White-Green Leaf Gene Encoding Protochlorophyllide Oxidoreductase B Is Involved in Chlorophyll Synthesis of Rice

A white-green leaf (wgl1) mutant, derived from Nipponbare (NIP) (Oryza sativa L. ssp. japonica) treated with ethyl methanesulfonate, exhibited white-green leaf variegation and brown necrotic lesions during old leaf elongation. However, the wgl1 mutant gradually changed in color from white-green to light green at the later stages of development in field-grown plants. Pigment investigation showed that the change in leaf color in wgl1 mutant is associated with chlorophyll (Chl) and carotenoid content reduction. Electron microscopic analysis of wgl1 chloroplasts revealed a decrease in the number of chloroplasts and loss of grana stacks. In addition, the prolamellar bodies of wgl1etioplasts were smaller than that of NIP etioplasts with concentric-rings stromal thylakoids in 7-d-old darkness-grown seedlings. As a result, chloroplast development was impaired. Genetic analysis results showed that the wgl1 mutant phenotype was caused by recessive mutations in a single nuclear gene. Map-based cloning and complementation tests revealed that WGL1, located on chromosome 10, encodes OsPOR B (Os10 g35370), one of two isoforms of nicotinamide adenine dinucleotide 2'-phosphate reduced tetrasodium salt: protochlorophyllide oxidoreductase (POR). Real-time polymerase chain reaction analysis and beta-Glucuronidase reporter results showed that the highest expression levels were observed in flag leaves, whereas expression in the root was almost undetected. These results indicate that WGL1 is involved in Chl biosynthesis and chloroplast development in rice.