The nodule inception‐like protein 7 modulates nitrate sensing and metabolism in Arabidopsis

Abstract

SummaryNitrate is an essential nutrient, and is involved in many adaptive responses of plants, such as localized proliferation of roots, flowering or stomatal movements. How such nitrate-specific mechanisms are regulated at the molecular level is poorly understood. Although the Arabidopsis ANR1 transcription factor appears to control stimulation of lateral root elongation in response to nitrate, no regulators of nitrate assimilation have so far been identified in higher plants. Legume-specific symbiotic nitrogen fixation is under the control of the putative transcription factor, NIN, in Lotus japonicus. Recently, the algal homologue NIT2 was found to regulate nitrate assimilation. Here we report that Arabidopsis thaliana NIN-like protein 7 (NLP7) knockout mutants constitutively show several features of nitrogen-starved plants, and that they are tolerant to drought stress. We show that nlp7 mutants are impaired in transduction of the nitrate signal, and that the NLP7 expression pattern is consistent with a function of NLP7 in the sensing of nitrogen. Translational fusions with GFP showed a nuclear localization for the NLP7 putative transcription factor. We propose NLP7 as an important element of the nitrate signal transduction pathway and as a new regulatory protein specific for nitrogen assimilation in non-nodulating plants.

An RNA Sequencing Transcriptome Analysis Reveals Novel Insights into Molecular Aspects of the Nitrate Impact on the Nodule Activity of Medicago truncatula

“…Up-regulation occurred in the genes for the nitrate transporters of the NRT/peptide transporter protein families 1 and 2 (Forde, 2000;Wang et al, 2012), nitrate and nitrite reductase (Horchani et al, 2011), siroheme synthase, the Numerous Infections and Polyphenolics/ Lateral Root-Organ Defective (NIP/LATD) gene (Bagchi et al, 2012), and a gene involved in the biosynthesis of molybdenum-containing cofactors (Molybdopterin biosynthesis calnexin1; Schwarz et al, 1997). As expected, the gene for the nodule inception protein was downregulated (Castaings et al, 2009 The impact of nitrate on mature nodules proved to be rapid and of a complex nature at the molecular level (Supplemental Tables S2 to S4). The per plant nitrogen fixation was substantially reduced, and strong shifts in metabolism occurred within 1 d of nitrate exposure.…”

Nuclear retention of the transcription factor NLP7 orchestrates the early response to nitrate in plants

“…Thus, it is possible that NLP6 and other NLPs could bind some NLP7 targets and regulate their expression in the absence of NLP7. However, the fact that the nlp7 mutants, but not other nlp mutants, have a clear nitraterelated phenotype 7 supports the hypothesis that NLP7 is the major regulatory element among NLP proteins.…”

“…The two nlp7 allelic knockout mutants, nlp7-1 and nlp7-3, were in the Columbia (Col-8) wt background of Arabidopsis thaliana. The nlp7-1 mutant background was used for complementation by the pNLP7:NLP7-GFP or by p35S:NLP7-GFP constructs 7 . Plants were grown on a 3 mM KNO 3 Confocal imaging.…”

“…Plasmids were obtained from M. Lepetit (pNRT2.1:LUC) 21 and from B. Dubreucq (pACT:LEC2) 40 . The p35S:NLP7 construct was obtained by subcloning into pBS 7 . Protoplasts were co-transfected with the p35S:GUS plasmid (pRTL2-GUS (ref.…”

“…One exception is NIN-Like Protein7 (NLP7), a putative transcription factor that is expressed constitutively and shares homology with NIN (for Nodule INception), an essential protein for nodulation in legumes 10 . Molecular and physiological analyses suggest that NLP7 is involved in plant responses to nitrate 7 . Here we show that, on nitrate supply, NLP7 is retained inside the nucleus to coordinate an early response to the availability of this essential nutrient.…”