| Summary: | Lesion mimic mutants (LMMs) are great materials for studying programmed cell death and immune mechanisms in plants. Various mechanisms are involved in the phenotypes of different LMMs, but few studies have explored the mechanisms linking deubiquitination and LMMs in rice (<i>Oryza sativa</i>). Here, we identified a rice LMM, <i>rust spots rice</i> (<i>rsr1</i>), resulting from the mutation of a single recessive gene. This LMM has spontaneous reddish-brown spots on its leaves, and displays enhanced resistance to both fungal leaf blast (caused by <i>Magnaporthe oryzae</i>) and bacterial blight (caused by <i>Xanthomonas oryzae</i> pv. <i>oryzae</i>). Map-based cloning showed that the mutated gene in <i>rsr1</i> encodes a Ubiquitin-Specific Protease 2 (OsUBP2). The mutation of <i>OsUBP2</i> was shown to result in reactive oxygen species (ROS) accumulation, chloroplast structural defects, and programmed cell death, while the overexpression of <i>OsUBP2</i> weakened rice resistance to leaf blast. OsUBP2 is therefore a negative regulator of immune processes and ROS production. OsUBP2 has deubiquitinating enzyme activity in vitro, and the enzyme active site includes a cysteine at the 234th residue. The ubiquitinated proteomics data of <i>rsr1</i> and WT provide some possible target protein candidates for OsUBP2.
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