RESUMO
⢠Legume roots develop two types of lateral organs, lateral roots and nodules. Nodules develop as a result of a symbiotic interaction with rhizobia and provide a niche for the bacteria to fix atmospheric nitrogen for the plant. ⢠The Arabidopsis NAC1 transcription factor is involved in lateral root formation, and is regulated post-transcriptionally by miRNA164 and by SINAT5-dependent ubiquitination. We analyzed in Medicago truncatula the role of the closest NAC1 homolog in lateral root formation and in nodulation. ⢠MtNAC1 shows a different expression pattern in response to auxin than its Arabidopsis homolog and no changes in lateral root number or nodulation were observed in plants affected in MtNAC1 expression. In addition, no interaction was found with SINA E3 ligases, suggesting that post-translational regulation of MtNAC1 does not occur in M. truncatula. Similar to what was found in Arabidopsis, a conserved miR164 target site was retrieved in MtNAC1, which reduced protein accumulation of a GFP-miR164 sensor. Furthermore, miR164 and MtNAC1 show an overlapping expression pattern in symbiotic nodules, and overexpression of this miRNA led to a reduction in nodule number. ⢠This work suggests that regulatory pathways controlling a conserved transcription factor are complex and divergent between M. truncatula and Arabidopsis.
Assuntos
Medicago truncatula/fisiologia , Proteínas de Plantas/metabolismo , Sinorhizobium meliloti/fisiologia , Fatores de Transcrição/metabolismo , Sequência de Aminoácidos , Arabidopsis/genética , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Sequência de Bases , Flores/efeitos dos fármacos , Flores/genética , Flores/fisiologia , Regulação da Expressão Gênica de Plantas , Ácidos Indolacéticos/farmacologia , Medicago truncatula/efeitos dos fármacos , Medicago truncatula/genética , MicroRNAs/genética , Dados de Sequência Molecular , Mutação , Filogenia , Folhas de Planta/efeitos dos fármacos , Folhas de Planta/genética , Folhas de Planta/fisiologia , Proteínas de Plantas/química , Proteínas de Plantas/genética , Nodulação/genética , Raízes de Plantas/efeitos dos fármacos , Raízes de Plantas/genética , Raízes de Plantas/fisiologia , Brotos de Planta/efeitos dos fármacos , Brotos de Planta/genética , Brotos de Planta/fisiologia , Plantas Geneticamente Modificadas/efeitos dos fármacos , Plantas Geneticamente Modificadas/genética , Plantas Geneticamente Modificadas/fisiologia , Estrutura Terciária de Proteína , RNA de Plantas/genética , Proteínas Recombinantes de Fusão , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , Nicotiana/genética , Nicotiana/metabolismo , Transativadores/genética , Transativadores/metabolismo , Fatores de Transcrição/química , Fatores de Transcrição/genéticaRESUMO
The symbiotic interaction between legumes and rhizobia results in root nodules with nitrogen-fixing bacteroids. Throughout the lifespan of the nodules, the exchange of C sources and N compounds between the host plant and the bacteria is tightly balanced. Sucrose plays a major role in the provision of C skeletons and energy to the bacteroids. Transcription of MtATB2, encoding a bZIP transcription factor, is shown to be regulated by sucrose and is enhanced during nodule senescence. Transcripts occur in the nodule apex and in the vascular tissue of nodules and roots. Ectopic expression of the gene diminished nodule formation and affected root growth. Presumably, MtATB2 controls processes that are under sucrose homeostasis and are important for nodule and root growth.
Assuntos
Fatores de Transcrição de Zíper de Leucina Básica/metabolismo , Medicago truncatula/genética , Proteínas de Plantas/metabolismo , Nodulação/genética , Sacarose/metabolismo , Sequência de Aminoácidos , Sequência de Bases , Fatores de Transcrição de Zíper de Leucina Básica/genética , Clonagem Molecular , Regulação da Expressão Gênica de Plantas , Medicago truncatula/metabolismo , Medicago truncatula/microbiologia , Dados de Sequência Molecular , Proteínas de Plantas/genética , Plantas Geneticamente Modificadas/genética , Plantas Geneticamente Modificadas/metabolismo , Plantas Geneticamente Modificadas/microbiologia , RNA de Plantas/genética , Análise de Sequência de DNA , Simbiose , Nicotiana/genética , Nicotiana/metabolismoRESUMO
The CLAVATA3/embryo-surrounding region (CLE) peptides control the fine balance between proliferation and differentiation in plant development. We studied the role of CLE peptides during indeterminate nodule development and identified 25 MtCLE peptide genes in the Medicago truncatula genome, of which two genes, MtCLE12 and MtCLE13, had nodulation-related expression patterns that were linked to proliferation and differentiation. MtCLE13 expression was up-regulated early in nodule development. A high-to-low expression gradient radiated from the inner toward the outer cortical cell layers in a region defining the incipient nodule. At later stages, MtCLE12 and MtCLE13 were expressed in differentiating nodules and in the apical part of mature, elongated nodules. Functional analysis revealed a putative role for MtCLE12 and MtCLE13 in autoregulation of nodulation, a mechanism that controls the number of nodules and involves systemic signals mediated by a leucine-rich repeat receptor-like kinase, SUNN, which is active in the shoot. When MtCLE12 and MtCLE13 were ectopically expressed in transgenic roots, nodulation was abolished at the level of the nodulation factor signal transduction, and this inhibition involved long-distance signaling. In addition, composite plants with roots ectopically expressing MtCLE12 or MtCLE13 had elongated petioles. This systemic effect was not observed in transgenic roots ectopically expressing MtCLE12 and MtCLE13 in a sunn-1 mutant background, although nodulation was still strongly reduced. These results suggest multiple roles for CLE signaling in nodulation.