Transcriptomic Analysis Reveals the Regulatory Mechanism of Cold Tolerance in Saussurea involucrata: The Gene Expression and Function Characterization of Dehydrins

Abstract

Saussurea involucrata, a rare and endangered medicinal plant of the Asteraceae family, is primarily distributed in high-altitude rocky slopes and meadows at elevations of 2400–4100 m. In nature, this herb endures various abiotic stresses, including intense cold and ultraviolet radiation. In our study, transcriptomic profiles revealed that most of the differentially expressed genes (DEGs) enriched in stress response pathways, such as “response to water”, “response to abscisic acid”, “cold acclimation”, and “response to water deprivation”, were significantly upregulated after low-temperature treatment. In contrast, the majority of genes with lower expression were related to “photosynthesis”, “protein–chromophore linkage”, and “chloroplast thylakoid membrane”. Among them, Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) database analysis revealed that approximately 20 DEGs were identified and annotated as dehydrin genes (DHNs). Quantitative PCR (qPCR) validation also confirmed that these DHNs were upregulated under cold stress. Moreover, SiDHN3, a new dehydrin gene, was cloned by Rapid Amplification of cDNA Ends (RACE). SiDHN3’s heterologous expression in E. coli showed enhanced salt, osmotic, freeze–thaw, and cold stress tolerance. A functional analysis of SiDHN3’s truncated derivatives revealed that the K-segment was critical for its protective function under freeze–thaw and cold stresses. Collectively, our study demonstrated the potential role of various DHNs as a functional protein, enhancing tolerance to cold stress in the high-altitude adaptation of plants.