Background: Soil heavy metal pollution by chromium (Cr) and copper (Cu) is a global environmental concern. Methods: This study evaluated Cr/Cu accumulation in Paulownia fortunei tissues and analyzed its root transcriptome under Cr and Cu stress to elucidate molecular response mechanisms. Results: Findings revealed significantly higher Cr and Cu accumulation capacity in roots compared to stems and leaves. Transcriptome sequencing identified 6017 and 2265 differentially expressed genes (DEGs) under Cr and Cu stress, respectively. These DEGs were primarily involved in redox reactions, stress responses, transcriptional regulation, transmembrane transport, and metabolism. Quantitative PCR of 20 selected genes validated dynamic expression changes under stress. Weighted Gene Co-expression Network Analysis (WGCNA) identified distinct co-expression modules associated with Cr and Cu. Hub gene analysis implicated Pfo_020668 and Pfo_019190 in Cr response, while Pfo_010312 and Pfo_000197 may enhance Cu tolerance via cell wall polysaccharide synthesis regulation. Pathways related to pyruvate metabolism and proteasome were significantly enriched under Cr stress, whereas amino acid metabolism pathways were prominent under Cu stress. Conclusions: Differentially expressed transporter genes suggest potential roles in heavy metal uptake and transport. This transcriptomic analysis provides novel insights into P. fortunei’s molecular responses to Cr and Cu stress, offering a foundation for utilizing this species in soil phytoremediation efforts.

Keteleeria davidiana var. calcarea is an endangered plant endemic to China. It is mainly distributed in the karst areas of the Guangxi and Guizhou Provinces. It is characterized by small populations and intermittent distribution. This study aimed to explore the genetic diversity and mating system of wild populations of Keteleeria davidiana var. calcarea in fragmented habitats. To achieve this, we genotyped 46 maternal trees and 214 progenies from four fragmented populations of Keteleeria davidiana var. calcarea using nine pairs of microsatellite primers. The genetic diversity of Keteleeria davidiana var. calcarea (Ho = 0.68, He = 0.63) was lower than that of the species overall but higher than that of other Keteleeria plants. The incidence of unbiased expected heterozygosity (uHe) and allelic richness (Ar) was higher in the maternal generation than in the progeny. This suggests that the genetic diversity of the progeny was lower than that of the maternal generation. Keteleeria davidiana var. calcarea is divided into four populations, but there is significant genetic exchange between the populations according to STRUCTURE and gene flow analyses. The multilocus mating system analysis (MLTR) results indicate that the multilocus outcrossing rate (t_m) was 0.902, the single-locus outcrossing rate (t_s) was 0.606, the bimaternal inbreeding coefficient (t_m-t_s) was 0.295, and the coefficient of inbreeding depression(δ) was 0.904. These results suggest a certain degree of selfing and inbreeding in Keteleeria davidiana var. calcarea. To prevent problems associated with inbreeding and conserve the genetic diversity of Keteleeria davidiana var. calcarea, we recommend establishing seed gardens, using artificial pollination, and employing asexual propagation techniques for conservation intervention.