Phenotypic and Genotypic Analysis of Rice Lesion Mimic Mutants

Lesion mimic mutant (LMM) plants display spontaneous necrotic lesions on their leaves without any pathogenic infection. Specific rice LMMs designated as spotted leaf (spl) including spl1, spl3, spl4, spl5 and spl6 are genetically known as lesion resembling disease (lrd) mutant. The inheritance patterns in the $F_1$ and $F_2$ progenies of these mutants are controlled by recessive genetic factors. Lesion development in the rice LMMs were controlled by both development stages and environmental factors. The rice LMMs exhibited higher numbers of spots under $45^{\circ}C$ temperature than those under $30^{\circ}C$. Contents of chlorophyll were drastically reduced at 60 days old LMM leaves when the spot formation was severe. The levels of endogenous hydrogen peroxide were highest at 45 days old mutants but reduced at 60 days old. Transcription levels of stress related genes including thioredoxin peroxidase and protein disulfide isomerase were reduced in spotted leaves than those of non spotted leaves. It could be suggested that scavenging system against reactive oxygen species induced by either stresses or innate metabolisms may not work properly in the rice LMMs. As these rice LMMs autonomously expressed clear lesions of lrd phenotype without pathogen infection, it could be useful to understand stresses responses in plants.