. Photosynthetica 56: 1188–1203
Jeon HW, JS Cho, EJ Park, KH Han, YI Choi, JH Ko (2016) Developing-xylem preferential expression of PdGA20ox1, a gibberellin 20-oxidase1 from Pinus densiflora, improves woody biomass production in a hybrid poplar. Plant Biotechnol. J. 14: 1161-1170.
Jin, X, Y Kim (2019) Taxonomic Study of Populus maximowiczii Henry and Populus koreana Rehder based on Morphological Characters. J. Agriculture & Life Sci. 53:77-85
Kang MS, KS Jang, YM Son, RH Kim, IH Park, KH Lee (2016). Allometric Equations and Biomass Expansion of Yellow Poplar (Liriodendron tulipifera) in Southern Korea. J. Kor. For. Soc.105: 463-471
Ke Q, HS Kim, Z Wang, CY Ji, JC Jeong, H-S Lee, Y‐I Choi, B Xu, X Deng, D‐J Yun, S‐S Kwak (2016). Down‐regulation of GIGANTEA‐like genes increases plant growth and salt stress tolerance in poplar. Plant Biotech J. https://doi.org/10.1111/pbi.12628
Kim, HC, SJ Lee, WY Lee, JW Kang (2016) Selection of Poplar Clones for Short Rotation Coppice in a Riparian Area. Journal of Korean Society of Forest Sci. 105:103-107
Kim MH, JS Cho, HW Jeon, K Sangsawang, D Shim, YI Choi, EJ Park, H Lee, JH Ko (2019) Wood Transcriptome Profiling Identifies Critical Pathway Genes of Secondary Wall Biosynthesis and Novel Regulators for Vascular Cambium Development in Populus. Genes 10: 690
Kim MH, JS Cho, JH Lee, SY Bae, YI Choi, EJ Park, H Lee, JH Ko (2018) Poplar MYB transcription factor PtrMYB012 and its Arabidopsis AtGAMYB orthologs are differentially repressed by the Arabidopsis miR159 family. Tree Physiol. 38: 801–812
Kim NY, HS Jeon, MH Lee, A Cha, DS Lee, HJ Lee, HG Kim, H Lee, YI Choi, O Kim (2018). Field evaluation of transgenic poplars expressing the constitutively active small G protein for improved biomass traits. Biomass and Bioenergy 10: 16-22
Kim YW, JW Kang, HK Moon (2016) Somatic embryogenesis and plant regeneration of yellow poplar (Liriodendron tulipifera L.) at National Institute of Forest Science. 10.13140/RG.2.1.2325.4803.
Lee H, HC Kim, JW Kang, WY Lee, H Lim, K Jang (2018). Selection of Poplar Clones for Short Rotation Coppice in a Reclaimed Land. J Agriculture & Life Sci. 52: 21-32
Lee JK, JH Jang, L Yang, HN Kim, MJ Kwak, Ik Khaine, TY Lee, HK Lee, IR Kim, GH Jang, WY Lee (2017), Physiological Characteristics of Poplar Clones in the Saemanguem Reclaimed Land. J. Korean For. Soc. 106: 186-195
Lee KM, YY Kim, JO Hyun (2011) Genetic variation in populations of Populus davidiana Dode based on microsatellite marker analysis. Genes and Genomics 33: 163-171
Lee MW, KN Hong, YJ Park, J W Lee, HI Lim (2016). Fine-scale Spatial Genetic Structure of a Small Natural Stand of Populus davidiana in South Korea using AFLP markers. J. Korean For. Soc. 105: 309-314
Nguyen VP, JS Cho, YI Choi, SW Lee, KH Han, JH Ko (2016). Evaluation of a novel promoter from Populus trichocarpa for mature xylem tissue specific gene delivery. Plant Physiol Biochem. 104: 226-233.
Park J, Y Kim, H Xi, W Kwon, M Kwon (2019). The complete chloroplast and mitochondrial genomes of Hyunsasi tree, Populus alba x Populus glandulosa (Salicaceae). Mitochondrial DNA Part B 4:
Park J, Y Kim, H Xi, W Kwon, M Kwon (2019). The complete mitochondrial genome of tulip tree, Liriodendron tulipifera L. (Magnoliaceae): intra-species variations on mitochondrial genome. Mitochondrial DNA Part B
Qiu D, S Bai, J Ma, L Zhang, F Shao, K Zhang, Y Yang, T Sun, J Huang, Y Zhou, DW Galbraith, Z Wang, G Sun (2019) The genome of Populus alba x Populus tremula var. glandulosa clone 84K. DNA Research 26: 423–431,
Yoon SK, EK Bae, H Choi, YI Choi, H Lee (2017) Isolation and Expression of Dormancy-associated protein 1 (DRM1) in Poplar (Populus alba × P. glandulosa). J Plant Biotechnol. 44: 9969–75