1-Deoxy-d-xylulose-5-phosphate synthase (DXS) is the rate-limiting enzyme in the plastidial methylerythritol phosphate pathway (MEP). In this study, PtDXS (XM_024607716.1) was isolated from Populus trichocarpa. A bioinformatics analysis revealed that PtDXS had high homology with the DXSs of other plant species. PtDXS expression differed among plant tissues and was highest in young leaves and lowest in roots. The recombinant protein was produced in Escherichia coli BL21 (DE3), purified, and its activity evaluated. The purified protein was capable of catalyzing the formation of 1-deoxy-d-xylulose-5-phosphate (DXP) from glyceraldehyde-3-phosphate and pyruvate. A functional color assay in E. coli harboring pAC-BETA indicated that PtDXS encodes a functional protein involved in the biosynthesis of isoprenoid precursors. The treatment of P. trichocarpa seedlings with 200 μM abscisic acid (ABA), 200 mM NaCl, 10% polyethylene glycol₆₀₀₀, and 2 mM H₂O₂ resulted in increased expression of PtDXS. The ABA and gibberellic acid contents of the transgenic lines (Poplar Nanlin 895) were higher than wild types, suggesting that DXS is important in terpenoid biosynthesis. Overexpression of PtDXS enhanced resistance to S. populiperda infection. Furthermore, the transgenic lines showed decreased feeding by Micromelalopha troglodyta, supporting the notion that PtDXS is a key enzyme in terpenoid biosynthesis.

Populus is a genus of globally significant plantation trees used widely in industrial and agricultural production. Poplars are easily damaged by Micromelalopha troglodyta and Hyphantria cunea, resulting in decreasing quality. Bt toxin-encoded by the Cry gene has been widely adopted in poplar breeding because of its strong insect resistance. There is still no comprehensive and sufficient information about the effects of Cry1Ah1-modified (CM) poplars on the ecological environment. Here, we sampled the rhizosphere soils of field-grown CM and non-transgenic (NT) poplars and applied 16S rRNA and internal transcribed spacer amplicon Illumina MiSeq sequencing to determine the bacterial community associated with the CM and NT poplars. Based on the high-throughput sequencing of samples, we found that the predominant taxa included Proteobacteria (about 40% of the total bacteria), Acidobacteria (about 20% of the total bacteria), and Actinobacteria (about 20% of the total bacteria) collected from the natural rhizosphere of NT and CM poplars. In addition, studies on the microbial diversity of poplar showed that Cry1Ah1 expression has no significant influence on rhizosphere soil alkaline nitrogen, but significantly affects soil phosphorus, soil microbial biomass nitrogen, and carbon. The results exhibited a similar bacterial community structure between CM varieties affected by the expression of Cry1Ah1 and non-transgenic poplars. In addition, Cry1Ah1 expression revealed no significant influence on the composition of rhizosphere microbiomes. These results broadly reflect the effect of the Bt toxin-encoded by Cry1Ah1 on the ecology and environment and provide a clear path for researchers to continue research in this field in the future.