Exceptionally high percentage of IPP synthesis by Ginkgo biloba IspH is mainly due to Phe residue in the active site

HDR, the last enzyme in the MEP pathway, differently regulates isoprenoid biosynthesis in two woody plants

Dimethylallyl diphosphate (DMADP) and isopentenyl diphosphate (IDP) serves as the universal C5 precursors of isoprenoid biosynthesis in plants. These compounds are formed by the last step of the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway, catalyzed by (E)-4-hydroxy-3-methylbut-2-en-1-yl diphosphate reductase (HDR). In this study, we investigated the major HDR isoforms of two woody plant species, Norway spruce (Picea abies) and gray poplar (Populus × canescens), to determine how they regulate isoprenoid formation. Since each of these species has a distinct profile of isoprenoid compounds, they may require different proportions of DMADP and IDP with proportionally more IDP being needed to make larger isoprenoids. Norway spruce contained two major HDR isoforms differing in their occurrence and biochemical characteristics. PaHDR1 produced relatively more IDP than PaHDR2 and it encoding gene was expressed constitutively in leaves, likely serving to form substrate for production of carotenoids, chlorophylls, and other primary isoprenoids derived from a C20 precursor. On the other hand, Norway spruce PaHDR2 produced relatively more DMADP than PaHDR1 and its encoding gene was expressed in leaves, stems, and roots, both constitutively and after induction with the defense hormone methyl jasmonate. This second HDR enzyme likely forms a substrate for the specialized monoterpene (C10), sesquiterpene (C15), and diterpene (C20) metabolites of spruce oleoresin. Gray poplar contained only one dominant isoform (named PcHDR2) that produced relatively more DMADP and the gene of which was expressed in all organs. In leaves, where the requirement for IDP is high to make the major carotenoid and chlorophyll isoprenoids derived from C20 precursors, excess DMADP may accumulate, which could explain the high rate of isoprene (C5) emission. Our results provide new insights into the biosynthesis of isoprenoids in woody plants under conditions of differentially regulated biosynthesis of the precursors IDP and DMADP.

Adaptation of hydroxymethylbutenyl diphosphate reductase enables volatile isoprenoid production

Volatile isoprenoids produced by plants are emitted in vast quantities into the atmosphere, with substantial effects on global carbon cycling. Yet, the molecular mechanisms regulating the balance between volatile and non-volatile isoprenoid production remain unknown. Isoprenoids are synthesised via sequential condensation of isopentenyl pyrophosphate (IPP) to dimethylallyl pyrophosphate (DMAPP), with volatile isoprenoids containing fewer isopentenyl subunits. The DMAPP:IPP ratio could affect the balance between volatile and non-volatile isoprenoids, but the plastidic DMAPP:IPP ratio is generally believed to be similar across different species. Here we demonstrate that the ratio of DMAPP:IPP produced by hydroxymethylbutenyl diphosphate reductase (HDR/IspH), the final step of the plastidic isoprenoid production pathway, is not fixed. Instead, this ratio varies greatly across HDRs from phylogenetically distinct plants, correlating with isoprenoid production patterns. Our findings suggest that adaptation of HDR plays a previously unrecognised role in determining in vivo carbon availability for isoprenoid emissions, directly shaping global biosphere-atmosphere interactions.

Diatom isoprenoids: Advances and biotechnological potential

Diatoms are among the most productive and ecologically important groups of microalgae in contemporary oceans. Due to their distinctive metabolic and physiological features, they offer exciting opportunities for a broad range of commercial and industrial applications. One such feature is their ability to synthesize a wide diversity of isoprenoid compounds. However, limited understanding of how these molecules are synthesized have until recently hindered their exploitation. Following comprehensive genomic and transcriptomic analysis of various diatom species, the biosynthetic mechanisms and regulation of the different branches of the pathway are now beginning to be elucidated. In this review, we provide a summary of the recent advances in understanding diatom isoprenoid synthesis and discuss the exploitation potential of diatoms as chassis for high-value isoprenoid synthesis.

Isolation and characterization of 4-hydroxy-3-methylbut-2-enyl diphosphate reductase gene from Botryococcus braunii, race B

The B race of a green microalga Botryococcus braunii Kützing produces triterpene hydrocarbons that is a promising source for biofuel. In this algal race, precursors of triterpene hydrocarbons are provided from the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway. The terminal enzyme of this pathway, 4-hydroxy-3-methylbut-2-enyl diphosphate reductase (HDR) is regarded as one of the key enzymes that affect yields of products in terpene biosynthesis. In order to better understand the MEP pathway of the alga, cDNA and genomic clones of HDR were obtained from B. braunii Showa strain. B. braunii HDR (BbHDR) is encoded on a single copy gene including a 1509-bp open reading frame that was intervened by 6 introns. The exon-intron structure of BbHDR genes did not show clear relation to phylogeny, while its amino acid sequence reflected phyla and classes well. BbHDR sequence was distinctive from that of the HDR protein from Escherichia coli in the residues involved in hydrogen-bond network that surrounds substrate. Introduction of BbHDR cDNA into an E. coli HDR deficient mutant resulted in recovery of its auxotrophy. BbHDR expression level was upregulated from the onset of liquid culture to the 24th day after inoculation with a 2.5-fold increase and retained its level in the subsequent period.