Wang Xuexia, Huang Rongfeng, Quan Ruidang
Biotechnology Research Institute, Chinese Academy of Agricultural Sciences, Beijing, China.
National Key Facility of Crop Gene Resources and Genetic Improvement, Beijing, China.
PLoS One. 2017 Jan 27;12(1):e0171118. doi: 10.1371/journal.pone.0171118. eCollection 2017.
In photosynthesis, the pigments chlorophyll a/b absorb light energy to convert to chemical energy in chloroplasts. Though most enzymes of chlorophyll biosynthesis from glutamyl-tRNA to chlorophyll a/b have been identified, the exact composition and regulation of the multimeric enzyme Mg-protoporphyrin IX monomethyl ester cyclase (MPEC) is largely unknown. In this study, we isolated a rice pale-green leaf mutant m167 with yellow-green leaf phenotype across the whole lifespan. Chlorophyll content decreases 43-51% and the granal stacks of chloroplasts becomes thinner in m167. Chlorophyll fluorescence parameters, including Fv/Fm (the maximum quantum efficiency of PSII) and quantum yield of PSII (Y(II)), were lower in m167 than those in wild type plants (WT), and photosynthesis rate decreases 40% in leaves of m167 mutant compared with WT plants, which lead to yield reduction in m167. Genetic analysis revealed that yellow-green leaf phenotype of m167 is controlled by a single recessive genetic locus. By positional cloning, a single mutated locus, G286A (Alanine 96 to Threonine in protein), was found in the coding sequence of LOC_Os01g17170 (Rice Copper Response Defect 1, OsCRD1), encoding a putative subunit of MPEC. Expression profile analysis demonstrated that OsCRD1 is mainly expressed in green tissues of rice. Sequence alignment analysis of CRD1 indicated that Alanine 96 is very conserved in all green plants and photosynthetic bacteria. OsCRD1 protein mainly locates in chloroplast and the point mutation A96T in OsCRD1 does not change its location. Therefore, Alanine96 of OsCRD1 might be fundamental for MPEC activity, mutation of which leads to deficiency in chlorophyll biosynthesis and chloroplast development and decreases photosynthetic capacity in rice.
在光合作用中，叶绿素a/b色素吸收光能并在叶绿体中转化为化学能。尽管从谷氨酰-tRNA到叶绿素a/b的叶绿素生物合成的大多数酶已被鉴定，但多聚酶镁原卟啉IX单甲酯环化酶（MPEC）的确切组成和调控在很大程度上尚不清楚。在本研究中，我们分离出一个水稻淡绿叶突变体m167，其在整个生命周期中都表现出黄绿色叶片表型。m167中叶绿素含量降低43%-51%，叶绿体的基粒垛变得更薄。叶绿素荧光参数，包括Fv/Fm（PSII的最大量子效率）和PSII的量子产率（Y(II)），在m167中低于野生型植株（WT），并且与WT植株相比，m167突变体叶片的光合速率降低40%，这导致m167产量降低。遗传分析表明，m167的黄绿色叶片表型由单个隐性遗传位点控制。通过图位克隆，在LOC_Os01g17170（水稻铜响应缺陷1，OsCRD1）的编码序列中发现了一个单一突变位点G286A（蛋白质中第96位丙氨酸突变为苏氨酸），该基因编码MPEC的一个假定亚基。表达谱分析表明，OsCRD1主要在水稻的绿色组织中表达。CRD1的序列比对分析表明，第96位丙氨酸在所有绿色植物和光合细菌中都非常保守。OsCRD1蛋白主要定位在叶绿体中，并且OsCRD1中的点突变A96T不会改变其定位。因此，OsCRD1的第96位丙氨酸可能对MPEC活性至关重要，其突变导致水稻叶绿素生物合成和叶绿体发育缺陷，并降低光合能力。
