Clonal forestry has developed rapidly in recent years and already plays a significant role in commercial tree plantations worldwide. Clonal breeding requires accurate assessments of genetic parameters, together with measurements of clonal productivity, stability, and adaptably. However, relevant studies for clones of Paulownia spp. genotypes are rare. We therefore conducted clonal tests on twenty Paulownia clones established at three sites in the temperate and subtropical regions of China. Trees were planted in a randomized block design, with four replications in each site, twenty plots in each block, and six to eight individuals of the same clone in each plot. We measured the trunk diameter at breast height (DBH), total trunk height (H_t), and individual stand volume of 7-year-old trees to estimate genetic parameters and analyze genotype–environment interactions. A combined analysis of variance indicated that clonal, site, and clone–site interactions significantly affected the three growth traits. Clonal heritability and individual heritability were 0.35–0.84 and 0.07–0.30, respectively. The phenotypic and genetic correlation coefficients among the growth traits were 0.46–0.93 and 0.85–0.99, respectively. There were extremely significant positive linear relationships between the best linear unbiased predictors for DBH and the original DBH values (R² > 0.98). Clones 10, 2, 18, and 13 were selected for deployment based on a selection intensity of 1.4, GGE biplots, and the relative performance of harmonic means on genotypic values analysis. For these clones, the genetic gains in DBH, H_t, and volume were 18.05%, 21.46%, and 46.03%, respectively. These results provide useful information for the selection of Paulownia clones at the target sites and will provide a sound basis for improving Paulownia clonal breeding programs in the future.

Societal Impact Statement: Trees in the genus Paulownia play a crucial role in sustainable forestry, rural economic development, and carbon mitigation due to their rapid growth, exceptional hardwood properties, and prominent carbon sequestration capacity. This review highlights the societal value of Paulownia trees and synthesizes several potential drivers of extraordinarily fast growth in these trees. These insights are valuable for maximizing Paulownia 's potential for timber production and carbon sequestration, and they also provide a valuable model for studying mechanisms of rapid growth in hardwood trees. Summary: Paulownia is a genus of fast‐growing deciduous hardwood trees that are economically and ecologically important. Originally from East Asia, Paulownia are grown globally for their robust timber, agroforestry, and effective carbon dioxide drawdown, services that arise from their remarkably fast growth. Despite their clear value, the underlying drivers of fast growth in this genus remain poorly understood. Here, we review potential causes of fast growth in Paulownia and identify several potential adaptations, including photosynthetic metabolism, non‐foliar photosynthesis, tree habit, leaf structure, and hydraulic investment, that may contribute to fast growth in these trees. Our review highlights the paucity of evidence that would enable evaluation of these properties of Paulownia species and makes recommendations for future research needed to help explain drivers of fast growth in these important trees. In doing so, this review establishes a promising model system to study rapid growth in hardwood trees, their benefits to plantation cultivation, and potential for bioengineering.

Quantitative trait locus (QTL) mapping based on a genetic map is a very effective method of marker-assisted selection in breeding, and whole-genome resequencing is one of the useful methods to obtain high-density genetic maps. In this study, the hybrid assembly of Illumina, PacBio, and chromatin interaction mapping data was used to construct high-quality chromosomal genome sequences of Paulownia fortunei, with a size of 476.82 Mb, a heterozygosity of 0.52%, and a contig and scaffold N50s of 7.81 Mb and 21.81 Mb, respectively. Twenty scaffolds with a total length of 437.72 Mb were assembled into 20 pseudochromosomes. Repeat sequences with a total length of 243.96 Mb accounted for 51.16% of the entire genome. In all, 26,903 protein-coding gene loci were identified, and 26,008 (96.67%) genes had conserved functional motifs. Further comparative genomics analysis preliminarily showed that the split of P. fortunei with Tectona grandis likely occurred 38.8 (33.3–45.1) million years ago. Whole-genome resequencing was used to construct a merged genetic map of 20 linkage groups, with 2993 bin markers (3,312,780 SNPs), a total length of 1675.14 cm, and an average marker interval of 0.56 cm. In total, 73 QTLs for important phenotypic traits were identified (19 major QTLs with phenotypic variation explained ≥ 10%), including 10 for the diameter at breast height, 7 for the main trunk height, and 56 for branch-related traits. These results not only enrich P. fortunei genomic data but also form a solid foundation for fine QTL mapping and key marker/gene mining of Paulownia, which is of great significance for the directed genetic improvement of these species.

Paulownia trees are grown globally for their robust timber, agroforestry, and effective carbon dioxide drawdown. China possesses rich Paulownia germplasm resources, offering favorable material for the genetic improvement. Understanding the taxonomy and phylogenetic relationships of Paulownia species is essential for the advancement of germplasm innovation. In this study, we re-sequenced 67 typical accessions of 11 species within the Paulownia genus. A total of 16,163,790 high-quality single nucleotide polymorphisms (SNPs) were identified. Based on these markers, these accessions were classified into three groups: P. fortunei and P. lampropylla (Group I); P. tomentosa, P. fargesii, and P. kawakamii (Group II); and P. taiwaniana, P. jianshiensis, P. catalpifolia, P. elongata, P. ichangensis, and P. albiphloea (Group III). Using maximum likelihood estimation, population genetic structure analysis revealed that the 11 species originated from four different ancestral populations. The two predominant breeding species—P. fortunei and P. tomentosa—exhibit divergent origins: P. fortunei arose from hybridization between two ancestral species followed by complex admixture, whereas P. tomentosa retains a predominantly singular ancestral lineage, with traces of P. kawakamii. The genetic diversity (π) of P. tomentosa was 0.002588, which was considerably lower than that of P. fortunei (0.004181) suggesting that P. tomentosa is subjected to a stronger breeding selection during the evolution than P. fortunei. A total of 59 selected regions and 65 genes were identified by selective sweep analysis. These genes may be involved in biological processes such as morphological development and response to abiotic stress and hormonal activity regulation. These findings provide valuable references for further research on the genetic differentiation and adaptive evolutionary mechanisms of Paulownia species, laying a foundation for future germplasm innovation and variety improvement.

GENERAL REGULATORY FACTOR (GRF) proteins constitute an evolutionarily conserved family of phosphoserine/phosphothreonine-binding adaptors that orchestrate multiple signaling pathways governing plant development and adaptive responses to environmental cues. Here, we performed a genome-wide characterization of the GRF family in Paulownia fortunei, a commercially important fast-growing timber tree, and identified 15 PfGRF genes that are non-uniformly distributed across nine chromosomes. Phylogenetic reconstruction assigned these genes into two distinct clades, ε and non-ε, both characterized by conserved motif compositions and exon–intron structures. Promoter analysis uncovered a wide spectrum of cis-regulatory elements associated with hormone signaling and stress responses, and synteny examination revealed that segmental duplication, rather than tandem duplication, drove the expansion of this family, with the strongest collinearity detected against Populus trichocarpa. Expression profiling across eight organs demonstrated marked tissue-preferential patterns, with the majority of PfGRF transcripts most abundant in mature leaves and male buds. In addition, PfGRF1 was experimentally verified to localize to the nucleus. Functional assays further showed that PfGRF4–7 possess transcriptional self-activation capacity, whereas PfGRF15 does not, and yeast two-hybrid experiments confirmed a specific protein interaction between PfGRF4 and PfGRF5.