Dissection of the phytohormonal regulation of trichome formation and biosynthesis of the antimalarial compound artemisinin in Artemisia annua plants

Abstract

Summary Biosynthesis of the sesquiterpene lactone and potent antimalarial drug artemisinin occurs in glandular trichomes of Artemisia annua plants and is subjected to a strict network of developmental and other regulatory cues. The effects of three hormones, jasmonate, gibberellin and cytokinin, were studied at the structural and molecular levels in two different A. annua chemotypes by microscopic analysis of gland development, and by targeted metabolite and transcript profiling. Furthermore, a genome‐wide cDNA‐amplified fragment length polymorphism (AFLP)‐based transcriptome profiling was carried out of jasmonate‐elicited leaves at different developmental stages. Although cytokinin and gibberellin positively affected at least one aspect of gland formation, these two hormones did not stimulate artemisinin biosynthesis. Only jasmonate simultaneously promoted gland formation and coordinated transcriptional activation of biosynthetic gene expression, which ultimately led to increased sesquiterpenoid accumulation with chemotype‐dependent effects on the distinct pathway branches. Transcriptome profiling revealed a trichome‐specific fatty acyl‐ coenzyme A reductase, trichome‐specific fatty acyl‐CoA reductase 1 (TFAR1), the expression of which correlates with trichome development and sesquiterpenoid biosynthesis. TFAR1 is potentially involved in cuticular wax formation during glandular trichome expansion in leaves and flowers of A. annua plants. Analysis of phytohormone‐modulated transcriptional regulons provides clues to dissect the concerted regulation of metabolism and development of plant trichomes.

OSC2 and CYP716A14v2 Catalyze the Biosynthesis of Triterpenoids for the Cuticle of Aerial Organs of Artemisia annua

“…Triterpenoid genes were found to be induced by jasmonate, cytokinin, and gibberellin (this study), whereas artemisinin genes were induced only by jasmonate and repressed by both cytokinin and gibberellin (Maes et al, 2011). Notably, all three phytohormones can also induce the formation of filamentous trichomes, whereas only jasmonate can stimulate the formation and maturation of the glandular trichomes (Maes et al, 2011), which correlates well with the respective enrichment of the triterpenoid and artemisinin transcripts in these organs.…”

“…Pentacyclic triterpenoids, mainly derived from a-amyrin, b-amyrin, and lupeol, often occur in the leaf, flower, and fruit cuticular wax layers of many plants (Bringe et al, 2006;Murata et al, 2008;Wang et al, 2011;Szakiel et al, 2013). Therefore, we analyzed the triterpene content of the cuticular wax layer from flower buds and leaves of two A. annua cultivars: Anamed A3, the cultivar from which OSC2 was isolated, and Meise, a low artemisinin-producing cultivar that we previously used to study phytohormonal regulation of artemisinin biosynthesis (Maes et al, 2011).…”

“…Various mechanisms have been recognized to be involved in its regulation, including the transcriptional activation of entire pathways by a common trigger, which allows the synchronized action of the pathway proteins (Maes et al, 2011;De Geyter et al, 2012;Moses et al, 2013). Therefore, coexpression and coregulation of candidate genes can be used as an indication of their possible involvement in a common biosynthetic process.…”

“…This was performed by analyzing their expression profile in a sample set generated in previous research (Maes et al, 2011), in which seedlings of the A. annua Meise cultivar were treated with different hormones, namely, jasmonate, the synthetic cytokinin 6-benzylaminopurine (BAP), and gibberellic acid (GA 3 ). Two general observations could be drawn from this analysis ( Figure 5).…”

Chitosan oligosaccharide and salicylic acid up-regulate gene expression differently in relation to the biosynthesis of artemisinin in Artemisia annua L.

“…In plants, artemisinin is biosynthesized and stored in specialized anatomical structures, termed glandular trichomes, on leaves, stems and inflorescences [6]. The amount of artemisinin in A. annua plants depends primarily on glandular trichome density and biosynthesis capacity in glands; thus the performance of the biosynthetic pathways leading to artemisinin is important to understand.…”