We identified a new rice lesion mimic mutant lmm24 from a mutant pool of indica rice cultivar "ZhongHui8015". The LMM24 gene was identified by MutMap, and LMM24 was confirmed as a receptor-like cytoplasmic kinase 109 by amino acid sequence analysis. The lmm24 mutant displayed dark brown lesions in leaves and growth retardation that were not observed in wild-type ZH8015. The results of histochemical staining and TUNEL assays showed enhanced ROS accumulation and cell death in lmm24. Chloroplast degradation was observed in lmm24leaves, with decreased expression of photosynthesis-related genes and increased expression of the senescence-induced STAYGREEN(SGR) gene and other senescence-associated genes. Furthermore, lmm24 exhibited enhanced resistance to rice blast fungus Magnaporthe oryzae (M. oryzae) and up-regulation of defense response genes. Our data demonstrate that LMM24 regulates cell death and defense responses in rice.
Figure 1: Phenotypic analyses of lmm24. (A) Comparison of growing situation ZH8015 and lmm24 at seedling stage (15 days post-sowing (dps)). (B) lmm24 plant at tillering stage (50 dps) display dark brown lesions. (C) Lesion mimic phenotype in lmm24 and clean leaf blade in ZH8015. (D) Determination of whether the lmm24 phenotype was light dependent. The area covered with aluminum was indicated by red rectangle frame. (E) ZH8015 and lmm24 plants at harvest period (F) Grain width observation of lmm24 and ZH8015. (G) Grain length observation of lmm24 and ZH8015. Scale bar: 2 cm in (A,C), 1 cm in (D,F,G), 10 cm in (B,E).