Overexpression of The AtWUSCHEL Gene Promotes Somatic Embryogenesis And Lateral Branch Formation In Birch (Betula Platyphylla Suk.)

Birch (Betula platyphylla Suk.) is a deciduous tree with the value of medicinal and ornamental greening. Plant somatic embryogenesis is a limiting step in birch genetic breeding. As a transcription factor, the Arabidopsis thaliana WUSCHEL (AtWUS) gene plays an important role in maintaining and regulating stem cell characteristics. It determines whether the stem cell population is differentiated. To explore the method of inducing somatic embryogenesis in birch. We overexpressed the AtWUS gene and transferred it into birch. The expression of AtWUS increased the somatic embryogenesis rate from 101.4% to 717.1%. The expression of the AtWUS gene in calli and globular embryos led to the downregulation of the BpWUS gene. The BpLEC1, BpLEC2, BpFUS3 and BpABI3 genes were upregulated. In addition, overexpression of AtWUS increased the number of lateral branches and bud meristem in birch. Similarly, the BpWUS gene was downregulated in the bud meristem. The BpLEC1, BpLEC2, BpFUS3, BpSTM and BpCUC2 genes were upregulated. This result indicated that overexpression of the AtWUS gene promoted somatic embryogenesis (SE) by increasing the expression of SE-related genes. In conclusion, this study focused on the role of the AtWUS gene in birch SE and the molecular mechanism of promoting SE.

Overexpression of BplERD15 Enhances Drought Tolerance in Betula platyphylla Suk.

In this study, we report the cloning and functional characterization of an early responsive gene, BplERD15, from Betula platyphylla Suk to dehydration. BplERD15 is located in the same branch as Morus indica Linnaeus ERD15 and Arabidopsis Heynh ERD15 in the phylogenetic tree built with ERD family protein sequences. The tissue-specific expression patterns of BplERD15 were characterized using qRT-PCR and the results showed that the transcript levels of BplERD15 in six tissues were ranked from the highest to the lowest levels as the following: mature leaves (ML) > young leaves (YL) > roots (R) > buds (B) > young stems (YS) > mature stems (MS). Multiple drought experiments were simulated by adding various osmotica including polyethylene glycol, mannitol, and NaCl to the growth media to decrease their water potentials, and the results showed that the expression of BplERD15 could be induced to 12, 9, and 10 folds, respectively, within a 48 h period. However, the expression level of BplERD15 was inhibited by the plant hormone abscisic acid in the early response and then restored to the level of control. The BplERD15 overexpression (OE) transgenic birch lines were developed and they did not exhibit any phenotypic anomalies and growth deficiency under normal condition. Under drought condition, BplERD15-OE1, 3, and 4 all displayed some drought tolerant characteristics and survived from the drought while the wild type (WT) plants withered and then died. Analysis showed that all BplERD15-OE lines had significant lower electrolyte leakage levels as compared to WT. Our study suggests that BplERD15 is a drought-responsive gene that can reduce mortality under stress condition.

A model form for stem taper and volume estimates of Asian white birch (Betula platyphylla): a major commercial tree species of Northeast China

Stem taper functions are valuable tools for the study of stem profile and predict volume estimates. Such functions have long been analyzed for different birch species in the world. However, Asian white birch (Betula platyphylla Suk.) has not yet been investigated as an individual species in China or abroad. This study presents stem taper and volume equations for B. platyphylla in Northeast China. Eight commonly used taper functions were fit to the data of 615 destructively sampled trees from two regions of Northeast China. A second-order continuous autoregressive error structure was incorporated to address the autocorrelation in the data and to achieve the valid parameter estimation. The condition number was used to detect the multicollinearity in the models. The taper functions were compared in terms of overall evaluation statistics and by examining the box plots of diameter and volume residuals against relative heights and diameter classes. The equations of A. Kozak (2004, For. Chron. 80(4): 507–515; model 2), Z. Fang et al. (2000, For. Sci. 46(1): 1–12), and H. Bi (2000, For. Sci. 46(3): 397–409) were the leading models for diameter and volume estimates. Overall, the equation of Z. Fang et al. (2000, For. Sci. 46(1): 1–12) exhibited the best results for estimating diameter and total and merchantable volumes in terms of statistical performance and lower multicollinearity.