A Single Nucleotide Mutation of the IspE Gene Participating in the MEP Pathway for Isoprenoid Biosynthesis Causes a Green Revertible Yellow Leaf Phenotype in Rice
Plant isoprenoids are dependent on two independent pathways, the cytosolic mevalonate (MVA) pathway and the plastidic methylerythritol phosphate (MEP) pathway. IspE is one of seven known enzymes in the MEP pathway. Currently, no IspE gene has been identified in rice. In addition, no virescent mutants have been reported to result from a gene mutation affecting the MEP pathway. In this study, we isolated a green revertible yellow leaf mutant gry340 in rice. The mutant exhibited a reduced level of photosynthetic pigments, and an arrested development of chloroplasts and mitochondria in its yellow leaves. Map based cloning revealed a missense mutation in OsIspE (LOC_Os01g58790) in gry340 mutant plants. OsIspE is constitutively expressed in all tissues, and its encoded protein is targeted to the chloroplast. Further, the mutant phenotype of gry340 was rescued by introduction of the wild type gene. Therefore, we have successfully identified an IspE gene in monocotyledons via map based cloning, and confirmed that the green revertible yellow leaf phenotype of gry340 does result from a single nucleotide mutation in the IspE gene. In addition, the ispE ispF double mutant displayed an etiolation lethal phenotype, indicating that the isoprenoid precursors from cytosol cannot efficiently compensate for the deficiency of the MEP pathway in rice chloroplasts. Furthermore, real time quantitative RT PCR suggested that this functional defect in OsIspE not only affected the expression of other MEP pathway genes, but that of MVA pathway genes, photosynthetic genes, and mitochondrial genes.
Plant cell physiology