The biosynthesis and nutritional uses of carotenoids.

Plants synthesize an amazing diversity of volatile organic compounds (VOCs) that facilitate interactions with their environment, from attracting pollinators and seed dispersers to protecting themselves from pathogens, parasites and herbivores. Recent progress in -omics technologies resulted in the isolation of genes encoding enzymes responsible for the biosynthesis of many volatiles and contributed to our understanding of regulatory mechanisms involved in VOC formation. In this review, we largely focus on the biosynthesis and regulation of plant volatiles, the involvement of floral volatiles in plant reproduction as well as their contribution to plant biodiversity and applications in agriculture via crop-pollinator interactions. In addition, metabolic engineering approaches for both the improvement of plant defense and pollinator attraction are discussed in light of methodological constraints and ecological complications that limit the transition of crops with modified volatile profiles from research laboratories to real-world implementation.

https://nph.onlinelibrary.wiley.com/doi/epdf/10.1111/nph.12145

Biosynthesis, function and metabolic engineering of plant volatile organic compounds.

Carotenoid Metabolism in Plants

Isoprenoid biosynthesis is essential for all living organisms, and isoprenoids are also of industrial and agricultural interest. All isoprenoids are derived from prenyl diphosphate (prenyl-PP) precursors. Unlike isoprenoid biosynthesis in other living organisms, prenyl-PP, as the precursor of all isoprenoids in plants, is synthesized by two independent pathways: the mevalonate (MVA) pathway in the cytoplasm and the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway in plastids. This review focuses on progress in our understanding of how the precursors for isoprenoid biosynthesis are synthesized in the two subcellular compartments, how the underlying pathway gene networks are organized and regulated, and how network perturbations impact each pathway and plant development. Because of the wealth of data on isoprenoid biosynthesis, we emphasize research in Arabidopsis thaliana and compare the synthesis of isoprenoid precursor molecules in this model plant with their synthesis in other prokaryotic and eukaryotic organisms.

Network Analysis of the MVA and MEP Pathways for Isoprenoid Synthesis

Plants synthesize an enormous variety of metabolites that can be classified into two groups based on their function: primary metabolites, which participate in nutrition and essential metabolic processes within the plant, and secondary metabolites (also referred to as natural products), which

Elucidation of the methylerythritol phosphate pathway for isoprenoid biosynthesis in bacteria and plastids. A metabolic milestone achieved through genomics.

Thiolases are ubiquitous enzymes involved in many essential biochemical processes. Biosynthetic thiolases, also known as acetoacetyl-CoA thiolases (AACT), catalyse a reversible Claisen-type condensation of two acetyl-CoA molecules to form acetoacetyl-CoA. Here, we report the characterisation of two genes from Arabidopsis thaliana L., ACT1 and ACT2, which encode two closely related AACT isoforms (AACT1 and AACT2, respectively). Transient expression of constructs encoding AACT1 and AACT2 fused to GFP revealed that the two proteins show a different subcellular localisation. While AACT1 is found in peroxisomes, AACT2 localises in the cytosol and the nucleus. The peroxisomal localisation of AACT1 depends on the presence of a C-terminal peroxisomal targeting sequence (PTS1) motif (Ser-Ala-Leu) not previously found in other organisms. ACT1 and ACT2 genes are also differentially expressed. Whereas ACT2 is expressed at relatively high level in all plant tissues, the expression of ACT1 is restricted to roots and inflorescences and its transcript is present at very low levels. The obtained results are in agreement with the involvement of AACT2 in catalysing the first step of the mevalonate pathway. The metabolic function of AACT1 is not clear at present, although its particular peroxisomal localisation might exclude a role in isoprenoid biosynthesis.

Characterisation of the gene family encoding acetoacetyl-CoA thiolase in Arabidopsis

We introduce modifications to Monte Carlo simulations of the Feynman path integral that improve sampling of localised interactions. The new algorithms generate trajectories in simple background potentials designed to concentrate them about the interaction region, reminiscent of importance sampling. This improves statistical sampling of the system and overcomes a long-time"undersampling problem"caused by the spatial diffusion inherent in Brownian motion. We prove the validity of our approach using previous analytic work on the distribution of values of the Wilson line over path integral trajectories and illustrate the improvements on some simple quantum mechanical systems

pdf/monte-carlo-generation-of-localised-particle-trajectories-1pz40qyk.pdf

Monte Carlo generation of localised particle trajectories

The recently discovered 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway for the biosynthesis of plastid isoprenoids (including carotenoids) is not fully elucidated yet despite its central importance for plant life. It is known, however, that the first reaction completely specific to the pathway is the conversion of 1-deoxy-D-xylulose 5-phosphate (DXP) into MEP by the enzyme DXP reductoisomerase (DXR). We have identified a tomato cDNA encoding a protein with homology to DXR and in vivo activity, and show that the levels of the corresponding DXR mRNA and encoded protein in fruit tissues are similar before and during the massive accumulation of carotenoids characteristic of fruit ripening. The results are consistent with a non-limiting role of DXR, and support previous work proposing DXP synthase (DXS) as the first regulatory enzyme for plastid isoprenoid biosynthesis in tomato fruit. Inhibition of DXR activity by fosmidomycin showed that plastid isoprenoid biosynthesis is required for tomato fruit carotenogenesis but not for other ripening processes. In addition, dormancy was reduced in seeds from fosmidomycin-treated fruit but not in seeds from the tomato yellow ripe mutant (defective in phytoene synthase-1, PSY1), suggesting that the isoform PSY2 might channel the production of carotenoids for abscisic acid biosynthesis. Furthermore, the complete arrest of tomato seedling development using fosmidomycin confirms a key role of the MEP pathway in plant development.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-313x.2001.01089.x

1‐Deoxy‐d‐xylulose 5‐phosphate reductoisomerase and plastid isoprenoid biosynthesis during tomato fruit ripening

1-Deoxy-D-xylulose 5-phosphate reductoisomerase (DXR) catalyzes the first committed step of the 2-C-methyl-D-erythritol 4-phosphate pathway for isoprenoid biosynthesis. In Arabidopsis, DXR is encoded by a single-copy gene. We have cloned a full-length cDNA corresponding to this gene. A comparative analysis of all plant DXR sequences known to date predicted an N-terminal transit peptide for plastids, with a conserved cleavage site, and a conserved proline-rich region at the N terminus of the mature protein, which is not present in the prokaryotic DXR homologs. We demonstrate that Arabidopsis DXR is targeted to plastids and localizes into chloroplasts of leaf cells. The presence of the proline-rich region in the mature Arabidopsis DXR was confirmed by detection with a specific antibody. A proof of the enzymatic function of this protein was obtained by complementation of an Escherichia coli mutant defective in DXR activity. The expression pattern of beta-glucuronidase, driven by the DXR promoter in Arabidopsis transgenic plants, together with the tissue distribution of DXR transcript and protein, revealed developmental and environmental regulation of the DXR gene. The expression pattern of the DXR gene parallels that of the Arabidopsis 1-deoxy-D-xylulose 5-phosphate synthase gene, but the former is slightly more restricted. These genes are expressed in most organs of the plant including roots, with higher levels in seedlings and inflorescences. The block of the 2-C-methyl-D-erythritol 4-phosphate pathway in Arabidopsis seedlings with fosmidomycin led to a rapid accumulation of DXR protein, whereas the 1-deoxy-D-xylulose 5-phosphate synthase protein level was not altered. Our results are consistent with the participation of the Arabidopsis DXR gene in the control of the 2-C-methyl-D-erythritol 4-phosphate pathway.

http://www.plantphysiol.org/content/plantphysiol/129/4/1581.full.pdf

Expression and Molecular Analysis of the Arabidopsis DXR Gene Encoding 1-Deoxy-d-Xylulose 5-Phosphate Reductoisomerase, the First Committed Enzyme of the 2-C-Methyl-d-Erythritol 4-Phosphate Pathway

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Characterisation of the gene family encoding acetoacetyl-CoA thiolase in Arabidopsis

Monte Carlo generation of localised particle trajectories

1‐Deoxy‐d‐xylulose 5‐phosphate reductoisomerase and plastid isoprenoid biosynthesis during tomato fruit ripening

Expression and Molecular Analysis of the Arabidopsis DXR Gene Encoding 1-Deoxy-d-Xylulose 5-Phosphate Reductoisomerase, the First Committed Enzyme of the 2-C-Methyl-d-Erythritol 4-Phosphate Pathway