Research Article: Mutation in Mg-Protoporphyrin IX Monomethyl Ester Cyclase Decreases Photosynthesis Capacity in Rice

Date Published: January 27, 2017

Publisher: Public Library of Science

Author(s): Xuexia Wang, Rongfeng Huang, Ruidang Quan, Steven M. Theg.


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.

Partial Text

Photosynthesis is the process of converting light energy to chemical energy and is the most important source of energy on the earth [1]. Chlorophyll (Chl) molecules harvest light energy for photosynthesis, so Chls are key cofactors for the photosynthetic apparatus [2].

Chlorophylls are essential for photosynthesis and plant growth. Chlorophyll biosynthesis is a highly coordinated process that is executed via a series of cooperative reactions catalyzed by numerous enzymes. However, only several genes have been studied in rice. In this study, we characterized a yellow-green leaf rice mutant m167. By map-based cloning, we cloned the mutation gene OsCRD1, encoding a putative subunit of MPEC, the most enigmatic enzyme in chlorophyll biosynthesis.




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