OsLMP1, Encoding a Deubiquitinase, Regulates the Immune Response in Rice

Abstract

Lesion mimic mutants have become an effective material for understanding plant-microbe interactions and the immune mechanism in plants. Although many mechanisms responsible for the lesion mimic phenotype have been clarified in plants, the mechanism by which lesion mimic is regulated by posttranslational modification remained largely elusive, especially in rice. In this study, a mutant with the lesion mimic phenotype was obtained and named lmp1-1. Physiological measurements and quantitative real-time PCR analysis showed that the defense response was activated in the mutants. Transcriptome analysis showed that the phenylalanine ammonia lyase (PAL) pathway was activated in the mutant, causing the accumulation of salicylic acid (SA). The results of mapping based cloning showed that OsLMP1 encodes a deubiquitinase. OsLMP1 can cleave ubiquitination precursors. Furthermore, OsLMP1 epigenetically modifies SA synthetic pathway genes by deubiquitinating H2B and regulates the immune response in rice. In summary, this study deepens our understanding of the function of OsLMP1 in the plant immune response and provides further insight into the relationship between plants and pathogenic microorganisms.

Ubiquitin-Specific Protease 2 (OsUBP2) Negatively Regulates Cell Death and Disease Resistance in Rice

“…pOsUBP2 C234S could not recover the phenotype of Osubp2 ( Figure 3 C). The Oslmp1 mutant was previously reported to have truncated OsUBP2 at amino acid 868, also resulting in the deletion of the His-box and a lack of deubiquitinating enzyme activity in vitro [ 27 ]. These findings show that the His-box and the cysteine residue at position 234 in the Cys-box are essential for OsUBP2 to function normally.…”

“…During the course of this study, Sun et al 2022 independently characterized Osubp2/Oslmp1 mutant alleles. OsUBP2/OsLMP1 was shown to epigenetically modify the SA biosynthesis pathway genes by deubiquitinating H 2 B, thereby regulating the immune response in rice [ 27 ]. They attempted to verify the interaction of OsUBP2/OsLMP1 with the H 2 B variant, but the results did not verify their interaction; therefore, they proposed that OsLMP1 and H 2 B might be connected through a new regulatory link [ 27 ].…”

“…OsUBP2/OsLMP1 was shown to epigenetically modify the SA biosynthesis pathway genes by deubiquitinating H 2 B, thereby regulating the immune response in rice [ 27 ]. They attempted to verify the interaction of OsUBP2/OsLMP1 with the H 2 B variant, but the results did not verify their interaction; therefore, they proposed that OsLMP1 and H 2 B might be connected through a new regulatory link [ 27 ]. Notably, H 2 B is a universal component of a nucleosome, and, thus, the specificity of changes in H 2 B ubiquitination only at SA biosynthetic pathway genes in the mutants further suggests that H 2 B might not be a direct target of OsUBP2.…”

“…PICI1 is targeted for degradation by blast fungal effectors, including AvrPi9 , to inhibit PTI [ 26 ]. A deubiquitinating enzyme OsLMP1 (Lesion Mimic Phenotype 1) regulates immune responses in rice through the epigenetic modification of H 2 B histones [ 27 ]. The mutation of OsLMP1 resulted in lesions on the leaves and an enhanced resistance to rice bacterial blight (caused by Xanthomonas oryzae pv.…”

“…oryzae [ Xoo ] PXO99). These mutants had elevated levels of histone H 2 B ubiquitination and histone H3-K4me2/3 methylation, which directly activated the salicylic acid (SA) biosynthesis genes OsPAL6 ( Phenylalanine Ammonia-lyase Genet 6 ) and OsPAL7 ( Phenylalanine Ammonia-lyase Genet 7 ) to improve plant disease resistance [ 27 ].…”