Plant breeders have focused much attention on polyploid trees because of their importance to forestry. To evaluate the impact of intraspecies genome duplication on the transcriptome, a series of Betula platyphylla autotetraploids and diploids were generated from four full-sib families. The phenotypes and transcriptomes of these autotetraploid individuals were compared with those of diploid trees. Autotetraploids were generally superior in breast-height diameter, volume, leaf, fruit and stoma and were generally inferior in height compared to diploids. Transcriptome data revealed numerous changes in gene expression attributable to autotetraploidization, which resulted in the upregulation of 7052 unigenes and the downregulation of 3658 unigenes. Pathway analysis revealed that the biosynthesis and signal transduction of indoleacetate (IAA) and ethylene were altered after genome duplication, which may have contributed to phenotypic changes. These results shed light on variations in birch autotetraploidization and help identify important genes for the genetic engineering of birch trees.

Tilia mandshurica is recognized as one of the most valuable timber, ornamental and nectariferous tree species, and its cutting propagation is very difficult. To evaluate the influence of ortet age on the rooting of T. mandshurica cuttings and the relationship between the variations of nutrients, enzyme activities, endogenous hormones and the formation of adventitious roots, a series of softwood cuttings of T. mandshurica were collected from 2-, 7-, 15- and 20-year-old healthy ortets, respectively. The rooting percentage, mean root number and total root length were investigated after 60 days of cultivation. Phenotypic and anatomical changes and the variations of organic nutrients, enzyme activities and endogenous hormones were measured during adventitious root formation. The results showed that ortet age effect existed in T. mandshurica softwood cuttings. The adventitious rooting of 2-year-old ortets was superior to that of 7-, 15- and 20-year-old ortets. No root primordium was visible in T. mandshurica softwood cuttings before cultivation, and the root primordia were induced after planting. The adventitious roots derived from vascular cambium and callus in cuttings. Soluble sugar increased during root primordium induction and decreased in adventitious root elongation. Soluble protein decreased during root primordium induction and increased in adventitious root elongation. Polyphenol oxidase (PPO) activity increasing and peroxidase (POD) and 3-indoleacetic acid oxidase (IAAO) activities decreasing were conducive to root primordium induction. High 3-indoleacetic acid (IAA) and gibberellin (GA₃) level could promote root primordium induction and low IAA and GA₃ level was beneficial to adventitious root elongation. Abscisic acid (ABA) and zeatin riboside (ZR) inhibited root primordium induction and adventitious root elongation. IAA, ABA and ZR coordinated with each other in the process of root primordium induction and adventitious root formation. IAA/ABA increasing could promote root primordium induction, and IAA/ZR increasing was beneficial to root primordium induction and adventitious root elongation. The soluble sugar content, PPO activity, IAA/ABA and IAA/ZR of softwood cuttings from 2-year-old ortets were relatively high, which may be the reason for the better adventitious rooting. The present study provides a reference to build a propagation by cuttings technology of linden trees.

A dwarf mutant (dwf1) was obtained among 15 transgenic lines, when TaLEA (Tamarix androssowii late embryogenesis abundant gene) was introduced into Populus simonii × Populus nigra by Agrobacterium tumefaciens-mediated transformation. Under the same growth conditions, dwf1 height was significantly reduced compared with the wild type and the other transgenic lines. Because only one transgenic line (dwf1) displayed the dwarf phenotype, we considered that T-DNA insertion sites may play a role in the mutant formation. The mechanisms underlying this effect were investigated using TAIL-PCR (thermal asymmetric interlaced PCR) and microarrays methods. According to the TAIL-PCR results, two flanking sequences located on chromosome IV and VIII respectively, were cloned. The results indicated the integration of two independent T-DNA copies. We searched for the potential genes near to the T-DNA insertions. The nearest gene was a putative poplar AP2 transcription factor (GI: 224073210). Expression analysis showed that AP2 was up-regulated in dwf1 compared with the wild type and the other transgenic lines. According to the microarrays results, a total of 537 genes involved in hydrolase, kinase and transcription factor activities, as well as protein and nucleotide binding, showed significant alterations in gene expression. These genes were expressed in more than 60 metabolic pathways, including starch, sucrose, galactose and glycerolipid metabolism and phenylpropanoids and flavonoid biosyntheses. Our transcriptome and T-DNA insertion sites analyses might provide some useful insights into the dwarf mutant formation.

Rhododendron dauricum is a cold-hardy shrub integrating ornamental, medicinal, and aromatic functions. Flower color is an important feature related to ornamental value for breeders and consumers. Nevertheless, the coloration mechanism of flower color in R. dauricum is still unclear. R. dauricum var. albiflorum is a white flower variety of R. dauricum. In this study, an integrative analysis of the metabolome and transcriptome was conducted between R. dauricum var. albiflorum and R. dauricum. A total of nine anthocyanins and two proanthocyanidins were differentially accumulated between R. dauricum var. albiflorum and R. dauricum. A decrease in malvidin-, delphinidin-, cyanidin-, peonidin-, and petunidin-based anthocyanins and an increase in procyanidin A2 and procyanidin B2 were responsible for the white flowers of R. dauricum var. albiflorum. Furthermore, a total of 4376 differentially expressed genes (DEGs) were identified using transcriptome sequencing. Integrated analysis of the metabolome and transcriptome showed that 21 DEGs encoding 9 enzymes (PAL, C4H, CHS, CHI, F3H, F3′5′H, DFR, ANR, and UFGT) were identified as structural genes involved in anthocyanin and proanthocyanidin biosynthesis, and 15 MYBs and 10 bHLHs were the transcriptional regulators of the anthocyanin biosynthesis pathways in R. dauricum var. albiflorum. Our results deepen the understanding of variations in azalea flower color, which is helpful for identifying important genes in the genetic engineering of azalea shrubs.

As the key transcription factors regulating auxin responsive genes expression, auxin response factors (ARFs) play critical roles in diverse aspects of plant growth and development. Betula pendula is a valuable ornamental tree, and the information on ARF gene family of B. pendula is needed for better understanding. The publication of the genome sequence of B. pendula enable to analyze the bioinformatics information and expression pattern of BpeARF gene family on the genome-wide basis. In this study, physical and chemical properties, chromosome location, phylogenetic relationship, gene structure, conserved domain, motif composition, and cis-acting element of BpeARF gene family were analyzed, and expression patterns of BpeARF genes were investigated using completely random design in different tissues and under exogenous NAA and drought treatments. A total of 17 BpeARF genes was identified from B. pendula genome, which were unevenly distributed on 13 chromosomes and encoded adequate proteins ranging from 613 to 1135 amino acids in length. Three BpeARF gene pairs were formed by segmental duplication, and the Ka/Ks values of these BpeARF gene pairs were less than 1. According to the phylogenetic relationship among B. pendula, Betula platyphylla, Populus trichocarpa, and Arabidopsis thaliana, the BpeARF genes were divided into four classes, and the intron/exon structure, conserved domain, and motif composition showed high similarity among the BpeARF genes within the same class. The cis-acting elements in the promoter regions of BpeARF genes were related to tissue development, hormone response, and stress resistance. Quantitative real-time PCR exhibited diverse expression patterns of BpeARF genes in different tissues and in response to exogenous auxin treatment and drought stress. The expressions of one, ten, seven, and three BpeARF genes were the high levels in buds, young leaves, stems, and roots, respectively. Under exogenous NAA treatment, six BpeARF genes in stems and roots were upregulated expression at all timepoints. Under drought stress, BpeARF7 and BpeARF15 were upregulated in stems and roots, and BpeARF5 and BpeARF6 were downregulated in leaves, stems, and roots. Our results provided valuable information for the classification and putative functions of BpeARF gene family, which may be helpful for selecting candidate genes and verifying gene function in the genetic engineering of birch trees in further research.

Tilia mandshurica is a multi-purpose tree species with high values for timber production, landscape ornamentation, and nectar yield. Growth traits serve as core evaluation indices for its genetic improvement, and clarifying the maternity–progeny genetic relationship is essential for efficient selective breeding. In this study, 66 maternal clones and their corresponding open-pollinated progeny families derived from the same plus trees were used as experimental materials. Six key growth traits, including tree height, basal diameter, clear bole height, branch angle, crown width, and stem straightness, were systematically measured and analyzed. Extremely significant variances in all investigated growth traits were observed among both maternal clones and progeny families. For maternal clones, the phenotypic coefficient of variation, genotypic coefficient of variation, and repeatability ranged from 37.3% to 77.2%, 1.0% to 29.1%, and 0.4286 to 0.6587, respectively. For progeny families, the phenotypic coefficient of variation and genotypic coefficient of variation varied from 35.4% to 66.9% and 0.7% to 26.7%, with heritability ranging from 0.3671 to 0.6255. Significant phenotypic and genetic correlations for growth traits were detected between maternal clones and progeny families, excluding stem straightness. Integrated principal component analysis and multi-trait comprehensive evaluation screened eight elite maternal clones (LJ03, LJ19, LJ21, LJ32, LJ40, LJ47, LJ52, LJ63) and ten elite progeny families (LJ03, LJ09, LJ21, LJ27, LJ32, LJ40, LJ46, LJ47, LJ52, LJ63). Among these materials, seven germplasms (LJ03, LJ21, LJ32, LJ40, LJ47, LJ52, LJ63) exhibited excellent performance in both clonal and family populations. The elite clones yielded genetic gains of 4.4–26.2% and realistic gains of 10.3–42.4%, while the elite families presented genetic gains of 1.5–21.2% and realistic gains of 3.1–33.8%. This study clarifies the genetic variation and maternity –progeny genetic linkage of growth traits in T. mandshurica, provides excellent elite germplasm resources for genetic improvement, and offers a theoretical and practical basis for the future construction of high-quality seed orchards of this species.