The subcellular localization of two isopentenyl diphosphate isomerases in rice suggests a role for the endoplasmic reticulum in isoprenoid biosynthesis
Both OsIPPI1 and OsIPPI2 enzymes are found in the endoplasmic reticulum, providing novel important insights into the role of this compartment in the synthesis of MVA pathway isoprenoids.
Isoprenoids are synthesized from the precursor’s isopentenyl diphosphate (IPP) and dimethylallyl diphosphosphate (DMAPP), which are interconverted by the enzyme isopentenyl diphosphate isomerase (IPPI). Many plants express multiple isoforms of IPPI, the only enzyme shared by the mevalonate (MVA) and non-mevalonate (MEP) pathways, but little is known about their specific roles. Rice (Oryza sativa) has two IPPI isoforms (OsIPPI1 and OsIPPI2). We, therefore, carried out a comprehensive comparison of IPPI gene expression, protein localization, and isoprenoid biosynthesis in this species. We found that OsIPPI1 mRNA was more abundant than OsIPPI2 mRNA in all tissues, and its expression in de-etiolated leaves mirrored the accumulation of phytosterols, suggesting a key role in the synthesis of MVA pathway isoprenoids. We investigated the subcellular localization of both isoforms by constitutively expressing them as fusions with synthetic green fluorescent protein. Both proteins localized to the endoplasmic reticulum (ER) as well as peroxisomes and mitochondria, whereas only OsIPPI2 was detected in plastids, due to an N-terminal transit peptide which is not present in OsIPPI1. Despite the plastidial location of OsIPPI2, the expression of OsIPPI2 mRNA did not mirror the accumulation of chlorophylls or carotenoids, indicating that OsIPPI2 may be a redundant component of the MEP pathway. The detection of both OsIPPI isoforms in the ER indicates that DMAPP can be synthesized de novo in this compartment. Our work shows that the ER plays an as yet unknown role in the synthesis of MVA-derived isoprenoids, with important implications for the metabolic engineering of isoprenoid biosynthesis in higher plants.
KeywordsIsopentenyl diphosphate isomerase Endoplasmic reticulum Rice (Oryza sativa) Dimethylallyl diphosphosphate Carotenoids Gene expression
This work was supported by the National Natural Science Foundation of China (31870278); the Spanish Ministry of Economy and Competitiveness (MINECO), Spain (RTI2018-097613-B-I00; PGC2018-097655-B-I00); and in part by the European Union Framework Program DISCO (613513) “from DISCOvery to products: a next-generation pipeline for the sustainable generation of high-value plant products”, the European Cooperation in Science and Technology project EUROCAROTEN (OC-2015-1-19780), Generalitat de Catalunya Grant 2017 SGR 828 to the Agricultural Biotechnology and Bioeconomy Unit (ABBU), and the International Science and Technology Cooperation Project 20190201013JC (from Jilin Provincial Science and Technology Department, China).
Author contribution statement
CZ conceived and designed the research. XJ, CB, LG, VM, MD, XN, YS, LS, TC, PDF, and CZ conducted the experiments. XJ, CB, LG, VM, MD, XN, YS, LS, TC, PDF, PC, and CZ analyzed the data. XJ, PC, and CZ wrote the manuscript. All authors read and approved the manuscript.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
- Davies BH (1976) Carotenoids. Chemistry and Biochemistry of Plant Pigments. Academic, London, pp 38–366Google Scholar
- Guirimand G, Guihur A, Phillips MA, Oudin A, Glevarec G, Melin C, Papon N, Clastre M, St-Pierre B, Rodriguez-Concepcion M, Burlat V, Courdavault V (2012) A single gene encodes isopentenyl diphosphate isomerase isoforms targeted to plastids, mitochondria and peroxisomes in Catharanthus roseus. Plant Mol Biol 79:443–459CrossRefGoogle Scholar
- Jin X, Bai C, Bassie L, Nogareda C, Romagosa I, Twyman RM, Christou P, Zhu C (2018) ZmPBF and ZmGAMYB transcription factors independently transactivate the promoter of the maize (Zea mays) β-carotene hydroxylase 2 gene. New Phytol 11:1–14Google Scholar
- Sapir-Mir M, Mett A, Belausov E, Tal-Meshulam S, Frydman A, Gidoni D, Eyal Y (2008) Peroxisomal localization of Arabidopsis isopentenyl diphosphate isomerases suggests that part of the plant isoprenoid mevalonic acid pathway is compartmentalized to peroxisomes. Plant Physiol 148:1219–1228CrossRefGoogle Scholar
- Stamellos KD, Shackelford JE, Shechter I, Jiang G, Conrad D, Keller GA, Krisans SK (1993) Subcellular localization of squalene synthase in rat hepatic cells. J Biol Chem 268:12818–12824Google Scholar
- Zhu C, Sanahuja G, Yuan D, Farre G, Arjo G, Berman J, Zorrilla-Lopez U, Banakar R, Bai C, Perez-Massot E, Bassie L, Capell T, Christou P (2013) Biofortification of plants with altered antioxidant content and composition: genetic engineering strategies. Plant Biotechnol J 11:129–141CrossRefGoogle Scholar