Characterization and Genetic Mapping of White-Spotted Leaf (wspl) Mutant in Rice

Spotted leaf mutants which produce necrotic lesions spontaneously are important sources to study programmed cell death in plant defense responses. A novel white-spotted leaf (wspl) mutant was induced from Ilpum, Korean japonica rice cultivar by the treatment of ethyl methane sulfonate (EMS). The phenotype of wspl mutant differed from that of other spotted leaf mutants in that not only brown spots but also white lesion mimic spots were observed on the tip of the leaves from the vegetative stage. Strong nitro blue tetrazolium (NBT) and 3, 3ʹ-diaminobenzidine (DAB) staining were observed on the older leaf of wspl mutant in microscopic reactive oxygen species (ROS) assay, and the chlorophyll content of wspl mutant maintained longer than wild-type in the old leaves. Genetic analysis revealed that the wspl mutant trait was controlled by a single recessive gene and the locus of wspl gene was mapped on the long arm of chromosome 5 between the flanking markers S05100 and S05112 (4.1 Mb). Through the combination of the genetic mapping and SNP analysis, two candidate genes for white-spotted leaf were identified in the genic region. A novel phenotype of white-spotted leaf mutant has not yet been reported, thus further study of the wspl mutant will contribute to understanding of the molecular mechanisms involved in lesion mimic phenotype in rice.