RESUMEN
The aminoglycoside antibiotic hygromycin B (Hyg) inhibits prokaryotic, chloroplast and mitochondrial protein synthesis. Because of the toxic effect of Hyg on plant cells, the HPT gene, encoding hygromycin phosphotransferase, has become one of the most widely used selectable markers in plant transformation. Yet the mechanism behind Hyg-induced cell lethality in plants is not clearly understood. In this study, we aimed to decipher this mechanism. With Hyg treatment, rice calli exhibited cell death, and rice seedlings showed severe growth defects, leaf chlorosis and leaf shrinkage. Rice seedlings also exhibited severe lipid peroxidation and protein carbonylation, for oxidative stress damage at the cellular level. The production of reactive oxygen species such as O2(·-), H2O2 and OH(·) was greatly induced in rice seedlings under Hyg stress, and pre-treatment with ascorbate increased resistance to Hyg-induced toxicity indicating the existence of oxidative stress. Overexpression of mitochondrial Alternative oxidase1a gene without HPT selection marker in rice enhanced tolerance to Hyg and attenuated the degradation of protein content, whereas the rice plastidial glutathione reductase 3 mutant showed increased sensitivity to Hyg. These results demonstrate that Hyg-induced cell lethality in rice is not only due to the inhibition of protein synthesis but also mediated by oxidative stress.
Asunto(s)
Higromicina B/toxicidad , Oryza/efectos de los fármacos , Antibacterianos/toxicidad , Muerte Celular/efectos de los fármacos , Genes de Plantas , Glutatión Reductasa/genética , Proteínas Mitocondriales/genética , Mutación , Oryza/citología , Oryza/metabolismo , Estrés Oxidativo/efectos de los fármacos , Oxidorreductasas/genética , Fosfotransferasas (Aceptor de Grupo Alcohol)/genética , Proteínas de Plantas/genética , Plantas Modificadas Genéticamente , Especies Reactivas de Oxígeno/metabolismo , Plantones/citología , Plantones/efectos de los fármacos , Plantones/metabolismoRESUMEN
Post-translational modifications of core histones are important for various DNA-templated processes such as transcription and repair. We recently reported that the ALFIN LIKE 6 (AL6) gene, identified in a forward genetic screen, is critical for phosphate deficiency-induced root hair formation and several other processes associated with the regulation of cellular phosphate homeostasis. AL6 contains a Plant Homeo Domain (PHD) finger that can bind to trimethylated lysine 4 of histone H3 (H3K4me3). Homozygous mutants defective in AL6 expression form very short root hairs under phosphate-deficient conditions, presumably caused by altered expression of putative primary and secondary down-stream targets of AL6. In this Addendum, we speculate about possible roles of AL6, H3K4 trimethylation and other chromatin modifications in the adaptation of plants to low phosphate availability.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Histonas/metabolismo , Proteínas de Homeodominio/metabolismo , Fosfatos/metabolismo , Factores de Transcripción/metabolismo , MetilaciónRESUMEN
Phosphate (Pi) starvation in plants induces dense and elongated root hairs, which increase the absorptive surface area of the roots and play a critical role in Pi uptake. The molecular mechanism underlying these changes remains unclear. Forward and reverse genetic approaches were employed to identify novel genes involved in root hair formation on Pi starvation. The mutant per2, with defects in root hair elongation specifically under low Pi conditions, was identified in a large-scale genetic screen of T-DNA insertion lines. The phenotype was caused by a mutation in the homeodomain protein ALFIN-LIKE 6 (AL6). From a screen of mutants defective in genes that showed lower transcript abundance in per2 relative to wild-type roots on low Pi medium, we identified four putative downstream targets of AL6, namely ETC1, NPC4, SQD2 and PS2, all of which were critical in root hair elongation of Pi-deficient plants. The results further indicate that AL6 is involved in the control of growth and several key responses to Pi starvation. Our findings demonstrate that AL6 controls the transcription of a suite of genes critical for root hair elongation under low Pi conditions, suggesting a novel physiological function for an Alfin gene in Arabidopsis.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/crecimiento & desarrollo , Proteínas de Homeodominio/metabolismo , Fosfatos/metabolismo , Raíces de Plantas/crecimiento & desarrollo , Factores de Transcripción/metabolismo , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Unión al ADN/genética , Regulación de la Expresión Génica de las Plantas , Hexosiltransferasas/genética , Proteínas de Homeodominio/genética , Homeostasis , Metales/metabolismo , Mutación , Fosfatos/deficiencia , Raíces de Plantas/genética , Plantas Modificadas Genéticamente , Factores de Transcripción/genética , Fosfolipasas de Tipo C/genéticaRESUMEN
Root hair morphogenesis is driven by an amalgam of interacting processes controlled by complex signaling events. Redox processes and transcriptional control are critical for root hair development. However, the molecular mechanisms that integrate redox state and transcription are largely unknown. To elucidate a possible role of transcriptional Mediators in root hair formation, we analyzed the Arabidopsis root hair phenotype of T-DNA insertion lines that harbor homozygous mutations in genes encoding Mediator subunits. Genetic evidence indicates that the Mediator subunits PFT1/MED25 and MED8 are critical for root hair differentiation, but act via separate mechanisms. Transcriptional profiling of pft1 roots revealed that PFT1 activates a subset of hydrogen peroxide (H(2)O(2))-producing class III peroxidases. pft1 mutants showed perturbed H(2)O(2) and superoxide (O(2)(·-)) distribution, suggesting that PFT1 is essential to maintain redox homeostasis in the root. Chemical treatments rescued the pft1 mutant phenotype, indicating that correct reactive oxygen species (ROS) distribution is an essential prerequisite for root hair differentiation. In addition, PFT1 positively regulates cell wall remodeling genes that are essential for root hair formation. Our results demonstrate that PFT1 maintains ROS distribution which, in turn, controls root hair differentiation. Thus, our findings reveal a novel mechanism in which the Mediator controls ROS homeostasis by regulating the transcriptional machinery.