Safety evaluation of environmental release of transgenic Populus tomentosa with AhDREB1 gene after 14 years of subculture

Objective This study used transgenic plants that had been subcultured for 14 years and subsequently grown in field conditions in Tianjin and Hebei of northern China for 6 years as research materials. The assessment covered multiple aspects including growth adaptability, gene expression stability, horizontal gene transfer potential, impact on soil environment, and allelopathic effects of rhizosphere soil extracts. The study systematically evaluated the stability and safety of transgenic P. tomentosa for AhDREB1 gene after long-term subculture and field release. The aim of this research was to provide long-term monitoring data from field trials of transgenic trees, thereby offering scientific support for the subsequent application and promotion of transgenic woody plants.

Method The growth status of transgenic P. tomentosa was analyzed by measuring its growth indicators such as tree height, DBH, and volume in the experimental forests on saline-alkali research sites in Tianjin Binhai and Hebei Cangzhou. After extracting total DNA from leaves, soil, and microorganisms, PCR technology was used to determine expression stability of exogenous genes in transgenic P. tomentosa and to explore the impact of exogenous genes on soil environment. The dilution plate counting method was adopted to analyze the quantity of soil microorganisms in different months. The allelopathic effect of root exudates from transgenic poplars on the growth of radicle and hypocotyl of Chinese cabbage (Brassica pekinensis) seeds was detected using rhizosphere soil extracts.

Result (1) The growth of transgenic P. tomentosa for AhDREB1 gene in the Tianjin Binhai and Hebei Cangzhou saline-alkali research sites was better than that of the non-transgenic lines. (2) The exogenous gene AhDREB1 still stably existed in the transgenic poplar through 14 years of subculturing and 6 years of field cultivation. No transfer of exogenous gene to soil and soil microorganisms was detected. (3) In different seasons, there was no significant difference in the quantity of soil microorganisms between the transgenic P. tomentosa for AhDREB1 gene and control. Additionally, the extracts of their rhizosphere soils showed no significant differences in their effects on the growth of radicles and hypocotyls of Chinese cabbage seeds.

Conclusion Under saline-alkali soil conditions, transgenic P. tomentosa for AhDREB1 gene exhibites significantly enhanced growth adaptability compared with non-transgenic P. tomentosa. Moreover, the AhDREB1 gene was stably expressed in perennial plants, and no potential ecological security risks to the environment caused by P. tomentosa transgenic for the AhDREB1 gene were observed. The results of this study will lay a scientific foundation for promotion and application of this transgenic line in saline-alkali environments.