The truncated AaActin1 promoter is a candidate tool for metabolic engineering of artemisinin biosynthesis in Artemisia annua L

Improvement and application of vacuum-infiltration system in tomato

The Agrobacterium-mediated transient expression system has been developed and applied to various plants as an alternative to stable transformation. However, its application in tomatoes is still limited due to low expression efficiency. In this study, we describe an improved vacuum-infiltration system that can be used in both tomato fruits and leaves. Notably, this study is the first report of vacuum infiltration in attached tomato fruits. The feasibility of the improved vacuum-infiltration system in Micro-Tom tomato was confirmed by various assays, including multiple fluorescent protein expression analysis, β-glucuronidase activity analysis, and RUBY reporter visualization. Subsequently, the improved vacuum-infiltration system was successfully applied to tomato biotechnology research. Herein, a trichome-specific promoter in tomato was identified that can drive the directional synthesis of specific plant natural products (PNPs). Additionally, based on the assessment results of the improved vacuum-infiltration system, we obtained a flavonoid-rich tomato variety through the stable transformation of AmRosea and AmDelila. In a significant practical application, we successfully synthesized the high-value scutellarin in tomato, which provides an alternative route for the production of PNPs from plants. In addition, the improved vacuum-infiltration system has been demonstrated to be suitable for commercial tomato varieties ('Emerald' and 'Provence') as well. The improved vacuum-infiltration system not only speeds up fundamental and applied research in tomato but also offers an additional powerful tool for advancing tomato synthetic biology research.

A transcription factor of SHI family AaSHI1 activates artemisinin biosynthesis genes in Artemisia annua

BACKGROUND

Transcription factors (TFs) of plant-specific SHORT INTERNODES (SHI) family play a significant role in regulating development and metabolism in plants. In Artemisia annua, various TFs from different families have been discovered to regulate the accumulation of artemisinin. However, specific members of the SHI family in A. annua (AaSHIs) have not been identified to regulate the biosynthesis of artemisinin.

RESULTS

We found five AaSHI genes (AaSHI1 to AaSHI5) in the A. annua genome. The expression levels of AaSHI1, AaSHI2, AaSHI3 and AaSHI4 genes were higher in trichomes and young leaves, also induced by light and decreased when the plants were subjected to dark treatment. The expression pattern of these four AaSHI genes was consistent with the expression pattern of four structural genes of artemisinin biosynthesis and their specific regulatory factors. Dual-luciferase reporter assays, yeast one-hybrid assays, and transient transformation in A. annua provided the evidence that AaSHI1 could directly bind to the promoters of structural genes AaADS and AaCYP71AV1, and positively regulate their expressions. This study has presented candidate genes, with AaSHI1 in particular, that can be considered for the metabolic engineering of artemisinin biosynthesis in A. annua.

CONCLUSIONS

Overall, a genome-wide analysis of the AaSHI TF family of A. annua was conducted. Five AaSHIs were identified in A. annua genome. Among the identified AaSHIs, AaSHI1 was found to be localized to the nucleus and activate the expression of structural genes of artemisinin biosynthesis including AaADS and AaCYP71AV1. These results indicated that AaSHI1 had positive roles in modulating artemisinin biosynthesis, providing candidate genes for obtaining high-quality new A. annua germplasms.

The AaBBX21-AaHY5 module mediates light-regulated artemisinin biosynthesis in Artemisia annua L

The sesquiterpene lactone artemisinin is an important anti-malarial component produced by the glandular secretory trichomes of sweet wormwood (Artemisia annua L.). Light was previously shown to promote artemisinin production, but the underlying regulatory mechanism remains elusive. In this study, we demonstrate that ELONGATED HYPOCOTYL 5 (HY5), a central transcription factor in the light signaling pathway, cannot promote artemisinin biosynthesis on its own, as the binding of AaHY5 to the promoters of artemisinin biosynthetic genes failed to activate their transcription. Transcriptome analysis and yeast two-hybrid screening revealed the B-box transcription factor AaBBX21 as a potential interactor with AaHY5. AaBBX21 showed a trichome-specific expression pattern. Additionally, the AaBBX21-AaHY5 complex cooperatively activated transcription from the promoters of the downstream genes AaGSW1, AaMYB108, and AaORA, encoding positive regulators of artemisinin biosynthesis. Moreover, AaHY5 and AaBBX21 physically interacted with the A. annua E3 ubiquitin ligase CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1). In the dark, AaCOP1 decreased the accumulation of AaHY5 and AaBBX21 and repressed the activation of genes downstream of the AaHY5-AaBBX21 complex, explaining the enhanced production of artemisinin upon light exposure. Our study provides insights into the central regulatory mechanism by which light governs terpenoid biosynthesis in the plant kingdom.

Advanced metabolic engineering strategies for increasing artemisinin yield in Artemisia annua L

Artemisinin, also known as 'Qinghaosu', is a chemically sesquiterpene lactone containing an endoperoxide bridge. Due to the high activity to kill Plasmodium parasites, artemisinin and its derivatives have continuously served as the foundation for antimalarial therapies. Natural artemisinin is unique to the traditional Chinese medicinal plant Artemisia annua L., and its content in this plant is low. This has motivated the synthesis of this bioactive compound using yeast, tobacco, and Physcomitrium patens systems. However, the artemisinin production in these heterologous hosts is low and cannot fulfil its increasing clinical demand. Therefore, A. annua plants remain the major source of this bioactive component. Recently, the transcriptional regulatory networks related to artemisinin biosynthesis and glandular trichome formation have been extensively studied in A. annua. Various strategies including (i) enhancing the metabolic flux in artemisinin biosynthetic pathway; (ii) blocking competition branch pathways; (iii) using transcription factors (TFs); (iv) increasing peltate glandular secretory trichome (GST) density; (v) applying exogenous factors; and (vi) phytohormones have been used to improve artemisinin yields. Here we summarize recent scientific advances and achievements in artemisinin metabolic engineering, and discuss prospects in the development of high-artemisinin yielding A. annua varieties. This review provides new insights into revealing the transcriptional regulatory networks of other high-value plant-derived natural compounds (e.g., taxol, vinblastine, and camptothecin), as well as glandular trichome formation. It is also helpful for the researchers who intend to promote natural compounds production in other plants species.

AaABI5 transcription factor mediates light and abscisic acid signaling to promote anti-malarial drug artemisinin biosynthesis in Artemisia annua

Artemisia annua, a member of the Asteraceae family, remains the primary source of artemisinin. However, the artemisinin content in the existing varieties of this plant is very low. In this study, we found that the environmental factors light and phytohormone abscisic acid (ABA) could synergistically promote the expression of artemisinin biosynthetic genes. Notably, the increased expression levels of those genes regulated by ABA depended on light. Gene expression analysis found that AaABI5, a transcription factor belonging to the basic leucine zipper (bZIP) family, was inducible by the light and ABA treatment. Analysis of AaABI5-overexpressing and -suppressing lines suggested that AaABI5 could enhance artemisinin biosynthesis and activate the expression of four core biosynthetic genes. In addition, the key regulator of light-induced artemisinin biosynthesis, AaHY5, could bind to the promoter of AaABI5 and activate its expression. In conclusion, our results demonstrated that AaABI5 acts as an important molecular junction for the synergistic promotion of artemisinin biosynthesis by light and ABA signals, which provides a candidate gene for developing new germplasms of high-quality A. annua.