Plant and Cell Physiology Advance Access originally published online on February 26, 2008
Plant and Cell Physiology 2008 49(4):604-616; doi:10.1093/pcp/pcn032
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Genetic Evidence for the Role of Isopentenyl Diphosphate Isomerases in the Mevalonate Pathway and Plant Development in Arabidopsis
1Biotechnology Research Center, The University of Tokyo, Yayoi, Bunkyo-ku, Tokyo, 113-8657 Japan
2RIKEN Plant Science Center, Tsurumi-ku, Yokohama, Kanagawa, 230-0045 Japan
3Institute of Symbiotic Science and Technology, Tokyo University of Agriculture and Technology, Fuchu, Tokyo, 183-8509 Japan
*Corresponding author: E-mail, ukokada{at}mail.ecc.u-tokyo.ac.jp; Fax, +81-35841-8070.
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Abstract |
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Isopentenyl/dimethylallyl diphosphate isomerase (IPI) catalyzes the interconversion of isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP), which are the universal C5 units of isoprenoids. In plants, IPP and DMAPP are synthesized via the cytosolic mevalonate (MVA) and plastidic methylerythritol phosphate (MEP) pathways, respectively. However, the role of IPI in each pathway and in plant development is unknown due to a lack of genetic studies using IPI-defective mutants. Here, we show that the atipi1atipi2 double mutant, which is defective in two Arabidopsis IPI isozymes, exhibits dwarfism and male sterility under long-day conditions and decreased pigmentation under continuous light, whereas the atipi1 and atipi2 single mutants are phenotypically normal. We also show that the sterol and ubiquinone levels in the double mutant are <50% of those in wild-type plants, and that the male-sterile phenotype is chemically complemented by squalene, a sterol precursor. In vivo isotope labeling experiments using the atipi1atipi2 double mutant revealed a decrease in the incorporation of MVA (in its lactone form) into sterols, with no decrease in the incorporation of MEP pathway intermediates into tocopherol. These results demonstrate a critical role for IPI in isoprenoid biosynthesis via the MVA pathway, and they imply that IPI is essential for the maintenance of appropriate levels of IPP and DMAPP in different subcellular compartments in plants.
Keywords: Dimethylallyl diphosphate - IPP isomerase - Isopentenyl diphosphate - MEP pathway - MVA pathway
Abbreviations: ABRC, Arabidopsis Biological Resource Center; CaMV, cauliflower mosaic virus; DMAPP, dimethylallyl diphosphate; DX, 1-deoxy-D-xylulose; DXR, DX-5-phosphate reductoisomerase; FPP, farnesyl diphosphate; GC-MS, gas chromatography–mass spectrometry; GFP, green fluorescent protein; GGPP, geranylgeranyl diphosphate; GS, glutamine synthetase; HMG-CoA, 3-hydroxy-3-methylglutalyl coenzyme A; IPP, isopentenyl diphosphate; IPI, isopentenyl/dimethylallyl diphosphate isomerase; LD, long-day; MEP, 2-C-methyl-D-erythritol 4-phosphate; MS, Murashige–Skoog; MVA, mevalonate; MVL, mevalonolactone; QRT–PCR, quantitative reverse transcription–PCR; TMRI, Torrey Mesa Research Institute; TMS, trimethylsilyl; UTR, untranslated region.
(Received November 18, 2007; Accepted February 20, 2008)
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