Transcriptomic Profiling Reveals Key Genes of Halophyte Apocyni Veneti Folium (Apocynum venetum L.) and Regulatory Mechanism of Salt Tolerance

Apocyni Veneti Folium (AVF) is a salt-tolerant medicinal halophyte and soil salinity is a main stress affecting its quality. Molecular bases involved in quality evaluation and ecological adaptations to abiotic constraints can be explored using omics tools. In the study, AVF was treated with four levels of salt stress (control, 100, 200 and 300 mM NaCl, respectively) and subjected to de novo-based RNA-sequencing. We constructed GO and KEGG analysis on the obtained DEGs. After molecular phylogenetic analysis, we isolated and characterized one representative and up-regulated candidate gene AvUGT (Tr_AVENL_25169) encoding UDP-glucosyltransferase under salt stress. Results showed that the obtained clean reads were assembled into a total of 54,276 high-quality unigenes. Notably, specific genes related to flavonoid glucoside biosynthesis and salt-tolerant regulation, such as genes encoding transcription factors, transporters, glucosyltransferase, heat shock protein and plant hormone signal transduction-related protein, preferentially up-regulated by low level of salt. Combined with previous metabonomic analysis, the results revealed key genes that contribute to elucidate the reduced salt toxicity in AVF. Furthermore, the transcript profiles of UGT genes were consistent with the accumulation of flavonoid glycosides in AVF; the candidate gene AvUGT probably plays a critical role in biosynthesis of flavonoid glucosides in response to salt environment. These results provided a basis for future research on the regulatory mechanism of salt stress of medicinal halophyte AVF.