RESUMO
Nitrate can act as a potent signal to control growth and development in plants. In this study, we show that nitrate is able to stimulate primary root growth via increased meristem activity and cytokinin signaling. Cytokinin perception and biosynthesis mutants displayed shorter roots as compared with wild-type plants when grown with nitrate as the only nitrogen source. Histological analysis of the root tip revealed decreased cell division and elongation in the cytokinin receptor double mutant ahk2/ahk4 as compared with wild-type plants under a sufficient nitrate regime. Interestingly, a nitrate-dependent root growth arrest was observed between days 5 and 6 after sowing. Wild-type plants were able to recover from this growth arrest, while cytokinin signaling or biosynthesis mutants were not. Transcriptome analysis revealed significant changes in gene expression after, but not before, this transition in contrasting genotypes and nitrate regimes. We identified genes involved in both cell division and elongation as potentially important for primary root growth in response to nitrate. Our results provide evidence linking nitrate and cytokinin signaling for the control of primary root growth in Arabidopsis thaliana.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Citocininas/biossíntese , Nitratos/metabolismo , Raízes de Plantas/crescimento & desenvolvimento , Raízes de Plantas/metabolismo , Transdução de Sinais/fisiologia , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Divisão Celular , Regulação da Expressão Gênica de Plantas , Genes de Plantas , Histidina Quinase/metabolismo , Meristema/metabolismo , Mutação , Raízes de Plantas/citologia , Proteínas Quinases/metabolismo , Receptores de Superfície Celular/metabolismoRESUMO
Nitrate acts as a potent signal to control global gene expression in Arabidopsis. Using an integrative bioinformatics approach we identified TGA1 and TGA4 as putative regulatory factors that mediate nitrate responses in Arabidopsis roots. We showed that both TGA1 and TGA4 mRNAs accumulate strongly after nitrate treatments in roots. Global gene expression analysis revealed 97% of the genes with altered expression in tga1 tga4 double mutant plants respond to nitrate treatments, indicating that these transcription factors have a specific role in nitrate responses in Arabidopsis root organs. We found TGA1 and TGA4 regulate the expression of nitrate transporter genes NRT2.1 and NRT2.2. Specific binding of TGA1 to its cognate DNA sequence on NRT2.1 and NRT2.2 promoters was confirmed by chromatin immunoprecipitation assays. The tga1 tga4 double mutant plants exhibit nitrate-dependent lateral and primary root phenotypes. Lateral root initiation is affected in both tga1 tga4 and nrt1.2 nrt2.2 double mutants, suggesting TGA1 and TGA4 regulate lateral root development at least partly via NRT2.1 and NRT2.2. Additional root phenotypes of tga1 tga4 double mutants indicate that these transcription factors play an important role in root developmental responses to nitrate. These results identify TGA1 and TGA4 as important regulatory factors of the nitrate response in Arabidopsis roots.
Assuntos
Arabidopsis/genética , Fatores de Transcrição de Zíper de Leucina Básica/genética , Regulação da Expressão Gênica de Plantas , Nitratos/metabolismo , Arabidopsis/crescimento & desenvolvimento , Arabidopsis/metabolismo , Fatores de Transcrição de Zíper de Leucina Básica/metabolismo , Biologia Computacional , Redes Reguladoras de Genes , Mutação , Fenótipo , Raízes de Plantas/genética , Raízes de Plantas/crescimento & desenvolvimento , Raízes de Plantas/metabolismo , Regiões Promotoras Genéticas/genética , Transdução de Sinais , Transcriptoma , Regulação para CimaRESUMO
Nitrogen (N) is an essential macronutrient for plants. In nature, N cycles between different inorganic and organic forms some of which can serve as nutrients for plants. The inorganic N forms nitrate and ammonium are the most important sources of N for plants. However, plants can also uptake and use organic N forms such as amino acids and urea. Besides their nutritional role, nitrate and other forms of N can also act as signals that regulate the expression of hundreds of genes causing modulation of plant metabolism, physiology, growth, and development. Although many genes and processes affected by changes in external or internal N have been identified, the molecular mechanisms involved in N sensing and signaling are still poorly understood. Classic reverse and forward genetics and more recently the advent of genomic and systems approaches have helped to characterize some of the components of the signaling pathways directing Arabidopsis responses to N. Here, we provide an update on recent advances to identify the components involved in N sensing and signaling in Arabidopsis and their importance for the plant response to N.