CS3, a Ycf54 domain-containing protein, affects chlorophyll biosynthesis in rice (Oryza sativa L.)

Chlorophyll plays a vital role in harvesting light and turning it into chemical energy. In this study, we isolated and characterized a chlorophyll-deficient mutant, which we named cs3 (chlorotic seedling 3). The cs3 mutant seedlings exhibit a yellowish phenotype at germination, and they do not survive at the seedling stage. In addition, brown necrotic spots appear on the surface of the leaves and leaf sheaths during development. DAB staining and H₂O₂ content measurement showed that there was excessive H₂O₂ accumulation in the cs3 mutant leaf. Accompanying the chlorophyll deficiency, the chloroplasts in cs3 leaf cells were abnormal. Using a map-based cloning strategy, we mapped the CS3 gene, which encodes a Ycf54 domain-containing protein, to a locus on chromosome 3. CS3 is mainly expressed in green tissues and the S136 F would influence CS3 interacting with YGL8 and its chloroplast localization. qRT-PCR analysis revealed the changes in the expression of genes involved in chlorophyll biosynthesis and degradation, chloroplast development, senescence, and photosynthesis in the cs3 mutant. In addition, our study also supports the notion that the mutation in the CS3/Ycf54 gene arrests chlorophyll biosynthesis by negatively affecting the activity of magnesium protoporphyrin IX monomethylester cyclase (MgPME-cyclase).