Background: Cardamine violifolia, native to China, is one of the selenium (Se) hyperaccumulators. The mechanism of Se metabolism and tolerance remains unclear, and only limited genetic information is currently available. Therefore, we combined a PacBio single-molecule real-time (SMRT) transcriptome library and the Illumina RNA-seq data of sodium selenate (Na₂SeO₄)-treated C. violifolia to further reveal the molecular mechanism of Se metabolism. Results: The concentrations of the total, inorganic, and organic Se in C. violifolia seedlings significantly increased as the Na₂SeO₄ treatment concentration increased. From SMRT full-length transcriptome of C. violifolia, we obtained 26,745 annotated nonredundant transcripts, 14,269 simple sequence repeats, 283 alternative splices, and 3407 transcription factors. Fifty-one genes from 134 transcripts were identified to be involved in Se metabolism, including transporter, assimilatory enzyme, and several specific genes. Analysis of Illumina RNA-Seq data showed that a total of 948 differentially expressed genes (DEGs) were filtered from the four groups with Na₂SeO₄ treatment, among which 11 DEGs were related to Se metabolism. The enrichment analysis of KEGG pathways of all the DEGs showed that they were significantly enriched in five pathways, such as hormone signal transduction and plant-pathogen interaction pathways. Four genes related to Se metabolism, adenosine triphosphate sulfurase 1, adenosine 5′-phosphosulfate reductase 3, cysteine (Cys) desulfurase 1, and serine acetyltransferase 2, were regulated by lncRNAs. Twenty potential hub genes (e.g., sulfate transporter 1;1, Cys synthase, methionine gamma-lyase, and Se-binding protein 1) were screened and identified to play important roles in Se accumulation and tolerance in C. violifolia as concluded by weighted gene correlation network analysis. Based on combinative analysis of expression profiling and annotation of genes as well as Se speciation and concentration in C. violifolia under the treatments with different Na₂SeO₄ concentrations, a putative Se metabolism and assimilation pathway in C. violifolia was proposed. Conclusion: Our data provide abundant information on putative gene transcriptions and pathway involved in Se metabolism of C. violifolia. The findings present a genetic resource and provide novel insights into the mechanism of Se hyperaccumulation in C. violifolia.

Fermentation of mulberry juice not only improves its shelf life, but also effectively enhances their flavor and nutritional quality. This study elucidated the phytochemical and flavor characteristics of mulberry juice fermented with Lactiplantibacillus plantarum BXM2, originally isolated from naturally fermented fruit beverage, through widely targeted metabolomics. The fermentation produced the unique flavor of fermented juice and decreased the pH from 4.15 to 3.19. The metabolomic analysis detected 907 non-volatile metabolites, from which 359 significantly different non-volatile metabolites (up 238, down 121) were screened out. Among 731 identified volatile metabolites, 26 flavor substances were the major contributors to the flavor differences between fermented and unfermented mulberry juices. It is hypothesized that lipid metabolism and amino acid catabolism are crucial pathways for the flavor enhancement of mulberry juice fermented with L. plantarum BXM2. Meanwhile, significant increases of the contents of a variety of bioactive substances, such as indole-3-lactic acid, octadeca-9,12,15-trienoic acid, di-/tri-peptides, etc., conferred additional health potential to BXM2-fermented mulberry juice.