RESUMEN
Purine nucleotides can be fully catabolized by plants to recycle nutrients. We have isolated a urate oxidase (uox) mutant of Arabidopsis thaliana that accumulates uric acid in all tissues, especially in the developing embryo. The mutant displays a reduced germination rate and is unable to establish autotrophic growth due to severe inhibition of cotyledon development and nutrient mobilization from the lipid reserves in the cotyledons. The uox mutant phenotype is suppressed in a xanthine dehydrogenase (xdh) uox double mutant, demonstrating that the underlying cause is not the defective purine base catabolism, or the lack of UOX per se, but the elevated uric acid concentration in the embryo. Remarkably, xanthine accumulates to similar levels in the xdh mutant without toxicity. This is paralleled in humans, where hyperuricemia is associated with many diseases whereas xanthinuria is asymptomatic. Searching for the molecular cause of uric acid toxicity, we discovered a local defect of peroxisomes (glyoxysomes) mostly confined to the cotyledons of the mature embryos, which resulted in the accumulation of free fatty acids in dry seeds. The peroxisomal defect explains the developmental phenotypes of the uox mutant, drawing a novel link between uric acid and peroxisome function, which may be relevant beyond plants.
Asunto(s)
Arabidopsis/enzimología , Peroxisomas/metabolismo , Urato Oxidasa/metabolismo , Ácido Úrico/metabolismo , Arabidopsis/embriología , Arabidopsis/genética , Arabidopsis/ultraestructura , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Cotiledón/embriología , Cotiledón/enzimología , Cotiledón/genética , Cotiledón/ultraestructura , Ácidos Grasos/metabolismo , Germinación , Mutación , Fenotipo , Componentes Aéreos de las Plantas/embriología , Componentes Aéreos de las Plantas/enzimología , Componentes Aéreos de las Plantas/genética , Componentes Aéreos de las Plantas/ultraestructura , Regiones Promotoras Genéticas/genética , Nucleótidos de Purina/metabolismo , Plantones/embriología , Plantones/enzimología , Plantones/genética , Plantones/ultraestructura , Semillas/embriología , Semillas/enzimología , Semillas/genética , Semillas/ultraestructura , Urato Oxidasa/genética , Ácido Úrico/química , Xantina/química , Xantina/metabolismo , Xantina Deshidrogenasa/genética , Xantina Deshidrogenasa/metabolismoRESUMEN
The transcription factor LEAFY COTYLEDON1 (LEC1) controls aspects of early embryogenesis and seed maturation in Arabidopsis thaliana. To identify components of the LEC1 regulon, transgenic plants were derived in which LEC1 expression was inducible by dexamethasone treatment. The cotyledon-like leaves and swollen root tips developed by these plants contained seed-storage compounds and resemble the phenotypes produced by increased auxin levels. In agreement with this, LEC1 was found to mediate up-regulation of the auxin synthesis gene YUCCA10. Auxin accumulated primarily in the elongation zone at the root-hypocotyl junction (collet). This accumulation correlates with hypocotyl growth, which is either inhibited in LEC1-induced embryonic seedlings or stimulated in the LEC1-induced long-hypocotyl phenotype, therefore resembling etiolated seedlings. Chromatin immunoprecipitation analysis revealed a number of phytohormone- and elongation-related genes among the putative LEC1 target genes. LEC1 appears to be an integrator of various regulatory events, involving the transcription factor itself as well as light and hormone signalling, especially during somatic and early zygotic embryogenesis. Furthermore, the data suggest non-embryonic functions for LEC1 during post-germinative etiolation.
Asunto(s)
Proteínas de Arabidopsis/genética , Arabidopsis/genética , Proteínas Potenciadoras de Unión a CCAAT/genética , Regulación de la Expresión Génica de las Plantas/genética , Reguladores del Crecimiento de las Plantas/metabolismo , Transducción de Señal/fisiología , Ácido Abscísico/metabolismo , Arabidopsis/embriología , Arabidopsis/crecimiento & desarrollo , Arabidopsis/ultraestructura , Proteínas de Arabidopsis/metabolismo , Brasinoesteroides/metabolismo , Proteínas Potenciadoras de Unión a CCAAT/metabolismo , Perfilación de la Expresión Génica , Hipocótilo/embriología , Hipocótilo/genética , Hipocótilo/crecimiento & desarrollo , Hipocótilo/ultraestructura , Ácidos Indolacéticos/metabolismo , Luz , Mutación , Motivos de Nucleótidos , Análisis de Secuencia por Matrices de Oligonucleótidos , Componentes Aéreos de las Plantas/embriología , Componentes Aéreos de las Plantas/genética , Componentes Aéreos de las Plantas/crecimiento & desarrollo , Componentes Aéreos de las Plantas/ultraestructura , Técnicas de Embriogénesis Somática de Plantas , Plantas Modificadas Genéticamente , Plantones/embriología , Plantones/genética , Plantones/crecimiento & desarrollo , Plantones/ultraestructura , Semillas/embriología , Semillas/genética , Semillas/crecimiento & desarrollo , Semillas/ultraestructura , Regulación hacia Arriba/genéticaRESUMEN
The functions of the plant body rely on interactions among distinct and nonequivalent cell types. The comparison of transcriptomes from different cell types should expose the transcriptional networks that underlie cellular attributes and contributions. Using laser microdissection and microarray profiling, we have produced a cell type transcriptome atlas that includes 40 cell types from rice (Oryza sativa) shoot, root and germinating seed at several developmental stages, providing patterns of cell specificity for individual genes and gene classes. Cell type comparisons uncovered previously unrecognized properties, including cell-specific promoter motifs and coexpressed cognate binding factor candidates, interaction partner candidates and hormone response centers. We inferred developmental regulatory hierarchies of gene expression in specific cell types by comparison of several stages within root, shoot and embryo.