The rice (Oryza sativa L.) LESION MIMIC RESEMBLING, which encodes an AAA-type ATPase, is implicated in defense response

Abstract

Lesion mimic mutants (LMMs) provide a useful tool to study defense-related programmed cell death (PCD) in plants. Although a number of LMMs have been identified in multiple species, most of the candidate genes are yet to be isolated. Here, we report the identification and characterization of a novel rice (Oryza sativa L.) lesion mimic resembling (lmr) mutant, and cloning of the corresponding LMR gene. The LMR locus was initially delineated to 1.2 Mb region on chromosome 6, which was further narrowed down to 155-kb using insertions/deletions (INDELs) and cleavage amplified polymorphic sequence markers developed in this study. We sequenced the open reading frames predicted within the candidate genomic region, and identified a G–A base substitution causing a premature translation termination in a gene that encodes an ATPase associated with various cellular activities type (AAA-type) protein. RNA interference transgenic lines with reduced LMR transcripts exhibited the lesion mimic phenotype similar to that of lmr plants. Furthermore, expression of the wild-type LMR in the mutant background complemented the lesion phenotype, confirming that the mutation identified in LMR is responsible for the mutant phenotype. The pathogenesis-related (PR) genes PBZ1 and PR1 were induced in lmr, which also showed enhanced resistance to rice blast (Magnaportheoryzae) and bacterial blight (Xanthomonas oryzae pv. oryzae), suggesting LMR is a negative regulator of cell death in rice. The identification of lmr and cloning of the corresponding LMR gene provide an additional resource for the study of PCD in plants.