RESUMO
Active oxygen species (AOS) generated in response to stimuli and during development can function as signalling molecules in eukaryotes, leading to specific downstream responses. In plants these include such diverse processes as coping with stress (for example pathogen attack, wounding and oxygen deprivation), abscisic-acid-induced guard-cell closure, and cellular development (for example root hair growth). Despite the importance of signalling via AOS in eukaryotes, little is known about the protein components operating downstream of AOS that mediate any of these processes. Here we show that expression of an Arabidopsis thaliana gene (OXI1) encoding a serine/threonine kinase is induced in response to a wide range of H2O2-generating stimuli. OXI1 kinase activity is itself also induced by H2O2 in vivo. OXI1 is required for full activation of the mitogen-activated protein kinases (MAPKs) MPK3 and MPK6 after treatment with AOS or elicitor and is necessary for at least two very different AOS-mediated processes: basal resistance to Peronospora parasitica infection, and root hair growth. Thus, OXI1 is an essential part of the signal transduction pathway linking oxidative burst signals to diverse downstream responses.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Sistema de Sinalização das MAP Quinases , Proteínas Serina-Treonina Quinases/metabolismo , Explosão Respiratória , Arabidopsis/enzimologia , Arabidopsis/genética , Arabidopsis/parasitologia , Proteínas de Arabidopsis/genética , Celulase/metabolismo , Ativação Enzimática/efeitos dos fármacos , Indução Enzimática/efeitos dos fármacos , Genes Reporter , Teste de Complementação Genética , Peróxido de Hidrogênio/metabolismo , Peróxido de Hidrogênio/farmacologia , Sistema de Sinalização das MAP Quinases/efeitos dos fármacos , Quinases de Proteína Quinase Ativadas por Mitógeno/metabolismo , Proteínas Quinases Ativadas por Mitógeno/metabolismo , Phytophthora/fisiologia , Doenças das Plantas/genética , Doenças das Plantas/parasitologia , Raízes de Plantas/enzimologia , Raízes de Plantas/crescimento & desenvolvimento , Raízes de Plantas/metabolismo , Proteínas Serina-Treonina Quinases/genética , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Espécies Reativas de Oxigênio/metabolismoRESUMO
Plants respond to biotic and abiotic stresses by inducing overlapping sets of mitogen-activated protein kinases (MAPKs) and response genes. To define the mechanisms of how different signals can activate a common signaling pathway, upstream activators of SIMK, a salt stress- and pathogen-induced alfalfa MAPK, were identified. Here, we compare the properties of SIMKK, a MAPK kinase (MAPKK) that mediates the activation of SIMK by salt stress, with those of PRKK, a distantly related novel MAPKK. Although both SIMKK and PRKK show strongest interaction with SIMK, SIMKK can activate SIMK without stimulation by upstream factors. In contrast, PRKK requires activation by an upstream activated MAPKK kinase. SIMKK mediates pathogen elicitor signaling and salt stress, but PRKK transmits only elicitor-induced MAPK activation. Of four tested MAPKs, PRKK activates three of them (SIMK, MMK3, and SAMK) upon elicitor treatment of cells. However, PRKK is unable to activate any MAPK upon salt stress. In contrast, SIMKK activates SIMK and MMK3 in response to elicitor, but it activates only SIMK upon salt stress. These data show that (1) MAPKKs function as convergence points for stress signals, (2) MAPKKs activate multiple MAPKs, and (3) signaling specificity is obtained not only through the inherent affinities of MAPKK-MAPK combinations but also through stress signal-dependent intracellular mechanisms.
Assuntos
Medicago sativa/genética , Quinases de Proteína Quinase Ativadas por Mitógeno/genética , Proteínas Quinases Ativadas por Mitógeno/genética , Proteínas de Plantas/genética , Transdução de Sinais , Sequência de Aminoácidos , Clonagem Molecular , Expressão Gênica , MAP Quinase Quinase Quinases/metabolismo , Sistema de Sinalização das MAP Quinases/efeitos dos fármacos , Medicago sativa/efeitos dos fármacos , Medicago sativa/enzimologia , Quinases de Proteína Quinase Ativadas por Mitógeno/isolamento & purificação , Quinases de Proteína Quinase Ativadas por Mitógeno/metabolismo , Proteínas Quinases Ativadas por Mitógeno/metabolismo , Dados de Sequência Molecular , Proteínas de Plantas/isolamento & purificação , Proteínas de Plantas/metabolismo , Plantas Geneticamente Modificadas , Homologia de Sequência de Aminoácidos , Cloreto de Sódio/farmacologia , TransfecçãoRESUMO
Ethylene signal transduction involves ETR1, a two-component histidine protein kinase receptor. ETR1 functions upstream of the negative regulator CTR1. The similarity of CTR1 to members of the Raf family of mitogen-activated protein kinase kinase kinases (MAPKKKs) suggested that ethylene signaling in plants involves a MAPK pathway, but no direct evidence for this has been provided. Here we show that distinct MAPKs are activated by the ethylene precursor aminocyclopropane-1-carboxylic acid (ACC) in Medicago and Arabidopsis: In Medicago, the ACC-activated MAPKs were SIMK and MMK3, while in Arabidopsis MPK6 and another MAPK were identified. Medicago SIMKK specifically mediated ACC-induced activation of SIMK and MMK3. Transgenic Arabidopsis plants overexpressing SIMKK have constitutive MPK6 activation and ethylene-induced target gene expression. SIMKK overexpressor lines resemble ctr1 mutants in showing a triple response phenotype in the absence of ACC. Whereas MPK6 was not activated by ACC in etr1 mutants, ein2 and ein3 mutants showed normal activation profiles. In contrast, ctr1 mutants showed constitutive activation of MPK6. These data indicate that a MAPK cascade is part of the ethylene signal transduction pathway in plants.