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

Abstract

Lesion-mimic mutants (LMMs) provide a valuable tool to reveal the molecular mechanisms determining programmed cell death (PCD) in plants. Despite intensive research, the mechanisms behind PCD and the formation of lesions in various LMMs still remain to be elucidated. Here, we identified a rice (Oryza sativa) 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. The ell1 mutant exhibited decreased chlorophyll contents, serious chloroplast degradation, upregulated expression of chloroplast degradation-related genes, and attenuated photosynthetic protein activity, indicating that ELL1 is involved in chloroplast development. RNA sequencing analysis showed that genes related to oxygen binding were differentially expressed in ell1 and wild-type plants; histochemistry and paraffin sectioning results indicated that hydrogen peroxide (H 2 O 2) and callose accumulated in the ell1 leaves, and the cell structure around the lesions was severely damaged, which indicated that reactive oxygen species (ROS) accumulated and cell death occurred in the mutant. TUNEL staining and comet experiments revealed that severe DNA degradation and abnormal PCD occurred in the ell1 mutants, which implied that excessive ROS accumulation may induce DNA damage and ROS-mediated cell death in the 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.

Altered Expression of OsAAP3 Influences Rice Lesion Mimic and Leaf Senescence by Regulating Arginine Transport and Nitric Oxide Pathway

“…In the present study, Pro accumulated in the OsAAP3 OE lines, but decreased in the Ri lines ( Figure S3 ), indicating that Pro may be involved in the ROS pathway. As the MDA content indirectly reflects the degree of cellular damage [ 26 ], our results also showed that the MDA content in the OsAAP3 OE lines was significantly increased ( Figure 2 D), as observed for the ell1 mutant with ROS accumulation and lesion formation [ 27 ].…”

“…The staining results indicated that the OsAAP3 OE lines might give rise to the production of cell death in rice leaf. In recent years, there are many reports about the mechanism of ROS mediated cell death [ 2 , 27 , 33 ]. For example, the mutation in ELL1 disrupted the structure of chloroplast, then further caused accumulation of ROS, which ultimately triggered cell death of rice leaf [ 27 ].…”

Mutation Types of CYP71P1 Cause Different Phenotypes of Mosaic Spot Lesion and Premature Leaf Senescence in Rice

“…Thus, the single base substitution in the LOC_Os12g16720 locus confers the mosaic spot lesion phenotype of both mutants msl-1 and msl-2. This conclusion has been supported by the recently published research on ell1 (early lesion leaf 1) and sl-MH-1, which are LMM mutants from the japonica rice variety Wuyunjing7 and indica rice line Minghui 86 (MH86), respectively, at the LOC_Os12g16720 locus (Tian et al, 2020;Cui et al, 2021).…”

“…It has been shown that serotonin is involved in the immune response of plants, and exogenous applied serotonin enhances resistance to Magnaporthe grisea (M. grisea) in the sl mutant (Fujiwara et al, 2010). In addition, the serotonin is acknowledged to be a kind of strong antioxidant compounds by scavenging ROS (Huether et al, 1997), which is in agreement with excessive ROS accumulation in the sl mutants (Cui et al, 2021; Figure 3). Excessive ROS accumulation triggers off programmed cell death (PCD)-mediated cell apoptosis, causing the lesion formation in rice (Cui et al, 2021).…”

“…The mutant msl-2 has a G-to-A single-base alteration, leading to premature termination of the protein translation ( Figure 6C); while msl-1 was mutated from T to C at 218 nucleotide position (T218C) in the first exon of SL, which cause an amino acid change from isoleucine to proline (Leu73Pro) ( Figure 6B). Recently, Cui et al (2021) have cloned another allelic mutant (ell1) of SL, which has a single base mutation at 275 nucleotide position (C275A) in the first exon and changed an amino acid from alanine to aspartic acid at the 92nd position of protein sequence (Figure 6A). Interestingly, additional mutants at the SL locus have been generated from the indica rice line MH86 by tissue culture (sl-MH-1) and by 60 Co ∼ γ-ray radiation (sl-MH-2 and sl-MH-3), respectively (Tian et al, 2020).…”