Overexpression of the AtWUSCHEL gene promotes somatic embryogenesis and lateral branch formation in birch (Betula platyphylla Suk.)

Abstract

Birch (Betula platyphylla Suk.) is a deciduous tree with medicinal and ornamental value. During the process of genetic transformation, somatic embryos do not easily develop into transgenic plants, which is a limitation in genetic breeding. The Arabidopsis thaliana WUSCHEL (AtWUS) gene, which is a transcription factor, plays an important role in maintaining and regulating stem cell characteristics, which determines whether the stem cell population is differentiated. To explore methods for inducing somatic embryogenesis (SE) in birch, we overexpressed the AtWUS gene and transferred it to birch. The expression of AtWUS increased the SE rate from 101.4 to 717.1%. The expression of the AtWUS gene led to the downregulation of BpWUS gene expression in both calli and globular embryos as well as bud meristems. The expression of a few genes, i.e., BpLEC1 (LEAFY COTYLEDON 1), BpLEC2 (LEAFY COTYLEDON 2) and BpFUS3 (FUSCA 3), was upregulated during both embryogenesis and bud meristem development. However, BpABI3 (ABSCISIC ACID INSENSITIVE 3) gene expression was upregulated only in calli embryos, while BpSTM (SHOOT MERISTEMLESS) and BpCUC2 (CUP-SHAPED COTYLEDON 2) gene expression was upregulated only in bud meristems. This result indicated that overexpression of the AtWUS gene promoted 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 by which SE was promoted. This work indicates that overexpression of the WUSCHEL gene from Arabidopsis thaliana in birch can promote somatic embryogenesis and increase the development of lateral branches and buds.