Comparative transcriptome analysis to identify genes involved in terpenoid biosynthesis in Agriophyllum squarrosum , a folk medicinal herb native to Asian temperature deserts

Agriophyllum squarrosum is a folk Mongolian medicine with pleiotropic pharmacological and ecological economic importance endemic to Asian temperature deserts. Terpenoids play critical roles in biotic and abiotic stresses due to their anti-oxidative activities. Based on non-targeted metabolomic analysis, we detected eight terpenoids enriched in the above-ground tissues of A. squarrosum , however, the molecular mechanism underlying terpenoids biosynthesis in this desert medicinal plant is rarely understood. Here, a comparative transcriptome analysis of different tissues in A. squarrosum was conducted to identify 84 unigenes encoding key enzymes in the upstream backbone biosynthesis and 53 unigenes encoding the downstream enzymes for terpenoid diversification. Most of the upstream genes exhibited significant high expression levels in leaf, and some of which were validated by qRT-PCR. Phylogenetic analysis showed that two downstream gene families OSCs (oxidosqualene cyclases) and TPSs (mainly in terpene synthases -g subfamily) had undergone notable gene expansions in A. squarrosum comparing with the other Amaranthaceae plant species and Arabidopsis. Nevertheless, most members from these two gene families showed the tissue-specific expression in A. squarrosum , which supported the diversification and tissue-specific enrichment of terpenoids across above-ground tissues. Considering to the habitat characteristics of A. squarrosum , we proposed that the enrichment of terpenoids and the functional diversification of terpenoids biosynthesis enzymes were more or less involved into its adaptation to stressful environments of deserts. These results expand the available genetic information underlying terpenoid biosynthesis in A. squarrosum , and contribute to deeper researches on pharmaceutical and eco-agricultural applications in this desert medicinal plant.