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Plant Responses and Mechanisms of Tolerance to Cold Stress
Published in Hasanuzzaman Mirza, Nahar Kamrun, Fujita Masayuki, Oku Hirosuke, Tofazzal M. Islam, Approaches for Enhancing Abiotic Stress Tolerance in Plants, 2019
Aruna V. Varanasi, Nicholas E. Korres, Vijay K. Varanasi
Galactinol synthase is a key enzyme in the synthesis of raffinose oligosaccharides, which catalyzes the first committed step in raffinose synthesis. It is found to play a vital role in plant response to low temperatures through saccharide metabolism, especially the raffinose oligosaccharide pathway, which results in the accumulation of monosaccharides and disaccharides such as glucose, fructose, sucrose, galactinol, melibiose, and raffinose (Hannah et al., 2006; Usadel et al., 2008). Among these sugars, galactinol and raffinose possibly act as scavengers of ROS (Nishizawa et al., 2008), whereas sucrose and other simple sugars likely play a role in the stabilization of cell membranes by interacting with phospholipids and proteins in the plasma membrane, and supporting the structure and function of cell membranes (Uemura and Steponkus, 2003; Yano et al., 2005). In addition, other sugar metabolism enzymes such as sucrose phosphate synthase and invertase are also involved in the cold response. Changes in sugar concentrations catalyzed by yeast invertase in potato plants resulted in a higher tolerance to low temperatures (Deryabin et al., 2005). In Arabidopsis, while the transcript levels of sucrose phosphate synthase are induced by low temperatures, several genes from the invertase family are suppressed (Usadel et al., 2008). On the contrary, in wheat and tomato, invertase ac tivity was found to be upregulated as the temperature decreased, although the response in chilling-tolerant accessions was weaker (Artuso et al., 2000; Vargas et al., 2007).
Multiple Roles of Cardiac Metabolism: New Opportunities for Imaging the Physiology of the Heart
Published in Robert J. Gropler, David K. Glover, Albert J. Sinusas, Heinrich Taegtmeyer, Cardiovascular Molecular Imaging, 2007
The hypothesis finds further support by the observations that insulin promotes tolerance against ischemic cell death via the activation of issue-specific cell-survival pathways in the heart (73). Specifically, activation of PI3 kinase, a downstream target of the insulin receptor substrate (IRS), and activation of protein kinase B/Akt, are mediators of antiapoptotic, cardioprotective signaling through activation of p70s6 kinase and inactivation of proapoptotic peptides. The major mediator is Akt (or protein kinase B). Akt is located at the center of insulin and insulin-like growth factor 1 (IGF1) signaling. As the downstream serine-threonine kinase effector of PI3 kinase, Akt plays a key role in regulating cardiomyocyte growth and survival (74). Overexpression of constitutively active Akt raises myocardial glycogen levels and protects against ischemic damage in vivo and in vitro (75). Not surprisingly, Akt is also a modulator of metabolic substrate utilization (76). Phosphorylation of GLUT4 by Akt promotes its translocation and increases glucose uptake. Although the “insulin hypothesis” is attractive, there is also good evidence showing that the signaling cascade is dependent on the first committed step of glycolysis and translocation of hexokinase to the outer mitochondrial membrane (77,78). These few examples illustrate the fact that any signals detected by metabolic imaging of stressed or failing heart are the product of complex cellular reactions—truly only the tip of an iceberg.
Bioengineering Approach on Terpenoids Production
Published in Dijendra Nath Roy, Terpenoids Against Human Diseases, 2019
The first demonstration of the potential of synthetic biology and metabolic engineering of microbes for commercial production is the synthesis of semi-synthetic artemisinin and its derivatives in microbial systems (Paddon and Keasling, 2014). Artemisinin and its derivatives are the key active drugs for the effective treatment of malaria, and they remain unaffordable for most vulnerable populations. Artemisinin is a sesquiterpene lactone, extracted from dried leaves and inflorescences of A. annua, which is a labour-intensive crop with a lengthy growing cycle. Approximately 1 ha of A. annua plants can yield only ∼5 kg of artemisinin, promoting the need to develop additional source of artemisinin production to meet the rising global demands (Hale et al. 2007). The first committed step of artemisinin biosynthesis is catalysed by terpene synthase enzyme amorphadiene synthase (ADS), which converts FPP to amorphadiene (sesquiterpenoid). Amorphadiene undergoes enzymatic oxidation to form artemisinic acid or dihydroartemisinic acid. Dihydroartemisinic acid is converted to artemisinin (Paddon and Keasling 2014). The initial stage towards microbial production of amorphadiene involved E. coli. The heterologous expression of MVA genes from yeast (S. cerevisiae) and a codon-optimized ADS gene from A. Annua with optimized fermentation conditions yielded about 0.5 g/L amorphadiene (Newman et al. 2006). The MVA pathway was considered as a rate-limiting step and expression of each gene of this pathway was studied and manipulated. This approach identified that reduced expression of HMGS and truncated tHMGR can lead to a sevenfold increase in MVA production (Pfleger et al. 2006). Metabolite analysis identified that the accumulation of intermediate HMG-CoA was deleterious and that this was mitigated by the introduction of an additional copy of HMGR, which enhanced yields (Pitera et al. 2007). Additional strain engineering and improved fermentation techniques have increased the titre of amorphadiene to a commercially relevant titre of >25 g/L (Tsuruta et al. 2009).
Flavonoids – flowers, fruit, forage and the future
Published in Journal of the Royal Society of New Zealand, 2023
Nick W. Albert, Declan J. Lafferty, Sarah M. A. Moss, Kevin M. Davies
The biosynthesis of flavonoids begins with the aromatic amino acid phenylalanine, and is part of the larger phenylpropanoid biosynthesis pathway, which produces lignin, phenolic acids and volatiles, in addition to flavonoids. The first committed step to flavonoid biosynthesis (Figure 1B, refer for enzyme abbreviations) is catalysed by CHS, after which a series of isomerisation (CHI), hydroxylation (F3H, F3′H, F3′5′H), reduction (DFR, LAR, ANR) or oxidation (FLS, ANS) reactions occur to generate various flavonoid compounds, which are further modified or ‘decorated’ by glycosylation, methylation or acylation. Martin and Gerats (1993) coined the term ‘early’ and ‘late’ flavonoid biosynthesis genes. The ‘early biosynthetic genes’ were steps that did not show substantially reduced expression in anthocyanin regulatory mutants (typically CHS, CHI, F3H), while the ‘late biosynthetic genes’ showed substantial or a complete loss of expression (DFR, ANS, UFGT). This term has been widely adopted in the literature, but is often misinterpreted to suggest the early biosynthetic genes are not targeted by regulators of anthocyanin biosynthesis. More recently, studies have identified genes encoding non-enzymatic biosynthetic proteins, such as CHI-Like and the PR10 proteins, which are necessary for efficient production of flavonoids (Muñoz et al. 2010; Morita et al. 2014; Ban et al. 2018; Clayton et al. 2018; Berland et al. 2019), possibly by binding metabolite intermediates and channelling them to enzymes (e.g. CHS) efficiently, with correct stereochemistry (Dastmalchi 2021). The regulation of different branches of flavonoid production is complex, nuanced, and involves redundant regulation of some biosynthetic genes, particularly genes common to multiple pathways. Central to the regulation of flavonoids are R2R3-MYB transcription factors, which have diversified into sub-groups that have specialised in regulating the production of different metabolites (Figure 2A).
The enhanced biomass and lipid accumulation in algae with an integrated treatment strategy by waste molasses and Mg2+ addition
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2020
Xunzan Dong, Li Huang, Tao Li, Jun-Wei Xu, Peng Zhao, Xuya Yu
As demonstrated in Figure 2, lipid content and productivity were enhanced following the addition of 0–800 μM Mg2+. Further increases in the Mg2+ concentration to 1600 μM resulted in a slight reduction in lipid levels to 54.78% (Figure 2). The highest values for lipid levels and lipid productivity were 59.58% and 11.21 mg L−1 d−1, respectively, in cultures supplemented with 800 μM Mg2+, and these values were 1.26- and 2.28-times higher than those in the control condition, respectively. However, according to Sydney et al., magnesium consumption by all microalgae was increased compared with the levels the necessary for chlorophyll production, suggesting that this nutrient plays other important roles in microalgae metabolism (Sydney et al. 2010). In general, under limited nutrient conditions, algae growth was reduced, but algae effectively accumulated lipids. For instance, increased neutral lipids were detected in the Mg-free medium used to grow Chlamydomonas and Chlorella (Deng, Fei, and Li 2011). Unexpectedly, the peak values of DCW and lipids were observed with high Mg2+ in concentrations this study. Previous studies have demonstrated that lipid accumulation of Monoraphidium sp. FXY-10 is stimulated by an increase in the magnesium concentration in BG-11 medium (Huang et al. 2014). Similarly, the addition of 100 mg L−1 magnesium resulted in a 1.44-fold increase in lipid levels in the media (Gorain, Bagchi, and Mallick 2013). Additionally, Scenedesmus sp. with increased lipid content was obtained when the concentration of Mg2+ increased from 0 to 0.73 g L−1 (Ren et al. 2014), indicating that Mg2+ may augment lipid accumulation in microalgae. Magnesium ions promote the activity of acetyl-CoA, which regulates the first committed step of algae lipid biosynthesis and are also required in the chloroplast pyruvate dehydrogenase complex, which provides acetyl-CoA and NADH for fatty acid synthesis (Singh et al. 2016). Thus, an increased Mg2+ concentration in medium could promote not only cell growth but also lipid accumulation in algae.