RESUMEN
Ubiquitins are small peptides that allow for posttranslational modification of proteins. Ubiquitin-related modifier (URM) proteins belong to the class of ubiquitin-like proteins. A primary function of URM proteins has been shown to be the sulfur transfer reaction leading to thiolation of tRNAs, a process that is important for accurate and effective protein translation. Recent analyses revealed that the Arabidopsis genome codes for two URM proteins, URM11 and URM12, which both are active in the tRNA thiolation process. Here, we show that URM11 and URM12 have overlapping expression patterns and are required for tRNA thiolation. The characterization of urm11 and urm12 mutants reveals that the lack of tRNA thiolation induces changes in general root architecture by influencing the rate of lateral root formation. In addition, they synergistically influence root hair cell growth. During the sulfur transfer reaction, URM proteins of different organisms interact with a thiouridylase, a protein-protein interaction that also takes place in Arabidopsis, since URM11 and URM12 interact with the Arabidopsis thiouridylase ROL5. Hence, the sulfur transfer reaction is conserved between distantly related species such as yeast, humans, and plants, and in Arabidopsis has an impact on root development.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/crecimiento & desarrollo , Raíces de Plantas/crecimiento & desarrollo , ARN de Transferencia/metabolismo , Proteínas Modificadoras Pequeñas Relacionadas con Ubiquitina/metabolismo , Compuestos de Azufre/metabolismo , Arabidopsis/metabolismo , ADN Complementario/genética , Perfilación de la Expresión Génica , Microscopía Fluorescente , Raíces de Plantas/metabolismo , ARN de Transferencia/genética , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Sulfurtransferasas/metabolismo , Técnicas del Sistema de Dos HíbridosRESUMEN
Plant cell growth is limited by the extension of cell walls, which requires both the synthesis and rearrangement of cell wall components in a controlled fashion. The target of rapamycin (TOR) pathway is a major regulator of cell growth in eukaryotes, and inhibition of this pathway by rapamycin reduces cell growth. Here, we show that in plants, the TOR pathway affects cell wall structures. LRR-extensin1 (LRX1) of Arabidopsis thaliana is an extracellular protein involved in cell wall formation in root hairs, and lrx1 mutants develop aberrant root hairs. rol5 (for repressor of lrx1) was identified as a suppressor of lrx1. The functionally similar ROL5 homolog in yeast, Ncs6p (needs Cla4 to survive 6), was previously found to affect TOR signaling. Inhibition of TOR signaling by rapamycin led to suppression of the lrx1 mutant phenotype and caused specific changes to galactan/rhamnogalacturonan-I and arabinogalactan protein components of cell walls that were similar to those observed in the rol5 mutant. The ROL5 protein accumulates in mitochondria, a target of the TOR pathway and major source of reactive oxygen species (ROS), and rol5 mutants show an altered response to ROS. This suggests that ROL5 might function as a mitochondrial component of the TOR pathway that influences the plant's response to ROS.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/citología , Pared Celular/metabolismo , Secuencia de Aminoácidos , Arabidopsis/genética , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Mapeo Cromosómico , Clonación Molecular , ADN de Plantas/genética , Regulación de la Expresión Génica de las Plantas , Genotipo , Mitocondrias/metabolismo , Datos de Secuencia Molecular , Mutagénesis , Fenotipo , Raíces de Plantas/citología , ARN de Transferencia/genética , Especies Reactivas de Oxígeno/metabolismo , Saccharomyces cerevisiae/metabolismo , Alineación de Secuencia , Transducción de Señal , Sirolimus/farmacologíaRESUMEN
Flavonoids are secondary metabolites known to modulate plant growth and development. A primary function of flavonols, a subgroup of flavonoids, is thought to be the modification of auxin fluxes in the plant. Flavonols in the cell are glycosylated, and the repressor of lrx1 (rol1) mutants of Arabidopsis thaliana, affected in rhamnose biosynthesis, have a modified flavonol glycosylation profile. A detailed analysis of the rol1-2 allele revealed hyponastic growth, aberrant pavement cell and stomatal morphology in cotyledons, and defective trichome formation. Blocking flavonoid biosynthesis suppresses the rol1-2 shoot phenotype, suggesting that it is induced by the modified flavonol profile. The hyponastic cotyledons of rol1-2 are likely to be the result of a flavonol-induced increase in auxin concentration. By contrast, the pavement cell, stomata, and trichome formation phenotypes appear not to be induced by the modified auxin distribution. Together, these results suggest that changes in the composition of flavonols can have a tremendous impact on plant development through both auxin-induced and auxin-independent processes.