Characterization, Genetic Analysis And Gene Mapping Of Two Spotted Leaf Mutants In Rice

Spotted-leaf mutants are ideal resources for understanding of programmed cell death and disease resistance. We identified two rice spotted-leaf mutants hm197 and hm83 from mutagenesis of an elite indica cultivar IR64. In order to study the mechanism involved in the initation of lesions, we carried out studies on their agronomic traits, physiological and biochemical characteristics, evaluation of disease resistance to Xanthomonus oryzae pv. oryzae, genetic control of the lesions and mapping analysis of the mutations. Major results are as follows:1 A stable inherited rice spotted-leaf mutant hm197 was isolated from a diepoxybutane-induced IR64 mutant bank. Under summer natural conditions, brown lesions were first observed on the tips of the mutant leaves 10 weeks after sowing, and spread gradually downward to cover the whole leaf blades. Agronomic traits including the plant height, seed-setting rate and 1000-grain weight were also decreased significantly in hm197 than those of the wild type IR64. The initiation of brown lesions in hm197 was induced by natural sun light. In addition, the photosynthetic pigment contents and net photosynthetic rate in the mutant were significantly lower than those of the wild type IR64. Histochemical analysis showed that H2O2 and O2- accumulation were presented in and around the lesions in hm197. Furthermore, senescence-related parameters were also significantly changed in the mutant while disease resistance to bacterial blight pathogens was largely enhanced in the mutant in contrast to the wild type IR64. Genetic analysis indicated that the mutant trait was controlled by a novel single recessive nuclear gene, tentatively termed splhm197, in the long arm of chromosome 4. The data and populations obtained in the present study would facilitate the isolation and functional analysis of splhm197.2 A stable inherited rice spotted-leaf mutant hm83 was isolated from an EMS-induced IR64 mutant bank. Under natural conditions, reddish brown lesions were first observed on the mutant leaves around the mid-veins 12 weeks after sowing, and then cover the whole leaf blades. Agronomic traits including the plant height was decreased significantly in hm83, but seed-setting rate and 1000-grain weight did not have difference compared with the wild type IR64. In addition, the photosynthetic pigment contents and net photosynthetic rate in the mutant were significantly lower than those of the wild type IR64. Histochemical analysis showed that H2O2 and O2- accumulation were presented in and around the lesions in hm83. Furthermore, senescence-related parameters were also significantly changed in the mutant while disease resistance to bacterial blight pathogens was largely enhanced in the mutant in contrast to the wild type IR64. What’s more, the lesion mimic phenotype was highly associated with resistance to Xathomonus oryzae pv. oryzae. Genetic analysis indicated that the mutant trait was controlled by a novel single recessive nuclear gene, tentatively termed splhm83, in the long arm of chromosome 1.