Functional analysis of StDWF4 gene in response to salt stress in potato

The DWARF4 (DWF4) gene encodes a C-22 hydroxylase which is pivotal for brassinosteroids (BRs) biosynthesis. In this research, aimed to understand the molecular mechanism of DWF4 on regulation of potatoes tolerance to salt stress, DWF4 was cloned from potato, named as StDWF4. Its 1476 bp open reading frame encodes a protein of 491 amino acids. The StDWF4-overexpressing (OE) and interference-expressing (RNAi) transgenic potato plants were acquired using Agrobacterium-mediated transformation, respectively. Tissue specific analysis using Quantitative real-time polymerase chain reaction (qRT-PCR) demonstrated that the StDWF4 gene expressed in the leaves, stems and roots of the transgenic and un-transgenic (NT) plants, with specially increased (StDWF4-OE)/reduced (StDWF4-RNAi) expression in the roots. The content of malondialdehyde (MDA) in StDWF4-OE potato plants was lower than that of NT, and proline content was higher than that of NT. MDA and proline content in StDWF4-OE and NT under salt-stress was significantly higher than that of the control and was increased at different sampling times. The content of soluble protein, soluble sugar and the activities of superoxide dismutase (SOD), peroxidase (POD) and ascorbate peroxidase (APX) was higher in the StDWF4-OE plantlets at varied salt treatment time than in the NT potatoes. Reduction of H2O2 content in the StDWF4-OE plants was observed. All above plant physiology indicators in the StDWF4-RNAi potatoes showed opposite variation trends. The results proved that the overexpressing of StDWF4 in potato plantlets can enhance the salt resistance by alleviating the negative effects of salt-stress. However, its interference expression in potato plants depresses the salt resistance. The results lay the groundwork for intensive study of BRs regulation in potato growth and development, and will help us to reveal the molecular mechanisms of how the BRs signaling regulate potato salt tolerance.