Lesion mimic mutant 8 balances disease resistance and growth in rice.

Lesion-mimic mutants (LMM) spontaneously produce necrotic spots, a process not affected by environmental stress or pathogen infection. In this study, we identified a LMM, () in rice (). The mutant produces brown and off-white lesions on its leaves during the second- and third-leaf stages. The lesion mimic phenotype of the mutant was enhanced by light. At the mature stage, mutant are shorter and exhibit inferior agronomic traits than the wild type. Contents of photosynthetic pigments and chloroplast fluorescence were significantly reduced in leaves, along with increased production of reactive oxygen species and programmed cell death compared to the wild type. The mutated gene was identified as () by map-based cloning. A point mutation occurred in , causing a Leu to Arg mutation of the 146th amino acid of LMM8. It is an allele of , encoding a protoporphyrinogen IX oxidase (PPOX) located in chloroplasts and involved in the biosynthesis of tetrapyrrole in chloroplasts. The mutant showed enhanced resistance and broad-spectrum resistance. Together, our results demonstrate the importance of rice LMM8 protein in defense responses and plant growth in rice, and provides theoretical support for resistance breeding to improve rice yield.