Screening and functional identification of salt tolerance HMG genes in Betula platyphylla

High mobility group (HMG) proteins play an important role in plant responses to abiotic stresses. However, to date, few studies have focused on the functional characterization of HMG genes in woody plants. In this study, 11 BpHMG genes named BpHMG1-BpHMG11 were cloned and characterized from Betula platyphylla. The expression patterns of BpHMG genes under two types of abiotic stress (osmotic and salt stress) and ABA (abscisic acid) treatments were detected by qRT-PCR. The results showed that the expression of 11 BpHMG genes in birch roots, stems and leaves changed in at least one stress treatment time point under all three treatments, suggesting that 11 BpHMG genes could respond to salt, osmotic stress and ABA treatment. In particular, the expression of BpHMG6 in birch stems was significantly upregulated at all studied time points under NaCl stress. The highest level was increased up to 118-fold compared with the control, indicating that this gene may be involved in salt stress responses. To further study the salt tolerance function of BpHMG6, the overexpression vector pROKIIBpHMG6 and silencing expression vector pFGC-BpHMG6 were constructed and transiently transformed into birch. The empty vector pROKII was also transformed as a control. POD activity, H2O2 and MDA levels, relative electrolyte and NBT, DAB and Evans blue staining were analysed and compared between transgenic and control plants under salt stress. The results indicated that the overexpression of BpHMG6 in birch not only increased the activity of protective enzymes under salt stress but also enhanced the ROS scavenging capacity to reduce cell damage and death caused by salt stress. Conversely, the silenced transiently transformed plants displayed the opposite physiological changes. Therefore, BpHMG6 potentially plays a role in salt stress tolerance in transgenic birch plants.

Automated summary

In this study, 11 BpHMG genes were cloned and characterized from Betula platyphylla, showing response to salt, osmotic stress and ABA treatment. Particularly, BpHMG6 exhibited significant upregulation in birch stems under salt stress. Overexpression of BpHMG6 in birch enhanced salt tolerance by increasing protective enzyme activity and ROS scavenging capacity, while silenced plants showed opposite responses. Therefore, BpHMG6 potentially plays a role in salt stress tolerance in transgenic birch plants.