RESUMEN
Under environmental stress, plants are believed to actively repress their growth to save resource and alter its allocation to acquire tolerance against the stress. Although a lot of studies have uncovered precise mechanisms for responding to stress and acquiring tolerance, the mechanisms for regulating growth repression under stress are not as well understood. It is especially unclear which particular genes related to cell cycle control are involved in active growth repression. Here, we showed that decreased growth in plants exposed to moderate salt stress is mediated by MYB3R transcription factors that have been known to positively and negatively regulate the transcription of G2/M-specific genes. Our genome-wide gene expression analysis revealed occurrences of general downregulation of G2/M-specific genes in Arabidopsis under salt stress. Importantly, this downregulation is significantly and universally mitigated by the loss of MYB3R repressors by mutations. Accordingly, the growth performance of Arabidopsis plants under salt stress is significantly recovered in mutants lacking MYB3R repressors. This growth recovery involves improved cell proliferation that is possibly due to prolonging and accelerating cell proliferation, which were partly suggested by enlarged root meristem and increased number of cells positive for CYCB1;1-GUS. Our ploidy analysis further suggested that cell cycle progression at the G2 phase was delayed under salt stress, and this delay was recovered by loss of MYB3R repressors. Under salt stress, the changes in expression of MYB3R activators and repressors at both the mRNA and protein levels were not significant. This observation suggests novel mechanisms underlying MYB3R-mediated growth repression under salt stress that are different from the mechanisms operating under other stress conditions such as DNA damage and high temperature.
Asunto(s)
Proteínas de Arabidopsis , Arabidopsis , Arabidopsis/genética , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Ciclo Celular , Regulación de la Expresión Génica de las Plantas , Plantas Modificadas Genéticamente/metabolismo , Estrés Salino , Estrés FisiológicoRESUMEN
For anti-bioterrorism measures against the use of Bacillus anthracis, a double-color fluorescence in situ hybridization (FISH) is proposed, for the rapid and specific detection of B. anthracis. The probes were designed based on the differences in 16S and 23S rRNA genes of B. cereus group. A new permeabilization protocol was developed to enhance the permeability of FISH probes into B. anthracis spores. The highest detection rate (90.8 ± 0.69) of B. anthracis spores by FISH was obtained with successive incubation steps with 50% ethanol at 80 °C, a mixture of SDS/DTT solution (10mg/ml SDS, 50mM DTT) at 65 °C and finally in a lysozyme solution (20mg/ml) at 37 °C for 30 min each. This protocol was evaluated for the detection of B. anthracis spores in soil and air samples after adding formalin-fixed spores at different densities. The results have proven the success of double-color FISH in detecting B. anthracis spores in air samples in the range of 10(3) spores/m(3) and above. Conversely, for detecting B. anthracis spores in a soil sample, the lowest detection limit was found to be 10(7) spores/g dry soils. These results confirm the applicability of the developed permeabilization protocol, combined with the double-color FISH technique in specific detection of B. anthracis in soil and air samples.
Asunto(s)
Bacillus anthracis/aislamiento & purificación , Técnicas Bacteriológicas/métodos , Microbiología Ambiental , Hibridación Fluorescente in Situ/métodos , Microscopía Fluorescente/métodos , Esporas Bacterianas/aislamiento & purificación , Coloración y Etiquetado/métodos , Bacillus anthracis/genética , Permeabilidad de la Membrana Celular/efectos de los fármacos , Humanos , Sondas de Oligonucleótidos/genética , Sondas de Oligonucleótidos/metabolismo , ARN Ribosómico 16S/genética , ARN Ribosómico 23S/genética , Manejo de Especímenes/métodos , Esporas Bacterianas/genéticaRESUMEN
During the plant cell cycle, genes preferentially expressed at the G2/M phase are regulated by R1R2R3-type Myb transcription factors. To address the function of 2 tobacco R1R2R3-Myb proteins, NtmybA1 and NtmybA2, we generated transgenic tobacco plants in which endogenous NtmybA2 transcripts were significantly decreased, presumably due to cosuppression triggered by the presence of the NtmybA2 transgene. These lines showed a concomitant downregulation of structurally related NtmybA1 and many G2/M-expressed genes. In the cosuppression plants, we found a dwarf phenotype due to both reduced cell size and decreased cell number. Our results provide evidence confirming our previous view that NtmybA1 and NtmybA2 may regulate cell expansion as well as cell division by transcriptionally activating many G2/M-expressed genes in tobacco.