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Engineering the Plant Cell Factory for Artemisinin Production
Published in Tariq Aftab, M. Naeem, M. Masroor, A. Khan, Artemisia annua, 2017
Mauji Ram, Himanshu Misra, Ashish Bharillya, Dharam Chand Jain
The functions of an increasing number of plant transcription factors are being elucidated, and many of these factors have been found to impact flux through metabolic pathways. Since transcription factors, as opposed to most structural genes, tend to control multiple steps of pathways, they have emerged as powerful tools for the manipulation of complex metabolic pathways in plants. The importance of transcription factors in the regulation of the flavonoid pathway suggests that they may play an equally important role in regulating other pathways of plant secondary metabolism (Broun et al., 2006). In several species, a relevant observation is the fact that terpenoid accumulation is preceded by the coordinated induction of several pathway genes. It is likely that several aspects of terpenoid metabolism are regulated at the level of gene expression, while relatively little is known of the transcription factors involved. The first direct evidence of transcription factor control over terpenoid pathway gene expression was observed in Catharanthus cells overexpressing (mono) terpenoid indole alkaloid (TIA) pathway activator ORCA3 (Van der Fits and Memelink, 2000). Analysis of the transcript levels showed that, in addition to TIA pathway genes, the gene encoding DXS was also induced. Although induction was found to be significant, it was also fairly limited. G10H encoding geraniol 10-hydroxylase, another gene in the monoterpene branch of the pathway, which was monitored in this experiment, was not affected. These observations suggest a role for ORCA3 in regulating terpenoid as well as TIA biosynthesis, although additional factors are likely to be involved (van der Fits and Memelink 2000). Recently, Ma et al. (2009) isolated and characterized AaWRKY1 , an A. annua L. transcription factor that regulated the ADS gene, a key gene of artemisinin biosynthesis. Promoters of ADS contain two reverse-oriented TTGACC W-box cis-acting elements, which are binding sites of WRKY transcription factors. A full-length cDNA (AaWRKY1 ) was isolated from a cDNA library of the GSTs in which artemisinin is synthesized and sequestered. AaWRKY1 and ADS genes were highly expressed in GSTs and both were strongly induced by methyl jasmonate and chitosan. Ma et al. (ibid) also demonstrated that AaWRKY1 has a similar propensity. Transient expression of AaWRKY1 activated the expression of HMGR , ADS , CYP71AV1 , and DBR2 of the artemisinin biosynthesis pathway. It is possible that the W-box also existed in the promoters of CYP71AV1 , HMGR , and DBR2 in A. annua L. Indeed, the W-box has been found in the promoter of cytochrome P450 genes of many other plants such as Arabidopsis (Narusaka et al., 2004), Camellia japonica (Kato et al., 2007), and cotton (Xu et al., 2004), while two W-box elements were also found in the HMGR1 promoter of Camptotheca acuminate (Burnett et al., 1993).
Transcriptome sequencing of Salvia miltiorrhiza after infection by its endophytic fungi and identification of genes related to tanshinone biosynthesis
Published in Pharmaceutical Biology, 2019
Yan Jiang, Lei Wang, Shaorong Lu, Yizhe Xue, Xiying Wei, Juan Lu, Yanyan Zhang
In the response to the induction process (Figure 3), which was induced by the endophytic fungi, in the host S. miltiorrhiza, eight differential genes, including CNGC (cyclic nucleotide-gated channel), CDPK (calcium-dependent protein kinase [EC:2.7.11.1]), Rboh (respiratory burst oxidase), CaM (calmodulin), WRKY33 (WRKY transcription factor), MAP2K1/MEK1 (mitogen-activated protein kinase kinase 1 [EC:2.7.12.2]), SUGT1/SGT1 (suppressor of G2 allele of SKP1) and HSP90A/htpG (molecular chaperone HtpG), all showed upregulated expression. CNGC is a non-selective cation channel and is a component of the signal transduction pathway in plant systems (Jha et al. 2016). When plant is induced by its endophytic fungi, the CNGC channels will open and Ca2+ influx occurs (Verret et al. 2010; Ma 2011). Therefore, on one hand, CaM activation causes feedback inhibition on CNGC activities and prevents a rapid increase of intracellular Ca2+ concentrations. On the other hand, CDPK activation (Yoon et al. 1999) leads to the phosphorylation of downstream target proteins such as Rboh (Kobayashi et al. 2006; Suzuki et al. 2011). The WRKY protein is one of the substrates of the mitogen-activated protein (MAP) kinase signalling cascade reaction (Mao et al. 2011; Zhou et al. 2015). Therefore, the WRKY transcription factor can be inferred to activate WRKY regulatory genes, especially defence-related genes. Comprehensive analyses showed that certain defence-response reactions occur in host plants at the initial stage of induction by the endophytic fungi.