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Summary: Artemisinin, a sesquiterpene lactone widely used in malaria treatment, was discovered in the medicinal plant Artemisia annua. The biosynthesis of artemisinin is efficiently regulated by jasmonate (JA) and abscisic acid (ABA) via regulatory factors. However, the mechanisms linking JA and ABA signalling with artemisinin biosynthesis through an associated regulatory network of downstream transcription factors (TFs) remain enigmatic. Here we report AaTCP15, a JA and ABA dual‐responsive teosinte branched1/cycloidea/proliferating (TCP) TF, which is essential for JA and ABA‐induced artemisinin biosynthesis by directly binding to and activating the promoters of DBR2 and ALDH1, two genes encoding enzymes for artemisinin biosynthesis. Furthermore, AaORA, another positive regulator of artemisinin biosynthesis responds to JA and ABA, interacts with and enhances the transactivation activity of AaTCP15 and simultaneously activates AaTCP15 transcripts. Hence, they form an AaORA‐AaTCP15 module to synergistically activate DBR2, a crucial gene for artemisinin biosynthesis. More importantly, AaTCP15 expression is activated by the multiple reported JA and ABA‐responsive TFs that promote artemisinin biosynthesis. Among them, AaGSW1 acts at the nexus of JA and ABA signalling to activate the artemisinin biosynthetic pathway and directly binds to and activates the AaTCP15 promoter apart from the AaORA promoter, which further facilitates formation of the AaGSW1‐AaTCP15/AaORA regulatory module to integrate JA and ABA‐mediated artemisinin biosynthesis. Our results establish a multilayer regulatory network of the AaGSW1‐AaTCP15/AaORA module to regulate artemisinin biosynthesis through JA and ABA signalling, and provide an interesting avenue for future research exploring the special transcriptional regulation module of TCP genes associated with specialized metabolites in plants. [ABSTRACT FROM AUTHOR]

Artemisinin-based therapies are the only effective treatment for malaria, which reached to 219 million cases and killed 435,000 people in 2017. To meet the growing demand for artemisinin and make it accessible to the poorest, genetic engineering of Artemisia annua becomes one of the most promising approaches to improve artemisinin yield. In this work, AabZIP9 transcription factor has been identified and characterized. The expression profile of AabZIP9 revealed that it was clustered with the artemisinin specific biosynthetic pathway genes ADS , CYP71AV1 , DBR2 , and ALDH1. Furthermore, the transiently dual-LUC analysis showed that the activation of ADS promoter was enhanced by AabZIP9. Meanwhile, yeast one-hybrid assay showed that AabZIP9 was able to bind to the "ACGT" cis -element present in both ADS and CYP71AV1 promoters. AabZIP9 gene was driven by the constitutive CaMV35S promoter and the glandular trichome specific CYP71AV1 promoter and stably transformed into A. annua plants. The transcript level of AabZIP9 was increased in both of the 35S and CYP71AV1 driven transgenic plants compared with the wild type or GUS control plants. All the transgenic A. annua plants overexpressing AabZIP9 showed elevated transcript level of ADS , but the transcription levels of CYP71AV1 , DBR2 , and ALDH1 have no significant change in both types of transgenic plants. The significantly upregulated ADS promoted the accumulation of artemisinin, dihydroartemisinic acid, and artemisinic acid biosynthesis in the transgenic A. annua plants. These results suggest that AabZIP9 can positively regulate the biosynthesis of artemisinin. [ABSTRACT FROM AUTHOR]

Artemisinin, the frontline drug against malaria, is a sesquiterpenoid extracted from Artemisia annua. Light has been proposed to play an important role in the activation of artemisinin biosynthesis. Here, we report the basic leucine zipper transcription factor (TF) AaHY5 as a key regulator of light-induced biosynthesis of artemisinin. We show that AaHY5 transcription overlaps with that of artemisinin biosynthesis genes in response to light and in A. annua tissues. Analysis of AaHY5 overexpression and RNAi-suppression lines suggests that AaHY5 is a positive regulator of the expression of artemisinin biosynthesis genes and accumulation of artemisinin. We show that AaHY5 complements the hy5 mutant in Arabidopsis thaliana. Our data further suggest that AaHY5 interacts with AaCOP1, the ubiquitin E3 ligase CONSTITUTIVE PHOTOMORPHOGENIC1 in A. annua. In yeast one-hybrid and transient expression assays, we demonstrate that AaHY5 acts via the TF GLANDULAR TRICHOME-SPECIFIC WRKY 1 (AaGSW1) in artemisinin regulation. In summary, we present a novel regulator of artemisinin gene expression and propose a model in which AaHY5 indirectly controls artemisinin production in response to changing light conditions. [ABSTRACT FROM AUTHOR]

Artemisia annua is the only natural source of the sesquiterpenoid artemisinin, which is widely used to treat malaria. The phytohormone jasmonic acid (JA) can significantly promote artemisinin biosynthesis in A. annua. AabHLH1 can bind and activate artemisinin biosynthetic genes, such as AaADS and AaCYP71AV1. In this study, we proved that AabHLH1 was responsive to MeJA treatment and highly expressed in glandular trichome‐enriched tissues, and that its expression profile was similar to that of AaADS. Yeast two‐hybrid assays showed that AabHLH1 interacted with all nine AaJAZ proteins in A. annua. Functional analysis with transgenic plants showed that several artemisinin biosynthetic genes were upregulated in AabHLH1‐OE transgenic A. annua lines and downregulated in AabHLH1‐EAR lines; furthermore, the artemisinin content was increased in the AabHLH1‐OE lines and decreased in the AabHLH1‐EAR lines. These results demonstrate that the JA‐induced AabHLH1 positively regulates artemisinin biosynthesis by regulating the biosynthetic genes, and thus provide new insight into the regulatory mechanism of JA‐induced artemisinin biosynthesis in A. annua. [ABSTRACT FROM AUTHOR]