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Lesion mimic mutants (LMMs) are plants that spontaneously form lesions without pathogen infection or external stimulus and exhibit resistance to pathogens. Here, a rice LMM was created by ethyl methane sulfonate mutagenesis, named as hpil (hydrogen peroxide induced lesion). Diaminobenzidine and trypan blue staining showed that large amounts of H2O2 were produced and cell death was occurred at and around the parts of lesion mimic in the rice leaves. The phenotype of hpil is controlled by a single recessive gene, localized at a 2 Mb interval on chromosome 2. The data suggested that hpil is a novel LMM with enhanced bacterial and fungal disease resistance, and multiple pathogenesis-related proteins (PRs) were up-regulated. The proteomes of leaves at three positions (different degrees of lesion mimic severity) were characterized in hpil compared with its wild type plant. Differentially expressed proteins were detected by two dimensional difference gel electrophoresis and 274 proteins were identified by MALDI TOF/TOF™. These proteins were related to metabolic process, cellular process and response to stimulus, with mostly down-regulated in hpil leaves. Many of these proteins were related to the Calvin cycle, photosynthetic electron transport chain, glycolysis/gluconeogenesis and phosphonates pathways. Some resistance-related proteins including 14-3-3 proteins, OsPR10 and antioxidases such as peroxidase, superoxide dismutase and ascorbate peroxidase were up-regulated in leaves with lesion mimic. These results provide the foundation for cloning of the target gene and shed light on the mechanism involved in autoimmunity of rice.

Oryza meyeriana is a wild species of rice with high resistance to Xanthomonas oryzae pv. oryzae (Xoo), but the detailed resistance mechanism is unclear. Ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) activase (RCA) is an important enzyme that regulates photosynthesis by activating Rubisco. We have previously reported that Xoo infection induced the relocation of RCA from the chloroplast stroma to the thylakoid membrane in O. meyeriana, but the underlying regulating mechanism and physiological significance of this association remains unknown. In this study, "H2O2 burst" with rapid and large increase in the amount of H2O2 was found to be induced by Xoo invasion in the leaves of O.meyeriana. 3, 3-diaminobenzidine (DAB) and oxidative 2, 7-Dichlorodi-hydrofluorescein diacetate (H2DCFDA) staining experiments both showed that H2O2 was generated in the chloroplast of O.meyeriana, and that this H2O2 generation as well as Xoo resistance of the wild rice were dramatically dependent on light. H2O2, methyl viologen with light, and the xanthine-xanthine oxidase system all induced RCA to associate with the thylakoid membrane in vitro, which showed that H2O2 could induce the relocation of RCA. In vitro experiments also showed that H2O2 induced changes in both the RCA and thylakoid membrane that were required for them to associate and that this association only occurred in O. meyeriana and not in the susceptible cultivated rice. These results suggest that the association of RCA with the thylakoid membrane helps to protect the thylakoid membrane against oxidative damage from H2O2. Therefore, in addition to its universal function of activating Rubisco, RCA appears to play a novel role in the resistance of O. meyeriana to Xoo. [ABSTRACT FROM AUTHOR]

Oryza meyeriana is a wild species of rice with high resistance to Xanthomonas oryzae pv. oryzae (Xoo), but the detailed resistance mechanism is unclear. Ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) activase (RCA) is an important enzyme that regulates photosynthesis by activating Rubisco. We have previously reported that Xoo infection induced the relocation of RCA from the chloroplast stroma to the thylakoid membrane in O. meyeriana, but the underlying regulating mechanism and physiological significance of this association remains unknown. In this study, "H 2 O 2 burst" with rapid and large increase in the amount of H 2 O 2 was found to be induced by Xoo invasion in the leaves of O. meyeriana. 3, 3-diaminobenzidine (DAB) and oxidative 2, 7-Dichlorodi-hydrofluorescein diacetate (H 2 DCFDA) staining experiments both showed that H 2 O 2 was generated in the chloroplast of O. meyeriana, and that this H 2 O 2 generation as well as Xoo resistance of the wild rice were dramatically dependent on light. H 2 O 2 , methyl viologen with light, and the xanthine-xanthine oxidase system all induced RCA to associate with the thylakoid membrane in vitro, which showed that H 2 O 2 could induce the relocation of RCA. In vitro experiments also showed that H 2 O 2 induced changes in both the RCA and thylakoid membrane that were required for them to associate and that this association only occurred in O. meyeriana and not in the susceptible cultivated rice. These results suggest that the association of RCA with the thylakoid membrane helps to protect the thylakoid membrane against oxidative damage from H 2 O 2 . Therefore, in addition to its universal function of activating Rubisco, RCA appears to play a novel role in the resistance of O. meyeriana to Xoo., Competing Interests: The authors declare no conflict of interest.