A Non-specific Setaria italica Lipid Transfer Protein Gene Plays a Critical Role under Abiotic Stress

Abstract

Lipid transfer proteins (LTPs) are a class of cysteine-rich soluble proteins having small molecular weights. LTPs participate in flower and seed development, cuticular wax deposition, also play important roles in pathogen and abiotic stress responses. A non-specific LTP gene (<i>SiLTP</i>) was isolated from a foxtail millet (<i>Setaria italica</i>) suppression subtractive hybridization library enriched for differentially expressed genes after abiotic stress treatments. A semi-quantitative reverse transcriptase PCR analysis showed that <i>SiLTP</i> was expressed in all foxtail millet tissues. Additionally, the <i>SiLTP</i> promoter drove GUS expression in root tips, stems, leaves, flowers, and siliques of transgenic <i>Arabidopsis</i>. Quantitative real-time PCR indicated that the <i>SiLTP</i> expression was induced by NaCl, polyethylene glycol, and abscisic acid (ABA). SiLTP was localized in the cytoplasm of tobacco leaf epidermal cells and maize protoplasts. The ectopic expression of <i>SiLTP</i> in tobacco resulted in higher levels of salt and drought tolerance than in the wild type (WT). To further assess the function of SiLTP, <i>SiLTP</i> overexpression (OE) and RNA interference (RNAi)-based transgenic foxtail millet were obtained. <i>SiLTP</i>-OE lines performed better under salt and drought stresses compared with WT plants. In contrast, the RNAi lines were much more sensitive to salt and drought compared than WT. Electrophoretic mobility shift assays and yeast one-hybrids indicated that the transcription factor ABA-responsive DRE-binding protein (SiARDP) could bind to the dehydration-responsive element of <i>SiLTP</i> promoter <i>in vitro</i> and <i>in vivo</i>, respectively. Moreover, the <i>SiLTP</i> expression levels were higher in <i>SiARDP</i>-OE plants compared than the WT. These results confirmed that <i>SiLTP</i> plays important roles in improving salt and drought stress tolerance of foxtail millet, and may partly be upregulated by SiARDP. <i>SiLTP</i> may provide an effective genetic resource for molecular breeding in crops to enhance salt and drought tolerance levels.