RESUMEN
MAIN CONCLUSION: An exonuclease V homologue from apomictic Brachiaria brizantha is expressed and localized in nucellar cells at key moments when these cells differentiate to give rise to unreduced gametophytes. Brachiaria is a genus of forage grasses with economical and agricultural importance to Brazil. Brachiaria reproduces by aposporic apomixis, in which unreduced embryo sacs, derived from nucellar cells, other than the megaspore mother cell (MMC), are formed. The unreduced embryo sacs produce an embryo without fertilization resulting in clones of the mother plant. Comparative gene expression analysis in ovaries of sexual and apomictic Brachiaria spp. revealed a sequence from B. brizantha that showed a distinct pattern of expression in ovaries of sexual and apomictic plants. In this work, we describe a gene named BbrizExoV with strong identity to exonuclease V (Exo V) genes from other grasses. Sequence analysis in signal prediction tools showed that BbrizExoV might have dual localization, depending on the translation point. A longer form to the nucleus and a shorter form which would be directed to the chloroplast. This is also the case for monocot sequences analyzed from other species. The long form of BbrizExoV protein localizes to the nucleus of onion epidermal cells. Analysis of ExoV proteins from dicot species, with exception of Arabidopsis thaliana ExoVL protein, showed only one localization. Using a template-based AlphaFold 2 modelling approach the structure of BbrizExoV in complex with metal and ssDNA was predicted based on the holo structure of the human counterpart. Features predicted to define ssDNA binding but a lack of sequence specificity are shared between the human enzyme and BbrizExoV. Expression analyses indicated the precise site and timing of transcript accumulation during ovule development, which coincides with the differentiation of nucelar cells to form the typical aposporic four-celled unreduced gametophyte. A putative function for this protein is proposed based on its homology and expression pattern.
Asunto(s)
Apomixis , Arabidopsis , Brachiaria , Humanos , Exodesoxirribonucleasa V , Gametogénesis en la Planta , Células Germinativas de las Plantas , PoaceaeRESUMEN
RecBCD and RecFOR homologous recombination pathways induced bacterial chromosomal duplication-segregation by sodium selenite (SSe) at sub-inhibitory concentrations. This evidence suggests that SSe induces both, double and single DNA strand damage with a concomitant DNA repair response, however the strong dependence for recombinogenic activity of RecB product suggests that the main DNA repair pathway copes with dsDNA breaks. A role for SSe recombinogenic induction is proposed to explain its effect on DNA instability.
Asunto(s)
Deleción Cromosómica , Cromosomas Bacterianos/efectos de los fármacos , Cromosomas Bacterianos/genética , Exodesoxirribonucleasa V/metabolismo , Salmonella typhimurium/efectos de los fármacos , Salmonella typhimurium/genética , Selenito de Sodio/toxicidad , Proteínas Bacterianas/metabolismo , Daño del ADN , Reparación del ADN , Proteínas de Unión al ADN/metabolismo , Genes Bacterianos , Recombinación Genética , Salmonella typhimurium/metabolismoRESUMEN
Precise excision of transposons Tn10 and mini-Tn10 is increased in the dnaB252 thermosensitive mutant of Escherichia coli K12, at the permissive temperature. DNA repair proteins like Pol II, RecF, Ruv and RecA were found to participate, to different extents, in this induced excision event. In this work we report that DNA repair-recombination protein RecBCD has a predominant role in this deletion process. The role of this and other repair proteins in DNA replication of the dnaB mutant in relation to the excision of the transposon is analyzed.
Asunto(s)
ADN Helicasas/genética , Reparación del ADN/fisiología , Elementos Transponibles de ADN , ADN Bacteriano/metabolismo , Proteínas de Escherichia coli/metabolismo , Exodesoxirribonucleasa V/metabolismo , Mutación , Proteínas Bacterianas/genética , Proteínas Bacterianas/metabolismo , ADN Helicasas/metabolismo , ADN Bacteriano/genética , AdnB Helicasas , Escherichia coli/enzimología , Escherichia coli/genética , Proteínas de Escherichia coli/genética , Exodesoxirribonucleasa V/genéticaRESUMEN
Mitomycin C (MMC) treatment or mutations in uvrD enhance the frequency of Tn10 precise excision. We have shown previously that several repair-recombination genes, such as recA, ruv and recF are involved in the induced excision process. In this study, we find that other genes belonging to the RecBC and RecF sexual recombination pathways also participate in this process since mutations in recB, sbcB or recO diminish, though to different degrees, the frequency of Tn10 precise excision induced by MMC treatment or by uvrD mutants. Pairwise combinations of some of these mutations were also tested for Tn10 induced precise excision; most of these double mutants showed additive effects in reducing the frequency of the excision process. The results of these studies suggest that recombinational-repair genes, particularly recF, sbcB and recO have different roles in the induced excision of Tn10 than in recombinational mating.