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 (SiLTP) was isolated from a foxtail millet (Setaria italica) suppression subtractive hybridization library enriched for differentially expressed genes after abiotic stress treatments. A semi-quantitative reverse transcriptase PCR analysis showed that SiLTP was expressed in all foxtail millet tissues. Additionally, the SiLTP promoter drove GUS expression in root tips, stems, leaves, flowers, and siliques of transgenic Arabidopsis. Quantitative real-time PCR indicated that the SiLTP 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 SiLTP in tobacco resulted in higher levels of salt and drought tolerance than in the wild type (WT). To further assess the function of SiLTP, SiLTP overexpression (OE) and RNA interference (RNAi)-based transgenic foxtail millet were obtained. SiLTP-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 SiLTP promoter in vitro and in vivo, respectively. Moreover, the SiLTP expression levels were higher in SiARDP-OE plants compared than the WT. These results confirmed that SiLTP plays important roles in improving salt and drought stress tolerance of foxtail millet, and may partly be upregulated by SiARDP. SiLTP may provide an effective genetic resource for molecular breeding in crops to enhance salt and drought tolerance levels.
Highlights
IntroductionEnvironmental problems are becoming more severe. Among the major factors, drought, salinity, and cold stresses adversely affect the growth and yield of plants (Mahajan and Tuteja, 2005)
Between nsLTP2 and specific LTP gene (SiLTP), 64.7% of positional sequence identity and 53% similarity reflected the high degree of matching between the nsLTP2 model and SiLTP
Most found that Lipid transfer proteins (LTPs) II-type genes are associated with seed development (GarccA-Garrido et al, 1998; Monnet et al, 2001; Castro et al, 2003)
Summary
Environmental problems are becoming more severe. Among the major factors, drought, salinity, and cold stresses adversely affect the growth and yield of plants (Mahajan and Tuteja, 2005). In response to abiotic stresses, plants have developed diverse signaling pathways. Various genes, including those of enzymes, transcription factors (TFs), and functional proteins that participate in mitigating the effects of stress, adjust to the cellular milieu and increase plant tolerance. Foxtail millet (Setaria italica) is an important millet crop worldwide and has been cultivated in China for more than 7,000 years. In India, China, and Japan, foxtail millet is normally cultivated in the salinity- and drought-prone regions. Extensive adaptability, rich genetic diversity, and a small diploid genome about 490 Mb (Doust et al, 2009), foxtail millet provides a rich resource of stress resistance genes for study and application. Considerable progress has been made on the whole-genome sequencing of foxtail millet (Bennetzen et al, 2012; Zhang et al, 2012; Jia et al, 2013), foxtail millet were recommended as an excellent C4 crop model (Doust et al, 2009; Bennetzen et al, 2012; Kumar et al, 2013; Muthamilarasan and Prasad, 2015)
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