RESUMEN
Hypersensitive response (HR) is a form of programmed cell death (PCD) and the primary immune response that prevents pathogen invasion in plants. Here, we show that a microRNAmiR164 and its target gene NAC4 (At5g07680), encoding a NAC transcription factor, play essential roles in the regulation of HR PCD in Arabidopsis thaliana. Cell death symptoms were noticeably enhanced in NAC4-overexpressing (35S:NAC4) and mir164 mutant plants in response to avirulent bacterial pathogens. NAC4 expression was induced by pathogen infection and negatively regulated by miR164 expression. NAC4-binding DNA sequences were determined by in vitro binding site selection using random oligonucleotide sequences. Microarray, chromatin immunoprecipitation and quantitative real time polymerase chain reaction (qRT-PCR) analyses, followed by cell death assays in protoplasts, led to the identification of NAC4 target genes LURP1, WRKY40 and WRKY54, which act as negative regulators of cell death. Our results suggest that NAC4 promotes hypersensitive cell death by suppressing its target genes and this immune process is fine-tuned by the negative action of miR164.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/citología , Arabidopsis/metabolismo , MicroARNs/metabolismo , Factores de Transcripción/metabolismo , Arabidopsis/genética , Arabidopsis/inmunología , Proteínas de Arabidopsis/genética , Secuencia de Bases , Muerte Celular , Regulación de la Expresión Génica de las Plantas , Genes de Plantas , MicroARNs/genética , Inmunidad de la Planta/genética , Interferencia de ARNRESUMEN
Ethylene is a key signal in the regulation of plant defense responses. It is required for the expression and function of GDSL LIPASE1 (GLIP1) in Arabidopsis (Arabidopsis thaliana), which plays an important role in plant immunity. Here, we explore molecular mechanisms underlying the relationship between GLIP1 and ethylene signaling by an epistatic analysis of ethylene response mutants and GLIP1-overexpressing (35S:GLIP1) plants. We show that GLIP1 expression is regulated by ethylene signaling components and, further, that GLIP1 expression or application of petiole exudates from 35S:GLIP1 plants affects ethylene signaling both positively and negatively, leading to ETHYLENE RESPONSE FACTOR1 activation and ETHYLENE INSENSITIVE3 (EIN3) down-regulation, respectively. Additionally, 35S:GLIP1 plants or their exudates increase the expression of the salicylic acid biosynthesis gene SALICYLIC ACID INDUCTION-DEFICIENT2, known to be inhibited by EIN3 and EIN3-LIKE1. These results suggest that GLIP1 regulates plant immunity through positive and negative feedback regulation of ethylene signaling, and this is mediated by its activity to accumulate a systemic signal(s) in the phloem. We propose a model explaining how GLIP1 regulates the fine-tuning of ethylene signaling and ethylene-salicylic acid cross talk.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/enzimología , Arabidopsis/inmunología , Hidrolasas de Éster Carboxílico/metabolismo , Etilenos/metabolismo , Retroalimentación Fisiológica , Inmunidad de la Planta , Transducción de Señal/inmunología , Alternaria/fisiología , Arabidopsis/genética , Arabidopsis/microbiología , Proteínas de Arabidopsis/genética , Resistencia a la Enfermedad/genética , Resistencia a la Enfermedad/inmunología , Regulación hacia Abajo/genética , Epistasis Genética , Regulación de la Expresión Génica de las Plantas , Genes de Plantas/genética , Modelos Biológicos , Mutación/genética , Fenotipo , Enfermedades de las Plantas/genética , Enfermedades de las Plantas/inmunología , Enfermedades de las Plantas/microbiología , Exudados de Plantas/metabolismo , Inmunidad de la Planta/genética , Unión Proteica , Ácido Salicílico/metabolismo , Transducción de Señal/genética , Regulación hacia Arriba/genéticaRESUMEN
Annexins are Ca2+--and phospholipid-binding proteins that form an evolutionarily conserved multigene family throughout the animal and plant kingdoms. Two annexins, AnnAt1 and AnnAt4, have been identified as components in osmotic stress and abscisic acid signaling in Arabidopsis. Here, we report that AnnAt1 and AnnAt4 regulate plant stress responses in a light-dependent manner. The single-mutant annAt1 and annAt4 plants showed tolerance to drought and salt stress, which was greatly enhanced in double-mutant annAt1annAt4 plants, but AnnAt4-overexpressing transgenic plants (35S:AnnAt4) were more sensitive to stress treatments under long day conditions. Furthermore, expression of stress-related genes was altered in these mutant and transgenic plants. Upon dehydration and salt treatment, AtNCED3, encoding 9-cis-epoxycarotenoid dioxygenase, and P5CS1, encoding Δ-1-pyrroline-5-carboxylate synthase, which are key enzymes in ABA and proline synthesis, respectively, were highly induced in annAt1annAt4 plants and to a lesser extent in annAt1 and annAt4 plants, but not in 35S:AnnAt4 plants. While annAt1 plants were more drought sensitive, annAt4 plants were more tolerant in short days than in long days. In vitro and in vivo binding assays revealed that AnnAt1 and AnnAt4 bind to each other in a Ca2+-dependent manner. Our results suggest that AnnAt1 and AnnAt4 function cooperatively in response to drought and salt stress and their functions are affected by photoperiod.
Asunto(s)
Anexinas/metabolismo , Proteínas de Arabidopsis/metabolismo , Arabidopsis/genética , Sequías , Cloruro de Sodio/farmacología , Anexinas/genética , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Calcio/metabolismo , Regulación de la Expresión Génica de las Plantas , Germinación , Mutación , Fotoperiodo , Plantas Modificadas Genéticamente/genética , Plantas Modificadas Genéticamente/metabolismo , ARN de Planta/genética , Semillas/crecimiento & desarrollo , Estrés FisiológicoRESUMEN
Arabidopsis GDSL lipase 1 (GLIP1) has been shown to modulate systemic immunity through the regulation of ethylene signaling components. Here we demonstrate that the constitutive triple response mutant ctr1-1 requires GLIP1 for the ethylene response, gene expression, and pathogen resistance. The glip1-1 mutant was defective in induced resistance following primary inoculation of necrotrophic pathogens, whereas GLIP1-overexpressing plants showed resistance to multiple pathogens. Necrotrophic infection triggered the downregulation of EIN3 and the activation of ERF1 and SID2 in a GLIP1-dependent manner. These results suggest that GLIP1 positively and negatively regulates ethylene signaling, resulting in an ethylene-associated, necrotroph-induced immune response.