RESUMO
Arabidopsis dnd1 and dnd2 mutants lack cyclic nucleotide-gated ion channel proteins and carry out avirulence or resistance gene-mediated defense with a greatly reduced hypersensitive response (HR). They also exhibit elevated broad-spectrum disease resistance and constitutively elevated salicylic acid (SA) levels. We examined the contributions of NPR1, SID2 (EDS16), NDR1, and EIN2 to dnd phenotypes. Mutations that affect SA accumulation or signaling (sid2, npr1, and ndr1) abolished the enhanced resistance of dnd mutants against Pseudomonas syringae pv. tomato and Hyaloperonospora parasitica but not Botrytis cinerea. When SA-associated pathways were disrupted, the constitutive activation of NPR1-dependent and NPR1-independent and SA-dependent pathways was redirected toward PDF1.2-associated pathways. This PDF1.2 overexpression was downregulated after infection by P. syringae. Disruption of ethylene signaling abolished the enhanced resistance to B. cinerea but not P. syringae or H. parasitica. However, loss of NPR1, SID2, NDR1, or EIN2 did not detectably alter the reduced HR in dnd mutants. The susceptibility of dnd ein2 plants to B. cinerea despite their reduced-HR phenotype suggests that cell death repression is not the primary cause of dnd resistance to necrotrophic pathogens. The partial restoration of resistance to B. cinerea in dnd1 npr1 ein2 triple mutants indicated that this resistance is not entirely EIN2 dependent. The above findings indicate that the broad-spectrum resistance of dnd mutants occurs due to activation or sensitization of multiple defense pathways, yet none of the investigated pathways are required for the reduced-HR phenotype.
Assuntos
Proteínas de Arabidopsis/fisiologia , Arabidopsis/crescimento & desenvolvimento , Transdução de Sinais/fisiologia , Arabidopsis/genética , Arabidopsis/microbiologia , Proteínas de Arabidopsis/genética , Northern Blotting , Botrytis/fisiologia , Regulação da Expressão Gênica de Plantas , Interações Hospedeiro-Patógeno , Imunidade Inata/genética , Transferases Intramoleculares/genética , Transferases Intramoleculares/fisiologia , Doenças das Plantas/genética , Doenças das Plantas/microbiologia , Plantas Geneticamente Modificadas/genética , Plantas Geneticamente Modificadas/crescimento & desenvolvimento , Plantas Geneticamente Modificadas/microbiologia , Pseudomonas syringae/fisiologia , Receptores de Superfície Celular/genética , Receptores de Superfície Celular/fisiologia , Ácido Salicílico/metabolismo , Transdução de Sinais/genética , Fatores de Transcrição/genética , Fatores de Transcrição/fisiologiaRESUMO
O-GlcNAc transferase (OGT) catalyses transfer of GlcNAc (N-acetylglucosamine) to serine or threonine of proteins. The Arabidopsis OGTs, SECRET AGENT (SEC) and SPINDLY (SPY) have overlapping functions during gametogenesis and embryogenesis. SPY functions in a number of processes including circadian, light, and gibberellin (GA) responses. The role of SEC in plant development and GA signalling was investigated by determining the phenotypes of sec-1 and sec-2 plants and the expression pattern of SEC. Similar to SPY, SEC transcripts were ubiquitous. Although there is no evidence of transcript-level regulation by other factors, SEC mRNA levels are elevated in spy plants and SPY mRNA levels are elevated in sec plants. sec-1 and sec-2 plants exhibited few of the defects observed in spy plants and had wild-type GA responses. Compared with wild type, sec plants produced leaves at a reduced rate. Haplo-insufficiency at SEC in a spy ga1 double mutant background suppressed spy during germination and enhanced the production of ovaries with four carpels by spy. By contrast, SPY haplo-insufficiency in a sec ga1 double mutant background caused a novel phenotype, production of a proliferation of pin-like structures instead of a floral shoot. These results are consistent with SEC function overlapping with SPY for leaf production and reproductive development.
Assuntos
Proteínas de Arabidopsis/fisiologia , Arabidopsis/crescimento & desenvolvimento , N-Acetilglucosaminiltransferases/fisiologia , Proteínas Repressoras/fisiologia , Arabidopsis/anatomia & histologia , Arabidopsis/fisiologia , Proteínas de Arabidopsis/genética , Giberelinas/metabolismo , Imunidade Inata/fisiologia , Meristema/crescimento & desenvolvimento , Meristema/metabolismo , Meristema/fisiologia , Mutação , N-Acetilglucosaminiltransferases/genética , Fenótipo , Folhas de Planta/crescimento & desenvolvimento , Proteínas Repressoras/genéticaRESUMO
Demethylation of DNA promotes flowering in plants from the vernalization-responsive ecotype C24 of Arabidopsis thaliana (L.) Heynh., but delays flowering in the ecotype Landsberg erecta which is not responsive to vernalization. To investigate these contrasting effects of low methylation we have monitored flowering times and expression of two repressors of flowering, FLC and FWA, in low-methylation plants from three late-flowering mutants in the ecotype Landsberg erecta. Demethylation of DNA decreased FLC expression in the vernalization-responsive mutants, but was not associated with a promotion of flowering; rather, in some lines, demethylation delayed flowering. The opposing effects of demethylation could be explained by its differential effect on the expression of two repressors of flowering. FLC was down-regulated in plants with low methylation, promoting flowering, while FWA was activated in response to demethylation, which probably delays the transition to flowering. Expression of the FWA gene did not delay flowering in plants of ecotype C24; our data suggest that the FWA protein of C24 may be non-functional.