A Single Amino Acid Substitution in MIL1 Leads to Activation of Programmed Cell Death and Defense Responses in Rice.

Lesion mimic mutants are an ideal model system for elucidating the molecular mechanisms of programmed cell death and defense responses in rice. In this study, we identified a lesion mimic mutant termed (). The exhibited lesions on the leaves during development, and the chloroplasts of leaves were disrupted. Reactive oxygen species were found to accumulate in leaves. Cell death and DNA fragmentation were observed in leaves, indicating that the cells in the spots of leaves experienced programmed cell death. Most agronomic traits decreased in , suggesting that the growth retardation in caused reduced per-plant grain yield. However, the mutation of activated the expression of pathogen response genes and enhanced resistance to bacterial blight. The gene was cloned using the positional cloning approach. A missense mutation 751 bp downstream of ATG was found in . The defects of were able to be rescued by delivering a wild-type gene into . encoded hydroperoxide lyase 3 (OsHPL3), and the expression of was induced via hormone and abiotic stresses. Our findings provide insights into the roles of MIL1 in regulating programmed cell death, development, yield, and defense responses in rice.