RESUMO
Plant plasma membrane-localized receptors recognize microbe-associated molecular patterns (MAMPs) and activate immune responses via various signaling pathways. Receptor-like cytoplasmic kinases (RLCKs) are considered key signaling factors in plant immunity. BROAD-SPECTRUM RESISTANCE 1 (BSR1), a rice RLCK, plays a significant role in disease resistance. Overexpression of BSR1 confers strong resistance against fungal and bacterial pathogens. Our recent study revealed that MAMP-triggered immune responses are mediated by BSR1 in wild-type rice and are hyperactivated in BSR1-overexpressing rice. It was suggested that hyperactivated immune responses were responsible for the enhancement of broad-spectrum disease resistance; however, this remained to be experimentally validated. In this study, we verified the above hypothesis by disrupting the MAMP-recognition system in BSR1-overexpressing rice. To this end, we knocked out OsCERK1, which encodes a well-characterized MAMP-receptor-like protein kinase. In the background of BSR1 overaccumulation, the knockout of OsCERK1 nearly abolished the enhancement of blast resistance. This finding indicates that overexpressed BSR1-mediated enhancement of disease resistance depends on the MAMP-triggered immune system, corroborating our previously suggested model.
Assuntos
Ascomicetos/genética , Oryza/genética , Doenças das Plantas/genética , Imunidade Vegetal/genética , Proteínas de Plantas/genética , Proteínas Serina-Treonina Quinases/genética , Receptores de Reconhecimento de Padrão/genética , Ascomicetos/crescimento & desenvolvimento , Ascomicetos/patogenicidade , Sequência de Bases , Resistência à Doença , Regulação da Expressão Gênica de Plantas/imunologia , Técnicas de Silenciamento de Genes , Interações Hospedeiro-Patógeno/genética , Interações Hospedeiro-Patógeno/imunologia , Oryza/imunologia , Oryza/microbiologia , Moléculas com Motivos Associados a Patógenos/química , Moléculas com Motivos Associados a Patógenos/metabolismo , Doenças das Plantas/imunologia , Proteínas de Plantas/imunologia , Plantas Geneticamente Modificadas , Proteínas Serina-Treonina Quinases/imunologia , Receptores de Reconhecimento de Padrão/deficiência , Receptores de Reconhecimento de Padrão/imunologia , Transdução de SinaisRESUMO
Plants activate their immune system through intracellular signaling pathways after perceiving microbe-associated molecular patterns (MAMPs). Receptor-like cytoplasmic kinases mediate the intracellular signaling downstream of pattern-recognition receptors. BROAD-SPECTRUM RESISTANCE 1 (BSR1), a rice (Oryza sativa) receptor-like cytoplasmic kinase subfamily-VII protein, contributes to chitin-triggered immune responses. It is valuable for agriculture because its overexpression confers strong disease resistance to fungal and bacterial pathogens. However, it remains unclear how overexpressed BSR1 reinforces plant immunity. Here we analyzed immune responses using rice suspension-cultured cells and sliced leaf blades overexpressing BSR1. BSR1 overexpression enhances MAMP-triggered production of hydrogen peroxide (H2O2) and transcriptional activation of the defense-related gene in cultured cells and leaf strips. Furthermore, the co-cultivation of leaves with conidia of the blast fungus revealed that BSR1 overexpression allowed host plants to produce detectable oxidative bursts against compatible pathogens. BSR1 was also involved in the immune responses triggered by peptidoglycan and lipopolysaccharide. Thus, we concluded that the hyperactivation of MAMP-triggered immune responses confers BSR1-mediated robust resistance to broad-spectrum pathogens.
Assuntos
Resistência à Doença , Oryza/imunologia , Oryza/metabolismo , Doenças das Plantas/imunologia , Proteínas de Plantas/metabolismo , Receptores de Reconhecimento de Padrão/metabolismo , Resistência à Doença/genética , Regulação da Expressão Gênica de Plantas , Genes de Plantas , Peróxido de Hidrogênio/metabolismo , Magnaporthe/fisiologia , Modelos Biológicos , Oryza/genética , Oryza/microbiologia , Peptidoglicano/metabolismo , Doenças das Plantas/genética , Doenças das Plantas/microbiologia , Folhas de Planta/microbiologia , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Explosão RespiratóriaRESUMO
Various viruses infect Magnaporthe oryzae (syn. Pyricularia oryzae), which is a well-studied fungus that causes rice blast disease. Most research has focused on the discovery of new viruses and the hypovirulence-associated traits conferred by them. Therefore, the diversity and prevalence of viruses in wild fungal populations have not been explored. We conducted a comprehensive screening of M. oryzae mycoviruses from various regions in Japan using double-stranded RNA (dsRNA) electrophoresis and RT-PCR assays. We detected three mycoviruses, Magnaporthe oryzae virus 2 (MoV2), Magnaporthe oryzae chrysovirus 1 (MoCV1), and Magnaporthe oryzae partitivirus 1 (MoPV1), among 127 of the 194 M. oryzae strains screened. The most prevalent virus was MoPV1 (58.8%), which often co-infected in a single fungal strain together with MoV2 or MoCV1. MoV2 and MoCV1 were found in 22.7 and 10.8% of strains, respectively, and they were usually distributed in different regions so that mixed-infection with these two mycoviruses was extremely rare. The predominance of MoPV1 in M. oryzae is supported by significant negative values from neutrality tests, which indicate that the population size of MoPV1 tends to increase. Population genetic analyses revealed high nucleotide diversity and the presence of phylogenetically diverse subpopulations among the MoV2 isolates. This was not the case for MoPV1. Furthermore, studies of a virus-cured M. oryzae strain revealed that MoV2 does not cause any abnormalities or symptoms in its host. However, a leaf sheath inoculation assay showed that its presence slightly increased the speed of mycelial growth, compared with virus-free mycelia. These results demonstrate that M. oryzae in Japan harbors diverse dsRNA mycovirus communities with wide variations in their population structures among different viruses.