To evaluate differences among poplar clones of various ploidies, 12 hybrid poplar clones (P. simonii × P. nigra) × (P. nigra × P. simonii) with different ploidies were used to study phenotypic variation in growth traits and photosynthetic characteristics. Analysis of variance showed remarkable differences for each of the investigated traits among these clones (P < 0.01). Coefficients of phenotypic variation (PCV) ranged from 2.38% to 56.71%, and repeatability ranged from 0.656 to 0.987. The Pn (photosynthetic rate) photosynthetic photon flux density (PPFD) curves of the 12 clones were S-shaped, but the Pn-ambient CO2 (Ca) curves were shaped like an inverted “V”. The stomatal conductance (Gs)-PPFD and transpiration rate (Tr)-PPFD curves had an upward tendency; however, with increasing PFFD, the intercellular CO2 concentration (Ci)-PPFD curves had a downward tendency in all of the clones. The Pn-PPFD and Pn-Ca curves followed the pattern of a quadratic equation. The average light saturation point and light compensation point of the triploid clones were the highest and lowest, respectively, among the three types of clones. For Pn-Ca curves, diploid clones had a higher average CO2 saturation point and average CO2 compensation point compared with triploid and tetraploid clones. Correlation analyses indicated that all investigated traits were strongly correlated with each other. In future studies, molecular methods should be used to analyze poplar clones of different ploidies to improve our understanding of the growth and development mechanisms of polyploidy.

Approximately, 20% of arable land worldwide, as well as nearly half of irrigated land, is subjected to salt stress. Osmotic stress and ion toxicity due to saline soils cause low crop yields. In this study, we introduced 18 families of salt-tolerant birch (Betula pendula Roth., Betula kirghisorum Sav.-Ryczg., and Betula pubescens Ehrh) into five high-salinity locations in northeastern China and evaluated their survival abilities. We also analyzed variation and stability of genotypeenvironment interactions of the different families under an additive main effect and multiplicative interaction model. Survival rate analysis indicated that the introduced families were well adapted to the high-salinity environments, whereas native families died. Variation analysis revealed significant differences between location × family interaction mean values for height and basic stem diameter (BSD), suggesting that most genotypes responded differently to different sites. The heritability of tree height and BSD at different sites varied from 0.416 to 0.940, with the coefficient of phenotypic variation ranging from 9.88% to 35.53%. Stability analysis indicated that some families had high tree heights but were sensitive to environmental conditions, whereas others were resistant but had average tree heights. These results suggest that families should be bred in various habitats to assess growth under favorable and unfavorable environments.

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The CUP-SHAPED COTYLEDON 2 (CUC2) gene, which is negatively regulated by microRNA164 (miR164), has been specifically linked to the regulation of leaf margin serration and the maintenance of phyllotaxy in model plants. However, few studies have investigated these effects in woody plants. In this study, we integrated genomic, transcriptomic, and physiology approaches to explore the function of BpCUC2 gene in Betula pendula growth and development. Our results showed that Betula pendula plants overexpressing BpCUC2, which is targeted by BpmiR164, exhibit shortened internodes and abnormal leaf shapes. Subsequent analysis indicated that the short internodes of BpCUC2 overexpressed transgenic lines and were due to decreased epidermal cell size. Moreover, transcriptome analysis, yeast one-hybrid assays, and ChIP-PCR suggested that BpCUC2 directly binds to the LTRECOREATCOR15 (CCGAC), CAREOSREP1 (CAACTC), and BIHD1OS (TGTCA) motifs of a series of IAA-related and cyclin-related genes to regulate expression. These results may be useful to our understanding of the functional role and genetic regulation of BpCUC2.

To investigate the molecular mechanism of the mutation of a multiple-branches birch mutant (br), we explored genes that were genome-wide differentially expressed in the main and lateral branches’ apical buds of br. The plant architecture not only has effects on the process of plant growth and development, but also affects the agronomic characters. In woody plants, branches determine the application value of timber. Therefore, analyzing genes that were differentially expressed in br apical buds will bring new insights to understand the molecular basis of plant architecture alteration. Wild type (WT) birch, Cinnamoyl-CoA reductase 1 (CCR1)-overexpressed transgenic birch (OE2) and the mutant br were used as materials to observe phenotype differences between br and the control lines (WT and OE2). The transcriptome sequencing of the main and lateral branches’ apical buds of br and controls were further performed to explore genes that were genome-wide differentially expressed in br. Compared to the control lines, br exhibited a multiple-branches and dwarf phenotype. In addition, biomass, rooting number, leaf area, internal diameter, and external diameter of stomata, and the size of terminal buds of br were less than that of WT and OE2. Transcriptome analysis results indicated that gene expression profiles of br were different from the control lines. The genes that were differentially expressed in br apical buds were involved in multiple pathways, including organogenesis, fertility regulation, cell division and differentiation, plant hormone biosynthesis, and signal transduction. The multiple-branches, dwarf, and small leaves and buds of br might be due to the differentially expressed genes (DEGs) involved in organogenesis, cell division and differentiation, plant hormone biosynthesis and signal transduction.