Genome sequencing-based transcriptomic analysis reveals novel genes in Peucedanum praeruptorum.

Background: Peucedanum praeruptorum Dunn, a traditional Chinese herbal medicine, contains coumarin and volatile oil components that have clinical application value. However, early bolting often occurs in the medicinal materials of Apiaceae plants. The rhizomes of the medicinal parts are gradually lignified after bolting, resulting in a sharp decrease in the content of coumarins. At present, the link between coumarin biosynthesis and early bolting in P. praeruptorum has not been elucidated.

Results: Combining the genome sequencing and the previous transcriptome sequencing results, we reanalyzed the differential transcripts of P. praeruptorum before and after bolting. A total of 62,088 new transcripts were identified, of which 31,500 were unknown transcripts. Functional classification and annotation showed that many genes were involved in the regulation of transcription, defense response, and carbohydrate metabolic processes. The main domains are the pentatricopeptide repeat, protein kinase, RNA recognition motif, leucine-rich repeat, and ankyrin repeat domains, indicating their pivotal roles in protein modification and signal transduction. Gene structure analysis showed that skipped exon (SE) was the most dominant alternative splicing, followed by the alternative 3' splice site (A3SS) and the alternative 5' splice site (A5SS). Functional enrichment of differentially expressed genes showed that these differentially expressed genes mainly include transmembrane transporters, channel proteins, DNA-binding proteins, polysaccharide-binding proteins, etc. In addition, genes involved in peroxisome, hexose phosphate pathway, phosphatidylinositol signaling system, and inositol phosphate metabolism pathway were greatly enriched. A protein-protein interaction network analysis discoverd 1,457 pairs of proteins that interact with each other. The expression levels of six UbiA genes, three UGT genes, and four OMT genes were higher during the bolting stage. This observation suggests their potential involvement in the catalytic processes of prenylation, glycosylation, and methylation of coumarins, respectively. A total of 100 peroxidase (PRX) genes were identified being involved in lignin polymerization, but only nine PRX genes were highly expressed at the bolting stage. It is worth noting that 73 autophagy-related genes (ATGs) were first identified from the KEGG pathway-enriched genes. Some ATGs, such as BHQH00009837, BHQH00013830, and novel8944, had higher expression levels after bolting.

Conclusions: Comparative transcriptome analysis and large-scale genome screening provide guidance and new opinions for the identification of bolting-related genes in P. praeruptorum.