Overexpression of the Lipid Transfer Protein Gene SpLTP1 from Desert Pioneer Plant Stipagrostis pennata Enhances the Drought Tolerance in Arabidopsis

Lipid transfer proteins (LTPs) play crucial regulatory roles in plant growth, development, and abiotic stress responses. Stipagrostis pennata is a species of grass widely distributed in arid and semi-arid regions, particularly adapted to desert and steppe environments. Under extreme drought conditions, it exhibits a variety of physiological and morphological adaptation mechanisms, making it an important species for studying plant drought tolerance. Recently, LTPs have been found to exhibit upregulated expression under drought stress in plants such as wheat and tobacco, enhancing their drought tolerance. However, the functional role of LTPs in S. pennata remains unexplored. In this study, the SpLTP1 gene was isolated from S. pennata via molecular cloning, encoding a 116-amino acid protein. Phylogenetic analysis revealed that this protein contains a highly conserved nsLTP1 (cd01960) domain and has high sequence similarity with LTPs of Setaria viridis, Setaria italica, Musa acuminata and Phragmites australis. qRT-PCR revealed that SpLTP1 was highly expressed and dynamically regulated under drought, suggesting its potential role in root rhizosheath formation and drought tolerance. To investigate SpLTP1 function, SpLTP1-overexpressing (SpLTP1-OE) and complementation (SpLTP1-atltp) Arabidopsis lines were generated using the floral dip method, in comparison with the existing wild-type (WT) and the LTP-deficient mutant (atltp). Drought stress phenotyping and physiological assays indicated that SpLTP1 likely enhances drought tolerance by elevating antioxidant enzyme activities and osmolyte accumulation. Comparative transcriptome analysis of SpLTP1-OE and WT plants further suggested that SpLTP1 modulates critical pathways, including phenylpropanoid biosynthesis, zeatin biosynthesis, and plant hormone signal transduction, thereby influencing plant growth and stress adaptation. These findings not only provide novel insights into the molecular mechanisms by which SpLTP1 regulates rhizosheath development in S. pennata but also establish a foundation for deciphering its role in extreme drought adaptation.