Comparative Transcriptome Analysis Identifies Putative Genes Involved in the Biosynthesis of Xanthanolides in Xanthium strumarium L.

Abstract

Xanthium strumarium L. is a traditional Chinese herb belonging to the Asteraceae family. The major bioactive components of this plant are sesquiterpene lactones (STLs), which include the xanthanolides. To date, the biogenesis of xanthanolides, especially their downstream pathway, remains largely unknown. In X. strumarium, xanthanolides primarily accumulate in its glandular trichomes. To identify putative gene candidates involved in the biosynthesis of xanthanolides, three X. strumarium transcriptomes, which were derived from the young leaves of two different cultivars and the purified glandular trichomes from one of the cultivars, were constructed in this study. In total, 157 million clean reads were generated and assembled into 91,861 unigenes, of which 59,858 unigenes were successfully annotated. All the genes coding for known enzymes in the upstream pathway to the biosynthesis of xanthanolides were present in the X. strumarium transcriptomes. From a comparative analysis of the X. strumarium transcriptomes, this study identified a number of gene candidates that are putatively involved in the downstream pathway to the synthesis of xanthanolides, such as four unigenes encoding CYP71 P450s, 50 unigenes for dehydrogenases, and 27 genes for acetyltransferases. The possible functions of these four CYP71 candidates are extensively discussed. In addition, 116 transcription factors that are highly expressed in X. strumarium glandular trichomes were also identified. Their possible regulatory roles in the biosynthesis of STLs are discussed. The global transcriptomic data for X. strumarium should provide a valuable resource for further research into the biosynthesis of xanthanolides.

Transcriptome Assembly and Systematic Identification of Novel Cytochrome P450s in Taxus chinensis

“…Last year, 70 highly expressed CYP450s in the Xanthium strumarium trichomes were studied using an extensive analysis of transcriptomes. Among them, four CYP71 members (CYP71AV14, CYP71BL7, CYP71DD1, and CYP71AX30) were found to be the candidates involved in sesquiterpene lactone biosynthesis (Li et al, 2016 ). Transcriptome identification of genes for Taxol biosynthesis has been studied, however, no study has demonstrated interest in the CYP450 genes of Taxus (Wu et al, 2011 ; Sun et al, 2013 ).…”

Characterization of CYP71AX36 from Sunflower (Helianthus annuus L., Asteraceae)

“…5a, Supplemental Data 2). One of the closest homologs to CYP71AX36 is CYP71AX30 from Xanthium strumarium , which was recently considered as a candidate for the involvement in STL metabolism based on gene expression studies 13 . A search for sub-genomic localization revealed that all enzymes thus far characterized in the STL metabolism of Helianthus annuus , are scattered across the genome 3 (Supplementary Fig.…”

Identification of a Unique Germacrene A Oxidase from Xanthium strumarium

“…In addition, it has shown inhibitory activities against several tumor cells, including breast cancer [6], colorectal cancer [7], and glioma cells [8]. In spite of many studies concerning the medical activities of xanthatin, the genes and enzymes involved in its biosynthesis are largely unknown [9].…”

“…Nothing is known about the later stages of xanthatin biosynthesis after the formation of germacrene A. However, judging from the structure of xanthatin, the steps from germacrene A to xanthatin presumably include multiple oxidations, and enzymes of cytochrome P450s and alcohol and aldehyde dehydrogenases may be involved in these oxidation steps [9]. The specific accumulation of xanthatin in X. strumarium trichomes indicates that the trichome may be site for transcribing the xanthatin biosynthetic genes [15].…”