Abstract
Pseudostellaria heterophylla (Miq.) Pax is a mild tonic herb widely cultivated in the Southern part of China. The tuberous roots of P. heterophylla accumulate high levels of secondary metabolism products of medicinal value such as saponins, flavonoids, and isoquinoline alkaloids. Despite numerous studies on the pharmacological importance and purification of these compounds in P. heterophylla, their biosynthesis is not well understood. In the present study, we used Illumina HiSeq 4000 sequencing platform to sequence the RNA from flowers, leaves, stem, root cortex and xylem tissues of P. heterophylla. We obtained 616,413,316 clean reads that we assembled into 127, 334 unique sequences with an N50 length of 951 bp. Among these unigenes, 53,184 unigenes (41.76%) were annotated in a public database and 39, 795 unigenes were assigned to 356 KEGG pathways; 23,714 unigenes (8.82%) had high homology with the genes from Beta vulgaris. We discovered 32, 095 DEGs in different tissues and performed GO and KEGG enrichment analysis. The most enriched KEGG pathway of secondary metabolism showed up-regulated expression in tuberous roots as compared with the ground parts of P. heterophylla. Moreover, we identified 72 candidate genes involved in triterpenoids saponins biosynthesis in P. heterophylla. The expression profiles of 11 candidate unigenes were analyzed by quantitative real-time PCR (RT-qPCR). Our study established a global transcriptome database of P. heterophylla for gene identification and regulation. We also identified the candidate unigenes involved in triterpenoids saponins biosynthesis. Our results provide an invaluable resource for the secondary metabolites and physiological processes in different tissues of P. heterophylla.
Highlights
Pseudostellaria heterophylla (Miq.) Pax, known as Hai Er Shen (HES) and false starwort belongs to the Caryophyllaceae family
After removal of ambiguous reads and low-quality reads (Q20 < 20), 127,334 unique sequences were obtained from the cDNA library constructed from P. heterophylla flowers, stem, leaves, and tuberous roots of (Table 1)
The length of unigenes ranged from 201 to 82, 236 bp, with an N50 length of 951 bp. 48, 860 coding sequences were obtained from all P. heterophylla unigenes sequences, and 30, 396 CDSs (62.21%) were longer than 1000 bp
Summary
Pseudostellaria heterophylla (Miq.) Pax, known as Hai Er Shen (HES) and false starwort belongs to the Caryophyllaceae family. Some of candidate genes involved in triterpene saponin biosynthesis were isolated from P. quinquefolium [7], P. ginseng [8], and P. notoginseng [9], but none were identified from P. heterophylla. Tuberous roots or stem, are the primary medicinal plant organs of TCM plants such as P. heterophylla [10], Fallopia multiflora [11], Panax notoginseng [12], Salvia miltiorrhiza [13]. Chemical technology has helped identify the secondary metabolites including flavonoids, an isoquinoline alkaloid, terpenoids, and phenylpropanoid in these plants [3]; there have been no molecular studies on secondary metabolism pathways involved in their biosynthesis and degradation. Heterophylla was constructed to identify the differentially expressed genes (DEGs) in different tissues and putative genes encoding the enzymes involved in the biosynthesis of triterpene saponins
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