Disruption of EARLY LESION LEAF 1, encoding a cytochrome P450 monooxygenase, induces ROS accumulation and cell death in rice.

LMMs (lesion-mimic mutants) provide a valuable tool to reveal the molecular mechanisms determining programmed cell death in plants. Despite numerous of research, the mechanisms behind PCD and the formation of lesions in various LMMs are still being elucidated. Here, we identified a rice LMM, early lesion leaf 1 (ell1), cloned the causal gene by map-based cloning, and verified this by complementation. ELL1 encodes a cytochrome P450 monooxygenase, and the ELL1 protein was located in the endoplasmic reticulum (ER). The ell1 mutant exhibited decreased chlorophyll contents, serious chloroplast degradation, up-regulated expression of chloroplast degradation-related genes, and attenuated photosynthetic protein activity, indicating that ELL1 is involved in chloroplast development. RNA-seq analysis showed that genes related to oxygen binding were differentially expressed in ell1 and wild-type plants; histochemical and paraffin sectioning results displayed that hydrogen peroxide (H2 O2 ) and callose accumulated in the ell1 leaves, and the cell structure around the lesion was severely damaged, which indicated that reactive oxygen species (ROS) accumulated and cell death occurred in the mutant. TUNEL and comet experiments revealed that severe DNA degradation and abnormal PCD occurred in the mutant, which implied that excessive ROS accumulation may induce DNA damage and ROS-mediated cell death in the ell1 mutant. Additionally, lesion initiation in the ell1 mutant was light dependent and temperature sensitive. Our findings revealed that ELL1 affects chloroplast development or function, and that loss of ELL1 function induces ROS accumulation and lesion formation in rice.