The Arabidopsis thaliana Type I Isopentenyl Diphosphate Isomerases Are Targeted to Multiple Subcellular Compartments and Have Overlapping Functions in Isoprenoid Biosynthesis

Abstract

To form the building blocks of isoprenoids, isopentenyl diphosphate (IPP) isomerase activity, which converts IPP to dimethylallyl diphosphate (DMAPP), appears to be necessary in cytosol, plastids, and mitochondria. Arabidopsis thaliana contains only two IPP isomerases (Isopentenyl Diphosphate Isomerase1 [IDI1] and IDI2). Both encode proteins with N-terminal extensions similar to transit peptides and are expressed in all organs, with IDI1 less abundant than IDI2. Examination of enhanced green fluorescent protein fusions established that IDI1 is mainly in the plastid, whereas IDI2 is mainly in the mitochondria. Both proteins are also in the cytosol as a result of their translation from naturally occurring shorter transcripts lacking transit peptides, as demonstrated by 59 rapid amplification of cDNA ends cloning. IPP isomerase activity in the cytosol was confirmed by uniform labeling of IPP-and DMAPP-derived units of the cytoplasmic isoprenoid product, sitosterol, when labeled mevalonate was administered. Analysis of mutant lines showed that double mutants were nonviable, while homozygous single mutants had no major morphological or chemical differences from the wild type except for flowers with fused sepals and underdeveloped petals on idi2 mutants. Thus, each of the two Arabidopsis IPP isomerases is found in multiple but partially overlapping subcellular locations, and each can compensate for the loss of the other through partial redundancy in the cytosol.

Carotenoid Biosynthesis in Arabidopsis: A Colorful Pathway

“…Unlike the MEP pathway enzymes, IDI is encoded by two genes in Arabidopsis, IPI1/IPPI1/IDI1 (At5g16440) and IPI2/IPPI2/IDI2 (At3g02780). Although the simultaneous production of both IPP and DMAPP by the MEP pathway is expected to make the presence of a plastidial IDI activity dispensable, both IDI1 and IDI2 isoforms have been found in chloroplasts by using GFP fusions and proteomic approaches, the latter suggesting the presence of IDI1 in the stroma and IDI2 in membranes (Phillips et al, 2008a;Sapir-Mir et al, 2008;Joyard et al, 2009). A plastidial isomerase might ensure that an appropriate ratio between IPP and DMAPP is maintained for isoprenoid biosynthesis.…”

The Small Subunit of Snapdragon Geranyl Diphosphate Synthase Modifies the Chain Length Specificity of Tobacco Geranylgeranyl Diphosphate Synthase in Planta

“…Metabolic flux through these pathways can differ dramatically, and the flux through the MEP pathway often exceeds that of the MVA (McCaskill and Croteau, 1995;Dudareva et al, 2005;Wu et al, 2006). It was reported that IPP and perhaps DMAPP could be exchanged between different compartments, particularly in the direction from plastids to cytosol (Hemmerlin et al, 2003;Laule et al, 2003;Schuhr et al, 2003;Dudareva et al, 2005;Phillips et al, 2008), raising a question about the relative contribution of each pathway to the biosynthesis of the various classes of terpenoids. Trafficking of isoprenoid intermediates between organelles, likely mediated by specific metabolite transporters (Bick and Lange, 2003), depends on the plant species, tissue, and physiological state of the plant (Steliopoulos et al, 2002;Dudareva et al, 2005;Hampel et al, 2005aHampel et al, , 2005b.…”

The genetic basis of foliar terpene yield: Implications for breeding and profitability of Australian essential oil crops

“…Most plants have two copies of ippi (Table 1), which are thought to have specialised but overlapping functions (Cunningham and Gantt 2000;Nakamura et al 2001;Okada et al 2008;Phillips et al 2008). In Arabidopsis, one copy is expressed more strongly in the cytosol (termed idi2) and the other more strongly in the plastid (termed idi1).…”

“…In Arabidopsis, one copy is expressed more strongly in the cytosol (termed idi2) and the other more strongly in the plastid (termed idi1). However, knockouts mutants of each gene in Arabidopsis have shown that each idi gene can compensate for the other in both parts of the cell and that there is no significant difference in terpenes produced or growth phenotypes by either idi1 or idi2 knockouts when compared to the wild type (Okada et al 2008;Phillips et al 2008). IPP and DMAPP form the backbone of all plant terpenes, apart from isoprene which is synthesized directly from IPP and the ratio of IPP : DMAPP is thought to be important in allocating resources to the synthesis of the different classes of terpene.…”

“…The ratio of IPP to DMAPP determines which of these prenyl synthases will be most active; gpps works most efficiently with a IPP : DMAPP ratio of 1 : 1 (Bouvier et al 2000), ggpps works most efficiently with a ratio of 3 : 1 (Allen and Banthorpe 1981;Ohnuma et al 1989) and fpps works most efficiently with a ratio of 2 : 1 (Hugueney and Camara 1990). The key intermediate gene ippi is responsible for controlling the IPP : DMAPP ratio and may have an important role in regulating the proportion of the different classes of terpene that are synthesised (Phillips et al 2008). Wildung and Croteau (2005) showed that when both copies of ippi were downregulated in peppermint, (which primarily produces monoterpenes), there was a large increase in the concentration of foliar sesquiterpenes.…”