Lesion Mimic Mutant: An Ideal Genetic Material for Deciphering the Balance Between Plant Immunity and Growth

Lesion mimic mutants (LMMs) form hypersensitive response (HR)-like lesions, a form of programmed cell death (PCD), in the absence of pathogens, that often confer durable and broad-spectrum disease resistance, representing a potential source for breeding resistance. However, most LMM plants have significant growth retardation including cell death, leaf senescence, damaged chloroplast structure, decreased chlorophyll contents, and undesirable agronomic traits. Therefore, LMMs represent ideal genetic materials to decipher interactions between defense signaling and programmed cell death, and growth. Many LMMs have been identified in rice, and at least 61 genes have been cloned and functionally confirmed. LMM genes are reported to participate in various regulation pathways, including gene transcription and protein translation, ubiquitin-proteasome pathway, protein phosphorylation, vesicle trafficking, metabolic pathways, and phytohormone signaling, highlighting the complexity of regulatory mechanisms. This review discusses recent progress on characteristics of rice LMM and mechanisms of LMM gene regulation, and suggests directions for future theoretical research and the potential use of LMMs in rice breeding.