Abstract
The aim of this study was to determine whether transgenic birch (Betula platyphylla) ectopic overexpressing a late embryogenesis abundant (LEA) gene and a basic leucine zipper (bZIP) gene from the salt-tolerant genus Tamarix (salt cedar) show increased tolerance to salt (NaCl) stress. Co-transfer of TaLEA and ThbZIP in birch under the control of two independent CaMV 35S promoters significantly enhanced salt stress. PCR and northern blot analyses indicated that the two genes were ectopically overexpressed in several dual-gene transgenic birch lines. We compared the effects of salt stress among three transgenic birch lines (L-4, L-5, and L-8) and wild type (WT). In all lines, the net photosynthesis values were higher before salt stress treatment than afterwards. After the salt stress treatment, the transgenic lines L-4 and L-8 showed higher values for photosynthetic traits, chlorophyll fluorescence, peroxidase and superoxide dismutase activities, and lower malondialdehyde and Na+ contents, compared with those in WT and L-5. These different responses to salt stress suggested that the transcriptional level of the TaLEA and ThbZIP genes differed among the transgenic lines, resulting in a variety of genetic and phenotypic effects. The results of this research can provide a theoretical basis for the genetic engineering of salt-tolerant trees.
Highlights
Birch (Betula Platyphylla) is one of the most extensively distributed broadleaf species in the northern and southwestern forested areas of China [1]
The TaLEA gene (GenBank accession NO.: DQ663481) was isolated from T. androssowii, which belongs to late embryogenesis abundant 3 superfamily protein
A northern blot analysis confirmed that three of the transgenic lines (L-4, L-5 and L-8) had distinct bands corresponding to TaLEA and ThbZIP genes, while the wild type did not, confirming that the TaLEA and ThbZIP genes were successfully transcribed in mRNA level (Fig 3)
Summary
Birch (Betula Platyphylla) is one of the most extensively distributed broadleaf species in the northern and southwestern forested areas of China [1]. Soil salinity, which is a major abiotic stress that reduces plant productivity, affects large areas around the world [12]. The osmotic stress and ion toxicity associated with saline soils result in low plant yields and negatively affect the growth of agricultural and forest crops [14]. To ensure both their own survival and that of their offspring, plants have developed a range of strategies, including gene expression regulation, to cope with adverse conditions through various physiological adaptations [15]
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