Abstract

   Codonopsis convolvulacea Kurz. var. vinciflora (Kom.) L.T. Shen is a
   member of Campanulaceae, which is used in traditional Chinese medicine.
   However, apart from a few Codonopsis species, no detailed knowledge is
   available on the metabolite composition and respective transcriptome
   signatures. We performed a combined transcriptome and metabolome
   analysis of the tuber, stem, and leaf of C. convolvulacea and found
   1,144 metabolites and 231,840 unigenes in three experimental groups.
   The analysis revealed considerable variations in the three tissues.
   Tubers were rich in amino acids and derivatives, flavonoids, and
   organic acids, whereas the stems and leaves were rich in alkaloids and
   flavonoids, respectively. Transcriptome sequencing revealed candidate
   genes being involved in flavonoid, tryptophan, and alkaloid
   biosyntheses. In particular, we indicated that the variation in the
   isoflavone content is linked to the expressions of CHI, CYP73A, C3′H,
   F3H, CYP75B1, anthocyanidin synthase, and FLS. In a similar way, the
   levels of indole, L-tyrosine, and tryptamine were also consistent with
   the expressions of TDC/DDCs in the respective tissues. In addition, the
   expression levels of ASP5, ARO8, GOT, and AOC3 indicated that
   L-tryptophan is being converted to downstream metabolites. Overall, our
   datasets present a useful resource for future research on the uses of
   this medicinal plant and put forward many research questions.

   Keywords: gene expression, medicinal plant, metabolites, biosynthesis
   pathways, tissues

1 Introduction

   Codonopsis is the largest genus in the family Campanulaceae with more
   than 40 species. These species are distributed in Asia; around 39
   species are distributed in China ([32]Hong, 2015). Members of this
   genus have long been used in traditional Tibetan medicine and are
   described in the Chinese pharmacopoeia. The most famous Codonopsis
   species include Codonopsis pilosula, C. lanceolata, C. Tangshan, C.
   clematidea, C. cordifolioidea, C. nervosa, C. thalictrifolia, C.
   xundianensis, and C. tubulosa, which have been extensively explored for
   their phytochemistry, and >100 compounds have been isolated and
   identified ([33]He et al., 2015). Phytochemical investigations have
   shown the accumulation of polyacetylenes, polysaccharides, alkaloids,
   coumarins, lignans, flavonoids, phenylpropanoids, organic acids,
   essential oils, and terpenoids. These compounds have been extracted
   from various parts such as aerial parts (stem and leaves) and
   roots/tubers; for example, phenylpropanoids were reported to occur in
   the aerial parts of C. nervosa and C. Tangshan ([34]Tsai and Lin, 2008;
   [35]Xie G et al., 2011) and in the roots of C. lanceolata ([36]Ren et
   al., 2013) and C. cordifolioidea ([37]Hu et al., 2012). Some studies
   have also focused on the chemotaxonomical identification, purification,
   and characterization of useful chemicals from this genus ([38]Wang et
   al., 1995). However, not all the species have been explored in terms of
   their phytochemistry and molecular mechanisms governing the particular
   biochemical composition. Studies involving bioactivities of the
   Codonopsis extracts have only been reported in a limited number of
   species, i.e., C. pilosula, C. lanceolata, C. clematidea, and C.
   cordifolioidea. Extracts from C. pilosula and C. lanceolata have also
   shown antitumor activity ([39]Wang et al., 1995), antidiabetic ([40]Fu
   et al., 2008), and antiaging effects ([41]Xu et al., 2006), as well as
   a protective effect against gastric mucosal damage ([42]Liang and
   Jianhua, 1989), inhibition of erythrocyte hemolysis ([43]Ng et al.,
   2004), enhancement of the nerve growth factor ([44]Liu et al., 2003),
   attenuated angiotensin II (AngII)-induced insulin-like growth factor II
   receptor promoter activity ([45]Tsai et al., 2013), and
   hepatoprotective activity ([46]Liang et al., 2007). Detailed
   exploration of Codonopsis species lags because they are found mostly in
   the wild in selected regions, which makes it difficult to collect them.

   C convolvulacea Kurz. var. vinciflora (Kom.) L.T. Shen (Flora of China;
   [47]http://www.efloras.org/florataxon.aspx?flora_id=2&taxon_id=20002289
   7) ([48]Zhang et al., 2015) is one such species that has not been
   explored in detail. It is naturally distributed in the Northwest Yunnan
   and Tibetan plateau of China (including the adjacent region of Dolpo,
   Nepal) ([49]Ghimire and Aumeeruddy-Thomas, 2009; [50]Chen et al.,
   2021). The C. convolvulacea plant has a short stem base, and few
   tumor-like scars can be seen on the stem. The leaves are alternate or
   sometimes opposite; the petioles are obvious, up to 1.6 cm long, the
   leaves are thin, membranous, the edges are toothed, and the veins are
   thin and obvious. The tubers are massive, nearly ovoid or egg-shaped.
   In the past, it was used to treat chest pain and cold and to relieve
   appetite-related issues. Furthermore, in Tibetan medicine, it is used
   for the treatment of coronary heart diseases, mountain sickness,
   strengthening of the spleen and stomach, and multiple other diseases
   ([51]Tang et al., 2017 and references therein). In Tibetan medicine, it