Mutation in Mg-Protoporphyrin IX Monomethyl Ester Cyclase Causes Yellow and Spotted Leaf Phenotype in Rice

Mg-protoporphyrin IX monomethyl ester cyclase (MPEC) plays an essential role in chlorophyll biosynthesis. Further study on the key enzyme will provide us more comprehensive understanding about its function. In the present study, we identified a yellow and spotted leaf 1 (ysl1) mutant in rice exhibiting a yellow-green leaf phenotype throughout the whole developmental stage and a spotted leaf phenotype at seedling and tillering stages. Genetic analysis indicated that a single recessive gene was responsible for the phenotype of ysl1 mutant. Map-based cloning showed that the mutation site was located at the region of 105.4-kb between RM572 and L3 on the short arm of chromosome 1. Sequence analysis revealed that a point mutation (C-to-T) happened in the coding region of candidate gene YSL1 (LOC_Os01g17170) which caused an amino acid change in MPEC. YSL1 was expressed mainly in photosynthetic tissues and organs, and its encoded protein was transported into the chloroplast with a signal peptide. The phenotype of ysl1 returned to normal phenotype of wild type after introducing the wild-type YSL1 gene. Based on the evidence from different levels, we confirmed that the phenotype of ysl1 was caused by a single nucleotide substitution of YSL1 which is allelic to YGL8, OsCRD1, and YL-1, and demonstrated the spotted leaf at seedling and tillering stages as a novel phenotype of the MPEC mutants in rice.