Rice Research Institute, Sichuan Agricultural University, Chengdu, China.
Institute of Crop Germplasm Resources, Guizhou Academy of Agricultural Sciences, Guiyang, China.
Plant Cell Physiol. 2018 Sep 1;59(9):1905-1917. doi: 10.1093/pcp/pcy108.
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 the cytosol cannot efficiently compensate for the deficiency of the MEP pathway in rice chloroplasts. Furthermore, real-time quantitative reverse transcription-PCR suggested that this functional defect in OsIspE affected the expression of not only other MEP pathway genes but also that of MVA pathway genes, photosynthetic genes and mitochondrial genes.
植物异戊烯基是依赖于两个独立的途径，胞质甲羟戊酸（MVA）途径和质体甲基赤藓醇磷酸（MEP）途径。IspE 是 MEP 途径中已知的七种酶之一。目前，在水稻中尚未鉴定出 IspE 基因。此外，尚未报道由于影响 MEP 途径的基因突变而导致的黄化突变体。在这项研究中，我们分离了水稻中的一个绿色可逆转的黄叶突变体 gry340。该突变体表现出光合色素水平降低，以及叶绿体和线粒体在其黄化叶片中的发育停滞。基于图谱的克隆揭示了 gry340 突变体植物中 OsIspE（LOC_Os01g58790）的一个错义突变。OsIspE 在所有组织中均组成型表达，其编码的蛋白靶向叶绿体。此外，通过引入野生型基因，gry340 的突变表型得到挽救。因此，我们通过图谱克隆成功地在单子叶植物中鉴定了一个 IspE 基因，并证实了 gry340 的绿色可逆转的黄叶表型确实是由 IspE 基因的单个核苷酸突变引起的。此外，ispE ispF 双突变体表现出黄化致死表型，表明来自胞质溶胶的异戊烯基前体不能有效地补偿水稻叶绿体中 MEP 途径的不足。此外，实时定量逆转录 PCR 表明，OsIspE 的这种功能缺陷不仅影响 MEP 途径基因的表达，还影响 MVA 途径基因、光合基因和线粒体基因的表达。
