RESUMO
Cyclic adenosine diphosphate (ADP)-ribose (cADPR) isomers are signaling molecules produced by bacterial and plant Toll/interleukin-1 receptor (TIR) domains via nicotinamide adenine dinucleotide (oxidized form) (NAD+) hydrolysis. We show that v-cADPR (2'cADPR) and v2-cADPR (3'cADPR) isomers are cyclized by O-glycosidic bond formation between the ribose moieties in ADPR. Structures of 2'cADPR-producing TIR domains reveal conformational changes that lead to an active assembly that resembles those of Toll-like receptor adaptor TIR domains. Mutagenesis reveals a conserved tryptophan that is essential for cyclization. We show that 3'cADPR is an activator of ThsA effector proteins from the bacterial antiphage defense system termed Thoeris and a suppressor of plant immunity when produced by the effector HopAM1. Collectively, our results reveal the molecular basis of cADPR isomer production and establish 3'cADPR in bacteria as an antiviral and plant immunity-suppressing signaling molecule.
Assuntos
ADP-Ribosil Ciclase , Proteínas Adaptadoras de Transporte Vesicular , Bactérias , Proteínas de Bactérias , ADP-Ribose Cíclica , Imunidade Vegetal , Receptores Toll-Like , ADP-Ribosil Ciclase/química , ADP-Ribosil Ciclase/genética , ADP-Ribosil Ciclase/metabolismo , Proteínas Adaptadoras de Transporte Vesicular/química , Proteínas Adaptadoras de Transporte Vesicular/genética , Proteínas Adaptadoras de Transporte Vesicular/metabolismo , Bactérias/imunologia , Bactérias/virologia , Proteínas de Bactérias/química , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , ADP-Ribose Cíclica/biossíntese , ADP-Ribose Cíclica/química , Isomerismo , NAD/metabolismo , Domínios Proteicos , Receptores de Interleucina-1/química , Transdução de Sinais , Receptores Toll-Like/química , Receptores Toll-Like/genética , Receptores Toll-Like/metabolismo , Triptofano/química , Triptofano/genéticaRESUMO
Histone acetylation is directly related to gene expression. In yeast, the acetyltransferase general control nonderepressible-5 (GCN5) targets histone H3 and associates with transcriptional co-activators alteration/deficiency in activation-2 (ADA2) and alteration/deficiency in activation-3 (ADA3) in complexes like SAGA. Arabidopsis thaliana has two genes encoding proteins, designated ADA3a and ADA3b, that correspond to yeast ADA3. We investigated the role of ADA3a and ADA3b in regulating gene expression during flowering time. Specifically, we found that knock out mutants ada3a-2 and the double mutant ada3a-2 ada3b-2 lead to early flowering compared to the wild type plants under long day (LD) conditions and after moving plants from short days to LD. Consistent with ADA3a being a repressor of floral initiation, FLOWERING LOCUS T (FT) expression was increased in ada3a mutants. In contrast, other genes involved in multiple pathways leading to floral transition, including FT repressors, players in GA signaling, and members of the SPL transcriptional factors, displayed reduced expression. Chromatin immunoprecipitation analysis revealed that ADA3a affects the histone H3K14 acetylation levels in SPL3, SPL5, RGA, GAI, and SMZ loci. In conclusion, ADA3a is involved in floral induction through a GCN5-containing complex that acetylates histone H3 in the chromatin of flowering related genes.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Flores/fisiologia , Proteínas Nucleares/metabolismo , Transcrição Gênica , Acetilação , Arabidopsis/genética , Proteínas de Arabidopsis/química , Proteínas de Arabidopsis/genética , DNA Bacteriano/genética , Epistasia Genética , Flores/genética , Regulação da Expressão Gênica de Plantas , Genoma de Planta , Histonas/metabolismo , Mutação/genética , Proteínas Nucleares/química , Proteínas Nucleares/genética , Fenótipo , Filogenia , Ligação Proteica , Domínios Proteicos , Homologia de Sequência de Aminoácidos , Fatores de TempoRESUMO
Maintaining fertility in a fluctuating environment is key to the reproductive success of flowering plants. Meiosis and pollen formation are particularly sensitive to changes in growing conditions, especially temperature. We have previously identified cyclin-dependent kinase G1 (CDKG1) as a master regulator of temperature-dependent meiosis and this may involve the regulation of alternative splicing (AS), including of its own transcript. CDKG1 mRNA can undergo several AS events, potentially producing two protein variants: CDKG1L and CDKG1S, differing in their N-terminal domain which may be involved in co-factor interaction. In leaves, both isoforms have distinct temperature-dependent functions on target mRNA processing, but their role in pollen development is unknown. In the present study, we characterize the role of CDKG1L and CDKG1S in maintaining Arabidopsis fertility. We show that the long (L) form is necessary and sufficient to rescue the fertility defects of the cdkg1-1 mutant, while the short (S) form is unable to rescue fertility. On the other hand, an extra copy of CDKG1L reduces fertility. In addition, mutation of the ATP binding pocket of the kinase indicates that kinase activity is necessary for the function of CDKG1. Kinase mutants of CDKG1L and CDKG1S correctly localize to the cell nucleus and nucleus and cytoplasm, respectively, but are unable to rescue either the fertility or the splicing defects of the cdkg1-1 mutant. Furthermore, we show that there is partial functional overlap between CDKG1 and its paralog CDKG2 that could in part be explained by overlapping gene expression.