The regulatory region controlling the nitrate-responsive expression of a nitrate reductase gene, NIA1, in Arabidopsis

Nitrate Signaling and Its Role in Regulating Flowering Time in Arabidopsis thaliana

Plant growth is coordinated with the availability of nutrients that ensure its development. Nitrate is a major source of nitrogen (N), an essential macronutrient for plant growth. It also acts as a signaling molecule to modulate gene expression, metabolism, and a variety of physiological processes. Recently, it has become evident that the calcium signal appears to be part of the nitrate signaling pathway. New key players have been discovered and described in Arabidopsis thaliana (Arabidopsis). In addition, knowledge of the molecular mechanisms of how N signaling affects growth and development, such as the nitrate control of the flowering process, is increasing rapidly. Here, we review recent advances in the identification of new components involved in nitrate signal transduction, summarize newly identified mechanisms of nitrate signaling-modulated flowering time in Arabidopsis, and suggest emerging concepts and existing open questions that will hopefully be informative for further discoveries.

Polyamines mediate the inhibitory effect of drought stress on nitrogen reallocation and utilization to regulate grain number in wheat

Drought stress poses a serious threat to grain formation in wheat. Nitrogen (N) plays crucial roles in plant organ development; however, the physiological mechanisms by which drought stress affects plant N availability and mediates the formation of grains in spikes of winter wheat are still unclear. In this study, we determined that pre-reproductive drought stress significantly reduced the number of fertile florets and the number of grains formed. Transcriptome analysis demonstrated that this was related to N metabolism, and in particular, the metabolism pathways of arginine (the main precursor for synthesis of polyamine) and proline. Continuous drought stress restricted plant N accumulation and reallocation rates, and plants preferentially allocated more N to spike development. As the activities of amino acid biosynthesis enzymes and catabolic enzymes were inhibited, more free amino acids accumulated in young spikes. The expression of polyamine synthase genes was down-regulated under drought stress, whilst expression of genes encoding catabolic enzymes was enhanced, resulting in reductions in endogenous spermidine and putrescine. Treatment with exogenous spermidine optimized N allocation in young spikes and leaves, which greatly alleviated the drought-induced reduction in the number of grains per spike. Overall, our results show that pre-reproductive drought stress affects wheat grain numbers by regulating N redistribution and polyamine metabolism.

Genome-wide identification and characterization analysis of RWP-RK family genes reveal their role in flowering time of Chrysanthemum lavandulifolium

BACKGROUND

RWP-RKs are plant specific transcription factors, which are widely distributed in plants in the form of polygenic families and play key role in nitrogen absorption and utilization, and are crucial to plant growth and development. However, the genome-wide identification and function of RWP-RK in Compositae plants are widely unknown.

RESULTS

In this study, 101 RWP-RKs in Chrysanthemum lavandulifolium were identified and tandem repeat was an important way for the expansion of RWP-RKs in Compositae species. 101 RWP-RKs contain 38 NIN-like proteins (NLPs) and 31 RWP- RK domain proteins (RKDs), as well as 32 specific expansion members. qRT-PCR results showed that 7 ClNLPs in leaves were up-regulated at the floral transition stage, 10 ClNLPs were negatively regulated by low nitrate conditions, and 3 of them were up-regulated by optimal nitrate conditions. In addition, the flowering time of Chrysanthemum lavandulifolium was advanced under optimal nitrate conditions, the expression level of Cryptochromes (ClCRYs), phytochrome C (ClPHYC) and the floral integration genes GIGANTEA (ClGI), CONSTANS-LIKE (ClCOL1, ClCOL4, ClCOL5), FLOWERING LOCUS T (ClFT), FLOWERING LOCUS C (ClFLC), SUPPRESSOR OF OVER-EXPRESSION OF CONSTANS 1 (ClSOC1) also were up-regulated. The expression level of ClCRY1a, ClCRY1c, ClCRY2a and ClCRY2c in the vegetative growth stage induced by optimal nitrate reached the expression level induced by short-day in the reproductive growth stage, which supplemented the induction effect of short-day on the transcription level of floral-related genes in advance.

CONCLUSIONS

It was speculated that ClNLPs may act on the photoperiodic pathway under optimal nitrate environment, and ultimately regulate the flowering time by up-regulating the transcription level of ClCRYs. These results provide new perspective for exploring the mechanism of nitrate/nitrogen affecting flowering in higher plants.

A molecular framework underlying low-nitrogen-induced early leaf senescence in Arabidopsis thaliana

Nitrogen (N) deficiency causes early leaf senescence, resulting in accelerated whole-plant maturation and severely reduced crop yield. However, the molecular mechanisms underlying N-deficiency-induced early leaf senescence remain unclear, even in the model species Arabidopsis thaliana. In this study, we identified Growth, Development and Splicing 1 (GDS1), a previously reported transcription factor, as a new regulator of nitrate (NO₃^-) signaling by a yeast-one-hybrid screen using a NO₃^- enhancer fragment from the promoter of NRT2.1. We showed that GDS1 promotes NO₃^- signaling, absorption and assimilation by affecting the expression of multiple NO₃^- regulatory genes, including Nitrate Regulatory Gene2 (NRG2). Interestingly, we observed that gds1 mutants show early leaf senescence as well as reduced NO₃^- content and N uptake under N-deficient conditions. Further analyses indicated that GDS1 binds to the promoters of several senescence-related genes, including Phytochrome-Interacting Transcription Factors 4 and 5 (PIF4 and PIF5) and represses their expression. Interestingly, we found that N deficiency decreases GDS1 protein accumulation, and GDS1 could interact with Anaphase Promoting Complex Subunit 10 (APC10). Genetic and biochemical experiments demonstrated that Anaphase Promoting Complex or Cyclosome (APC/C) promotes the ubiquitination and degradation of GDS1 under N deficiency, resulting in loss of PIF4 and PIF5 repression and consequent early leaf senescence. Furthermore, we discovered that overexpression of GDS1 could delay leaf senescence and improve seed yield and N-use efficiency (NUE) in Arabidopsis. In summary, our study uncovers a molecular framework illustrating a new mechanism underlying low-N-induced early leaf senescence and provides potential targets for genetic improvement of crop varieties with increased yield and NUE.

Histone chaperone NUCLEOSOME ASSEMBLY PROTEIN 1 proteins affect plant growth under nitrogen deficient conditions in Arabidopsis thaliana

Nitrogen (N) availability is one of the most important factors regulating plant metabolism and growth as it affects global gene expression profiles. Dynamic changes in chromatin structure, including histone modifications and nucleosome assembly/disassembly, have been extensively shown to regulate gene expression under various environmental stresses in plants. However, the involvement of chromatin related changes in plant nutrient responses has been demonstrated only in a few studies to date. In this study, we investigated the function of histone chaperone NUCLEOSOME ASSEMBLY PROTEIN1 (NAP1) proteins under N deficient conditions in Arabidopsis. In the nap1;1 nap1;2 nap1;3 triple mutant (m123-1), the expression of N-responsive marker genes and growth of lateral roots were decreased under N deficient conditions. In addition, the m123-1 plants showed a delay in N deficiency-induced leaf senescence. Taken together, these results suggest that NAP1s affect plant growth under N deficient conditions in Arabidopsis.

Soybean responds to phosphate starvation through reversible protein phosphorylation

Phosphorus (P) deficiency is considered as a major constraint on crop production. Although a set of adaptative strategies are extensively suggested in soybean (Glycine max) to phosphate (Pi) deprivation, molecular mechanisms underlying reversible protein phosphorylation in soybean responses to P deficiency remains largely unclear. In this study, isobaric tags for relative and absolute quantitation, combined with liquid chromatography and tandem mass spectrometry analysis was performed to identify differential phosphoproteins in soybean roots under Pi sufficient and deficient conditions. A total of 427 phosphoproteins were found to exhibit differential accumulations, with 213 up-regulated and 214 down-regulated. Among them, a nitrate reductase, GmNR4 exhibiting increased phosphorylation levels under low Pi conditions, was further selected to evaluate the effects of phosphorylation on its nitrate reductase activity and subcellular localization. Mutations of GmNR4 phosphorylation levels significantly influenced its activity in vitro, but not for its subcellular localization. Taken together, identification of differential phosphoproteins reveled the complex regulatory pathways for soybean adaptation to Pi starvation through reversible protein phosphorylation.

Tonoplast-Localized OsMOT1;2 Participates in Interorgan Molybdate Distribution in Rice

Molybdenum (Mo) is an essential element for plant growth and is utilized by several key enzymes in biological redox processes. Rice assimilates molybdate ions via OsMOT1;1, a transporter with a high affinity for molybdate. However, other systems involved in the molecular transport of molybdate in rice remain unclear. Here, we characterized OsMOT1;2, which shares amino acid sequence similarity with AtMOT1;2 and functions in vacuolar molybdate export. We isolated a rice mutant harboring a complete deletion of OsMOT1;2. This mutant exhibited a significantly lower grain Mo concentration than the wild type (WT), but its growth was not inhibited. The Mo concentration in grains was restored by the introduction of WT OsMOT1;2. The OsMOT1;2-GFP protein was localized to the vacuolar membrane when transiently expressed in rice protoplasts. At the reproductive growth stage of the WT plant, OsMOT1;2 was highly expressed in the 2nd and lower leaf blades and nodes. The deletion of OsMOT1;2 impaired interorgan Mo allocation in aerial parts: relative to the WT, the mutant exhibited decreased Mo levels in the 1st and 2nd leaf blades and grains but increased Mo levels in the 2nd and lower leaf sheaths, nodes and internodes. When the seedlings were exposed to a solution with a high KNO3 concentration in the absence of Mo, the mutant exhibited significantly lower nitrate reductase activity in the shoots than the WT. Our results suggest that OsMOT1;2 plays an essential role in interorgan Mo distribution and molybdoenzyme activity in rice.

Nitrate-responsive NIN-like protein transcription factors perform unique and redundant roles in Arabidopsis

Upon sensing nitrate, NODULE INCEPTION (NIN)-like protein (NLP) transcription factors alter gene expression to promote nitrate uptake and utilization. Of the nine NLPs in Arabidopsis, the physiological roles of only three NLPs (NLP6-NLP8) have been characterized to date. To evaluate the unique and redundant roles of Arabidopsis NLPs, we assessed the phenotypes of single and higher order nlp mutants. Unlike other nlp single mutants, nlp2 and nlp7 single mutants showed a reduction in shoot fresh weight when grown in the presence of nitrate as the sole nitrogen source, indicating that NLP2, like NLP7, plays a major role in vegetative growth. Interestingly, the growth defect of nlp7 recovered upon the supply of ammonium or glutamine, whereas that of nlp2 did not. Furthermore, complementation assays using chimeric constructs revealed that the coding sequence, but not the promoter region, of NLP genes was responsible for the differences between nlp2 and nlp7 single mutant phenotypes, suggesting differences in protein function. Importantly, nitrate utilization was almost completely abolished in the nlp septuple mutant (nlp2 nlp4 nlp5 nlp6 nlp7 nlp8 nlp9), suggesting that NLPs other than NLP2 and NLP7 also assist in the regulation of nitrate-inducible gene expression and nitrate-dependent promotion of vegetative growth in Arabidopsis.

The NIN-like protein 5 (ZmNLP5) transcription factor is involved in modulating the nitrogen response in maize

Maize exhibits marked growth and yield response to supplemental nitrogen (N). Here, we report the functional characterization of a maize NIN-like protein ZmNLP5 as a central hub in a molecular network associated with N metabolism. Predominantly expressed and accumulated in roots and vascular tissues, ZmNLP5 was shown to rapidly respond to nitrate treatment. Under limited N supply, compared with that of wild-type (WT) seedlings, the zmnlp5 mutant seedlings accumulated less nitrate and nitrite in the root tissues and ammonium in the shoot tissues. The zmnlp5 mutant plants accumulated less nitrogen than the WT plants in the ear leaves and seed kernels. Furthermore, the mutants carrying the transgenic ZmNLP5 cDNA fragment significantly increased the nitrate content in the root tissues compared with that of the zmnlp5 mutants. In the zmnlp5 mutant plants, loss of the ZmNLP5 function led to changes in expression for a significant number of genes involved in N signalling and metabolism. We further show that ZmNLP5 directly regulates the expression of nitrite reductase 1.1 (ZmNIR1.1) by binding to the nitrate-responsive cis-element at the 5' UTR of the gene. Interestingly, a natural loss-of-function allele of ZmNLP5 in Mo17 conferred less N accumulation in the ear leaves and seed kernels resembling that of the zmnlp5 mutant plants. Our findings show that ZmNLP5 is involved in mediating the plant response to N in maize.

Exploring the Potential of Overexpressed OsCIPK2 Rice as a Nitrogen Utilization Efficient Crop and Analysis of Its Associated Rhizo-Compartmental Microbial Communities

Nitrogen (N) is one of the indispensable factors in rice growth and development. China holds a premier position in the production of rice and at the same time also faces higher N fertilizer costs along with serious damage to the environment. A better solution is much needed to address these issues, without disrupting the production of rice as an important cereal, while minimizing all the deleterious effects on the environment. Two isogenic lines Kitaake (WT) and its genetically modified line CIPK2 (RC), overexpressing the gene for Calcineurin B-like interacting protein kinase 2 (OsCIPK2) with better nitrogen use efficiency (NUE), were compared for their growth and development under low versus normal levels of N. NUE is a complex trait mainly related to a plant’s efficiency in extraction, assimilation, and recycling of N from soil. The microbial population was analyzed using high-throughput Illumina Miseq 16S rRNA sequencing and found that RC with CIPK2, specifically expressed in rice root, not only performed better without nitrogen fertilizer (LN) but also increased the diversity of bacterial communities in rice rhizosphere compartments (rhizosphere, rhizoplane, and endosphere). The relative abundance of beneficial bacteria phyla increased, which are known to promote the circulation and transformation of N in rhizosphere soil. To further explore the potential of RC regarding better performance under LN, the ion fluxes in root apical were detected by non-invasive micro-test technique (NMT). We found that RC can absorb more Ca²⁺ and NO₃⁻ under LN as compared to WT. Finally, compared to WT, RC plants exhibited better growth of root and shoot, and increased yield and N uptake under LN, whereas there was no significant difference in the growth of two rice lines under normal nitrogen (NN) treatment. We are able to get preliminary results, dealing with the OsCIPK2 overexpressed rice line, by studying the rice molecular, physiological, and chemical parameters related to NUE. The results laid the foundation for further research on N absorption and utilization in rice from the soil and the interaction with microbial communities.

Identification of transcription factors of nitrate reductase gene promoters and NRE2 cis-element through yeast one-hybrid screening in Nicotiana tabacum

BACKGROUND

This study aimed to identify the transcription factors of nitrate reductase genes (NIA1 and NIA2) promoters and hypothetical cis-element of NRE2. Based on the constructed cDNA library of Nicotiana tabacum K326, a yeast one-hybrid system was established using the Matchmaker® Gold Yeast One-Hybrid Library Screening System from Clontech. The transcription factors of NIA1 andNIA2 promoters and NRE2 cis-elements were screened.

RESULTS

After sequencing and bioinformatics analysis, 15 cDNA sequences were identified: 9 for NIA1 (including XP_016503563.1 and NP_001312236.1), 3 for NIA2 (including XP_016510250.1), and 3 for NRE2 (including XM_016576899.1). XP_016503563.1 was annotated in PREDICTED: CRM-domain containing factor CFM3, and NP_001312236.1chloroplastic/mitochondrial-like in Nicotiana tabacum. NP_001312236.1 was annotated in Sulfite oxidase-like of Nicotiana tabacum. XP_016510250.1 was annotated as PREDICTED: uncharacterized protein LOC107827596 in Nicotiana tabacum. XM_016576899.1 was annotated in PREDICTED: Nicotiana tabacum RING-H2 finger protein ATL16-like (LOC107759033).

CONCLUSION

A yeast one-hybrid library was successfully constructed. The identified transcription factors may provide a theoretical basis for the study of plant nitrate reductase.

Integrated bioinformatics analysis of As, Au, Cd, Pb and Cu heavy metal responsive marker genes through Arabidopsis thaliana GEO datasets

BACKGROUND

Current environmental pollution factors, particularly the distribution and diffusion of heavy metals in soil and water, are a high risk to local environments and humans. Despite striking advances in methods to detect contaminants by a variety of chemical and physical solutions, these methods have inherent limitations such as small dimensions and very low coverage. Therefore, identifying novel contaminant biomarkers are urgently needed.

METHODS

To better track heavy metal contaminations in soil and water, integrated bioinformatics analysis to identify biomarkers of relevant heavy metal, such as As, Cd, Pb and Cu, is a suitable method for long-term and large-scale surveys of such heavy metal pollutants. Subsequently, the accuracy and stability of the results screened were experimentally validated by quantitative PCR experiment.

RESULTS

We obtained 168 differentially expressed genes (DEGs) which contained 59 up-regulated genes and 109 down-regulated genes through comparative bioinformatics analyses. Subsequently, the gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichments of these DEGs were performed, respectively. GO analyses found that these DEGs were mainly related to responses to chemicals, responses to stimulus, responses to stress, responses to abiotic stimulus, and so on. KEGG pathway analyses of DEGs were mainly involved in the protein degradation process and other biologic process, such as the phenylpropanoid biosynthesis pathways and nitrogen metabolism. Moreover, we also speculated that nine candidate core biomarker genes (namely, NILR1, PGPS1, WRKY33, BCS1, AR781, CYP81D8, NR1, EAP1 and MYB15) might be tightly correlated with the response or transport of heavy metals. Finally, experimental results displayed that these genes had the same expression trend response to different stresses as mentioned above (Cd, Pb and Cu) and no mentioned above (Zn and Cr).

CONCLUSION

In general, the identified biomarker genes could help us understand the potential molecular mechanisms or signaling pathways responsive to heavy metal stress in plants, and could be applied as marker genes to track heavy metal pollution in soil and water through detecting their expression in plants growing in those environments.

The role of protein-protein interactions mediated by the PB1 domain of NLP transcription factors in nitrate-inducible gene expression

BACKGROUND

NIN-LIKE PROTEIN (NLP) transcription factors are master regulators of nitrate-inducible gene expression in higher plants. NLP transcription factors contain a nitrate signal-responsive domain in the amino-terminal region, an RWP-RK-type DNA-binding domain in the middle, and a Phox and Bem1 (PB1) domain at the carboxy terminus. Although the PB1 domain of NLP transcription factors appears to mediate protein-protein interactions associated with nitrate-inducible gene expression in higher plants, its precise role in nitrate-inducible gene expression has not previously been characterized.

RESULTS

Yeast two-hybrid assays with the PB1 domain of the Arabidopsis transcription factor NLP7 revealed NLP-NLP interactions that required the core amino acid residues (K867, D909, D911, and E913) within the PB1 domain. Consistent with previous speculation on redundant and overlapping functions between different Arabidopsis NLP transcription factors, NLP-NLP interactions were observed between a variety of combinations of different NLP transcription factors. Furthermore, a mutated form of NLP7 that harbored amino acid substitutions at K867, D909, D911, and E913 required a far higher level of expression than wild-type NLP7 to restore nitrate-responsive gene expression and growth of nlp6 nlp7-1 double mutants. Surprisingly, however, the ability to transactivate nitrate-responsive promoters in protoplast transient expression assays was similar between wild-type and mutant forms of NLP7, suggesting that the PB1 domain was not required for transcription from naked DNA.

CONCLUSIONS

Protein-protein interactions mediated by the PB1 domain of NLP transcription factors are necessary for full induction of nitrate-dependent expression of target genes in planta. The PB1 domains of NLP transcription factors may act on gene expression from chromosomal DNA via homo- and hetero-oligomerization in the presence of nitrate.

Protein Phosphatase (PP2C9) Induces Protein Expression Differentially to Mediate Nitrogen Utilization Efficiency in Rice under Nitrogen-Deficient Condition

Nitrogen (N) is an essential element usually limiting in plant growth and a basic factor for increasing the input cost in agriculture. To ensure the food security and environmental sustainability it is urgently required to manage the N fertilizer. The identification or development of genotypes with high nitrogen utilization efficiency (NUE) which can grow efficiently and sustain yield in low N conditions is a possible solution. In this study, two isogenic rice genotypes i.e., wild-type rice kitaake and its transgenic line PP2C9TL overexpressed protein phosphatase gene (PP2C9) were used for comparative proteomics analysis at control and low level of N to identify specific proteins and encoding genes related to high NUE. 2D gel electrophoresis was used to perform the differential proteome analysis. In the leaf proteome, 30 protein spots were differentially expressed between the two isogenic lines under low N level which were involved in the process of energy, photosynthesis, N metabolism, signaling, and defense mechanisms. In addition, we have found that protein phosphatase enhances nitrate reductase activation by downregulation of SnRK1 and 14-3-3 proteins. Furthermore, we showed that PP2C9TL exhibits higher NUE than WT due to higher activity of nitrate reductase. This study provides new insights on the rice proteome which would be useful in the development of new strategies to increase NUE in cereal crops.

Genome-Wide Identification and Characterization of NODULE-INCEPTION-Like Protein (NLP) Family Genes in Brassica napus

NODULE-INCEPTION-like proteins (NLPs) are conserved, plant-specific transcription factors that play crucial roles in responses to nitrogen deficiency. However, the evolutionary relationships and characteristics of NLP family genes in Brassica napus are unclear. In this study, we identified 31 NLP genes in B. napus, including 16 genes located in the A subgenome and 15 in the C subgenome. Subcellular localization predictions indicated that most BnaNLP proteins are localized to the nucleus. Phylogenetic analysis suggested that the NLP gene family could be divided into three groups and that at least three ancient copies of NLP genes existed in the ancestor of both monocots and dicots prior to their divergence. The ancestor of group III NLP genes may have experienced duplication more than once in the Brassicaceae species. Three-dimensional structural analysis suggested that 14 amino acids in BnaNLP7-1 protein are involved in DNA binding, whereas no binding sites were identified in the two RWP-RK and PB1 domains conserved in BnaNLP proteins. Expression profile analysis indicated that BnaNLP genes are expressed in most organs but tend to be highly expressed in a single organ. For example, BnaNLP6 subfamily members are primarily expressed in roots, while the four BnaNLP7 subfamily members are highly expressed in leaves. BnaNLP genes also showed different expression patterns in response to nitrogen-deficient conditions. Under nitrogen deficiency, all members of the BnaNLP1/4/5/9 subfamilies were upregulated, all BnaNLP2/6 subfamily members were downregulated, and BnaNLP7/8 subfamily members showed various expression patterns in different organs. These results provide a comprehensive evolutionary history of NLP genes in B. napus, and insight into the biological functions of BnaNLP genes in response to nitrogen deficiency.

Nitrate Reductases Are Relocalized to the Nucleus by AtSIZ1 and Their Levels Are Negatively Regulated by COP1 and Ammonium

Nitrate reductases (NRs) catalyze the first step in the reduction of nitrate to ammonium. NR activity is regulated by sumoylation through the E3 ligase activity of AtSIZ1. However, it is not clear how NRs interact with AtSIZ1 in the cell, or how nitrogen sources affect NR levels and their cellular localization. Here, we show that the subcellular localization of NRs is modulated by the E3 SUMO (Small ubiquitin-related modifier) ligase AtSIZ1 and that NR protein levels are regulated by nitrogen sources. Transient expression analysis of GFP fusion proteins in onion epidermal cells showed that the NRs NIA1 and NIA2 localize to the cytoplasmic membrane, and that AtSIZ1 localizes to the nucleoplasm, including nuclear bodies, when expressed separately, whereas NRs and AtSIZ1 localize to the nucleus when co-expressed. Nitrate did not affect the subcellular localization of the NRs, but it caused AtSIZ1 to move from the nucleus to the cytoplasm. NRs were not detected in ammonium-treated cells, whereas the localization of AtSIZ1 was not altered by ammonium treatment. NR protein levels increased in response to nitrate but decreased in response to ammonium. In addition, NR protein levels increased in response to a 26S proteasome inhibitor and in cop1-4 and DN-COP1-overexpressing transgenic plants. NR protein degradation occurred later in cop1-4 than in the wild-type, although the NR proteins did not interact with COP1. Therefore, AtSIZ1 controls nuclear localization of NR proteins, and ammonium negatively regulates their levels. The function and stability of NR proteins might be post-translationally modulated by ubiquitination.

Enhanced photosynthetic capacity increases nitrogen metabolism through the coordinated regulation of carbon and nitrogen assimilation in Arabidopsis thaliana

Plant growth and productivity depend on interactions between the metabolism of carbon and nitrogen. The sensing ability of internal carbon and nitrogen metabolites (the C/N balance) enables plants to regulate metabolism and development. In order to investigate the effects of an enhanced photosynthetic capacity on the metabolism of carbon and nitrogen in photosynthetically active tissus (source leaves), we herein generated transgenic Arabidopsis thaliana plants (ApFS) that expressed cyanobacterial fructose-1,6-/sedoheptulose-1,7-bisphosphatase in their chloroplasts. The phenotype of ApFS plants was indistinguishable from that of wild-type plants at the immature stage. However, as plants matured, the growth of ApFS plants was superior to that of wild-type plants. Starch levels were higher in ApFS plants than in wild-type plants at 2 and 5 weeks. Sucrose levels were also higher in ApFS plants than in wild-type plants, but only at 5 weeks. On the other hand, the contents of various free amino acids were lower in ApFS plants than in wild-type plants at 2 weeks, but were similar at 5 weeks. The total C/N ratio was the same in ApFS plants and wild-type plants, whereas nitrite levels increased in parallel with elevations in nitrate reductase activity at 5 weeks in ApFS plants. These results suggest that increases in the contents of photosynthetic intermediates at the early growth stage caused a temporary imbalance in the free-C/free-N ratio and, thus, the feedback inhibition of the expression of genes involved in the Calvin cycle and induction of the expression of those involved in nitrogen metabolism due to supply deficient free amino acids for maintenance of the C/N balance in source leaves of ApFS plants.

Simple Spectroscopic Determination of Nitrate, Nitrite, and Ammonium in Arabidopsis thaliana

Plants use nitrate, nitrite, and ammonium as inorganic nitrogen (N) sources. These N compounds are included in plant tissues at various concentrations depending on the balance between their uptake and assimilation. Thus, the contents of nitrate, nitrite, and ammonium are physiological indicators of plant N economy. Here, we describe a protocol for measurement of these inorganic N species in A. thaliana shoots or roots.

Seed Biology Updates - Highlights and New Discoveries in Seed Dormancy and Germination Research

An understanding of the biology of seeds has been greatly advanced in recent years. The progresses, particularly in the field of seed dormancy and germination research, have been made at a remarkable speed. Some of the possible epigenetic mechanisms, including an involvement of non-coding RNA, which were predicted for DELAY OF GERMINATION1 just a few years ago, have now been demonstrated with strong molecular and genetic evidence. Imprinting, or parent-of-origin-specific gene silencing/expression, which was characterized particularly for developing seeds, was also found in imbibed seeds and suggested for dormancy mechanisms. Hormone biology in seeds, which is the most advanced and almost a traditional area of seed research, also presents a new dimension. Upstream regulators of hormone metabolism and hormone transporters, such as abscisic acid and gibberellin influx/efflux carriers, have been identified. Characterization of the novel posttranslational modification pathways, including the N-end rule and S-nitrosylation pathways, which play a critical role in turnover of the major hormone signal transduction proteins, also expanded our knowledge about the complexity of hormone signaling in seeds. These progresses made at the molecular level are significant steps toward a better understanding of how seeds translate soil and other environmental signals into their internal hormone biology and make an important decision to stay dormant or commence with germination.

Arabidopsis Root-Type Ferredoxin:NADP(H) Oxidoreductase 2 is Involved in Detoxification of Nitrite in Roots

Ferredoxin:NADP(H) oxidoreductase (FNR) plays a key role in redox metabolism in plastids. Whereas leaf FNR (LFNR) is required for photosynthesis, root FNR (RFNR) is believed to provide electrons to ferredoxin (Fd)-dependent enzymes, including nitrite reductase (NiR) and Fd-glutamine-oxoglutarate aminotransferase (Fd-GOGAT) in non-photosynthetic conditions. In some herbal species, however, most nitrate reductase activity is located in photosynthetic organs, and ammonium in roots is assimilated mainly by Fd-independent NADH-GOGAT. Therefore, RFNR might have a limited impact on N assimilation in roots grown with nitrate or ammonium nitrogen sources. AtRFNR genes are rapidly induced by application of toxic nitrite. Thus, we tested the hypothesis that RFNR could contribute to nitrite reduction in roots by comparing Arabidopsis thaliana seedlings of the wild type with loss-of-function mutants of RFNR2 When these seedlings were grown under nitrate, nitrite or ammonium, only nitrite nutrition caused impaired growth and nitrite accumulation in roots of rfnr2 Supplementation of nitrite with nitrate or ammonium as N sources did not restore the root growth in rfnr2 Also, a scavenger for nitric oxide (NO) could not effectively rescue the growth impairment. Thus, nitrite toxicity, rather than N depletion or nitrite-dependent NO production, probably causes the rfnr2 root growth defect. Our results strongly suggest that RFNR2 has a major role in reduction of toxic nitrite in roots. A specific set of genes related to nitrite reduction and the supply of reducing power responded to nitrite concomitantly, suggesting that the products of these genes act co-operatively with RFNR2 to reduce nitrite in roots.

Separate elements of the TERMINAL FLOWER 1 cis-regulatory region integrate pathways to control flowering time and shoot meristem identity

TERMINAL FLOWER 1 (TFL1) is a key regulator of Arabidopsis plant architecture, which responds to developmental and environmental signals to control flowering time and the fate of shoot meristems. TFL1 expression pattern is dynamic, being found in all shoot meristems, but not in floral meristems, with its level and distribution changing throughout development. Using a variety of experimental approaches, we have analysed the TFL1 promoter to elucidate its functional structure. TFL1 expression is based on distinct cis-regulatory regions, the most important ones located 3' of the coding sequence. Our results indicate that TFL1 expression in the shoot apical vs. lateral inflorescence meristems is controlled through distinct cis-regulatory elements, suggesting that different signals control expression in these meristem types. Moreover, we identified a cis-regulatory region necessary for TFL1 expression in the vegetative shoot, required for a wild-type flowering time, supporting that TFL1 expression in the vegetative meristem controls flowering time. Our study provides a model for the functional organization of TFL1 cis-regulatory regions, contributing to understanding of how developmental pathways are integrated at the genomic level of a key regulator to control plant architecture.

Transcriptional networks in the nitrate response of Arabidopsis thaliana

Nitrogen is an essential macronutrient for plants and its availability is a key determinant of plant growth and development and crop yield. Besides their nutritional role, N nutrients and metabolites are signals that activate signaling pathways that modulate many plant processes. Because the most abundant inorganic N source for plants in agronomic soils is nitrate, much of the work to understand plant N-signaling has focused on this nutrient. Over the last years, several studies defined a comprehensive catalog of nitrate-responsive genes, involved in nitrate transport, metabolism and a variety of other processes. Despite significant progress in recent years, primarily using Arabidopsis thaliana as a model system, the molecular mechanisms by which nitrate elicits changes in transcript abundance are still not fully understood. Here we highlight recent advancements in identifying key transcription factors and transcriptional mechanisms that orchestrate the gene expression response to changes in nitrate availability in A. thaliana.

Transgenic poplar expressing the pine GS1a show alterations in nitrogen homeostasis during drought

Transgenic hybrid poplars engineered to express ectopically the heterologous pine cytosolic GS1a display a number of significant pleiotropic phenotypes including enhanced growth, enhanced nitrogen use efficiency, and resistance to drought stress. The present study was undertaken in order to assess mechanisms whereby ectopic expression of pine GS1a in transgenic poplars results in enhanced agronomic phenotypes. Microarray analysis using the Agilent Populus whole genome array has allowed identification of genes differentially expressed between wild type (WT) and GS transgenics in four tissues (sink leaves, source leaves, stems, and roots) under three growth conditions (well-watered, drought, and recovery). Analysis revealed that differentially expressed genes in functional categories related to nitrogen metabolism show a trend of significant down-regulation in GS poplars compared to the WT, including genes encoding nitrate and nitrite reductases. The down-regulation of these genes was verified using qPCR, and downstream effects were further tested using NR activity assays. Results suggest that higher glutamine levels in GS transgenics regulate nitrate uptake and reduction. Transcript levels of nitrogen-related genes in leaves, including GS/GOGAT cycle enzymes, aspartate aminotransferase, GABA shunt enzymes, photorespiration enzymes, asparagine synthetase, phenylalanine ammonia lyase, isocitrate dehydrogenase, and PII, were also assessed using qPCR revealing significant differences between GS poplars and the WT. Moreover, metabolites related to these differentially expressed genes showed alterations in levels, including higher levels of GABA, hydroxyproline, and putrescine in the GS transgenic. These alterations in nitrogen homeostasis offer insights into mechanisms accounting for drought tolerance observed in GS poplars.

Transcription factors involved in controlling the expression of nitrate reductase genes in higher plants

Nitrate reductase is a key enzyme in nitrogen assimilation, and it catalyzes the nitrate-to-nitrite reduction process in plants. A variety of factors, including nitrate, light, metabolites, phytohormones, low temperature, and drought, modulate the expression levels of nitrate reductase genes as well as nitrate reductase activity, which is consistent with its physiological role. Recently, several transcription factors involved in controlling the expression of nitrate reductase genes have been identified in Arabidopsis. NODULE-INCEPTION-like proteins (NLPs) are transcription factors responsible for nitrate-inducible expression of nitrate reductase genes. Since NLPs also control nitrate-inducible expression of genes encoding nitrate transporter, nitrite transporter, and nitrite reductase, the expression levels of nitrate reduction pathway-associated genes are coordinately modulated by NLPs in response to nitrate. LATERAL ORGAN BOUNDARIES DOMAIN (LBD) transcription factors (LBD37-LBD39) are strong candidates for transcription factors mediating negative feedback regulation in response to increases in the contents of nitrogen-containing metabolites, whereas LONG HYPOCOTYL 5 (HY5) that promotes photomorphogenesis in light may be a transcription factor involved in light-induced expression of a nitrate reductase gene. Furthermore, unidentified transcription factors likely mediate other signals and regulate the expression of nitrate reductase genes. This review presents a summary of our current knowledge of such transcription factors.

Nitrate foraging by Arabidopsis roots is mediated by the transcription factor TCP20 through the systemic signaling pathway

To compete for nutrients in diverse soil microenvironments, plants proliferate lateral roots preferentially in nutrient-rich zones. For nitrate, root foraging involves local and systemic signaling; however, little is known about the genes that function in the systemic signaling pathway. By using nitrate enhancer DNA to screen a library of Arabidopsis transcription factors in the yeast one-hybrid system, the transcription factor gene TEOSINTE BRANCHED1/CYCLOIDEA/PROLIFERATING CELL FACTOR1-20 (TCP20) was identified. TCP20, which belongs to an ancient, plant-specific gene family that regulates shoot, flower, and embryo development, was implicated in nitrate signaling by its ability to bind DNA in more than 100 nitrate-regulated genes. Analysis of insertion mutants of TCP20 showed that they had normal primary and lateral root growth on homogenous nitrate media but were impaired in preferential lateral root growth (root foraging) on heterogeneous media in split-root plates. Inhibition of preferential lateral root growth was still evident in the mutants even when ammonium was uniformly present in the media, indicating that the TCP20 response was to nitrate. Comparison of tcp20 mutants with those of nlp7 mutants, which are defective in local control of root growth but not in the root-foraging response, indicated that TCP20 function is independent of and distinct from NLP7 function. Further analysis showed that tcp20 mutants lack systemic control of root growth regardless of the local nitrate concentrations. These results indicate that TCP20 plays a key role in the systemic signaling pathway that directs nitrate foraging by Arabidopsis roots.

The plant RWP-RK transcription factors: key regulators of nitrogen responses and of gametophyte development

The plant specific RWP-RK family of transcription factors, initially identified in legumes and Chlamydomonas, are found in all vascular plants, green algae, and slime molds. These proteins possess a characteristic RWP-RK motif, which mediates DNA binding. Based on phylogenetic and domain analyses, we classified the RWP-RK proteins of six different species in two subfamilies: the NIN-like proteins (NLPs), which carry an additional PB1 domain at their C-terminus, and the RWP-RK domain proteins (RKDs), which are divided into three subgroups. Although, the functional analysis of this family is still in its infancy, several RWP-RK proteins have a key role in regulating responses to nitrogen availability. The nodulation-specific NIN proteins are involved in nodule organogenesis and rhizobial infection under nitrogen starvation conditions. Arabidopsis NLP7 in particular is a major player in the primary nitrate response. Several RKDs act as transcription factors involved in egg cell specification and differentiation or gametogenesis in algae, the latter modulated by nitrogen availability. Further studies are required to extend the general picture of the functional role of these exciting transcription factors.

Emergence of a new step towards understanding the molecular mechanisms underlying nitrate-regulated gene expression

Nitrogen is one of the primary macronutrients of plants, and nitrate is the most abundant inorganic form of nitrogen in soils. Plants take up nitrate in soils and utilize it both for nitrogen assimilation and as a signalling molecule. Thus, an essential role for nitrate in plants is triggering changes in gene expression patterns, including immediate induction of the expression of genes involved in nitrate transport and assimilation, as well as several transcription factor genes and genes related to carbon metabolism and cytokinin biosynthesis and response. Significant progress has been made in recent years towards understanding the molecular mechanisms underlying nitrate-regulated gene expression in higher plants; a new stage in our understanding of this process is emerging. A key finding is the identification of NIN-like proteins (NLPs) as transcription factors governing nitrate-inducible gene expression. NLPs bind to nitrate-responsive DNA elements (NREs) located at nitrate-inducible gene loci and activate their NRE-dependent expression. Importantly, post-translational regulation of NLP activity by nitrate signalling was strongly suggested to be a vital process in NLP-mediated transcriptional activation and subsequent nitrate responses. We present an overview of the current knowledge of the molecular mechanisms underlying nitrate-regulated gene expression in higher plants.

Nitrate transport and signalling in Arabidopsis

Plants have developed adaptive responses allowing them to cope with nitrogen (N) fluctuation in the soil and maintain growth despite changes in external N availability. Nitrate is the most important N form in temperate soils. Nitrate uptake by roots and its transport at the whole-plant level involves a large panoply of transporters and impacts plant performance. Four families of nitrate-transporting proteins have been identified so far: nitrate transporter 1/peptide transporter family (NPF), nitrate transporter 2 family (NRT2), the chloride channel family (CLC), and slow anion channel-associated homologues (SLAC/SLAH). Nitrate transporters are also involved in the sensing of nitrate. It is now well established that plants are able to sense external nitrate availability, and hence that nitrate also acts as a signal molecule that regulates many aspects of plant intake, metabolism, and gene expression. This review will focus on a global picture of the nitrate transporters so far identified and the recent advances in the molecular knowledge of the so-called primary nitrate response, the rapid regulation of gene expression in response to nitrate. The recent discovery of the NIN-like proteins as master regulators for nitrate signalling has led to a new understanding of the regulation cascade.

Nitrogen-dependent regulation of de novo cytokinin biosynthesis in rice: the role of glutamine metabolism as an additional signal

Cytokinin activity in plants is closely related to nitrogen availability, and an Arabidopsis gene for adenosine phosphate-isopentenyltransferase (IPT), IPT3, is regulated by inorganic nitrogen sources in a nitrate-specific manner. In this study, we have identified another regulatory system of cytokinin de novo biosynthesis in response to nitrogen status. In rice, OsIPT4, OsIPT5, OsIPT7 and OsIPT8 were up-regulated in response to exogenously applied nitrate and ammonium, with accompanying accumulation of cytokinins. Pre-treatment of roots with l-methionine sulfoximine, a potent inhibitor of glutamine synthetase, abolished the nitrate- and ammonium-dependent induction of OsIPT4 and OsIPT5, while glutamine application induced their expression. Thus, neither nitrate nor ammonium, but glutamine or a related metabolite, is essential for the induction of these IPT genes in rice. On the other hand, glutamine-dependent induction of IPT3 occurs in Arabidopsis, at least to some extent. In transgenic lines repressing the expression of OsIPT4, which is the dominant IPT in rice roots, the nitrogen-dependent increase of cytokinin in the xylem sap was significantly reduced, and seedling shoot growth was retarded despite sufficient nitrogen. We conclude that plants possess multiple regulation systems for nitrogen-dependent cytokinin biosynthesis to modulate growth in response to nitrogen availability.

Arabidopsis NIN-like transcription factors have a central role in nitrate signalling

In plants, nitrate is not only a major nitrogen source but also a signalling molecule that modulates the expression of a wide range of genes and that regulates growth and development. The critical role of nitrate as a signalling molecule has been established for several decades. However, the molecular mechanisms underlying the nitrate response have remained elusive, as the transcription factor that primarily responds to nitrate signals has not yet been identified. Here we show that Arabidopsis NIN-LIKE PROTEIN (NLP) family proteins bind the nitrate-responsive cis-element and activate nitrate-responsive cis-element-dependent and nitrate-responsive transcription. Our results also suggest that the activity of NLPs is post-translationally modulated by nitrate signalling. Furthermore, the suppression of NLP function impairs the nitrate-inducible expression of a number of genes and causes severe growth inhibition. These results indicate that NLPs are the transcription factors mediating the nitrate signal and thereby function as master regulators of the nitrate response.

The evolutionary events necessary for the emergence of symbiotic nitrogen fixation in legumes may involve a loss of nitrate responsiveness of the NIN transcription factor

NODULE INCEPTION (NIN) is a key regulator of the symbiotic nitrogen fixation pathway in legumes including Lotus japonicus. NIN-like proteins (NLPs), which are presumably present in all land plants, were recently identified as key transcription factors in nitrate signaling and responses in Arabidopsis thaliana, a non-leguminous plant. Here we show that both NIN and NLP1 of L. japonicus (LjNLP1) can bind to the nitrate-responsive cis-element (NRE) and promote transcription from an NRE-containing promoter as did the NLPs of A. thaliana (AtNLPs). However, differing from LjNLP1 and the AtNLPs that are activated by nitrate signaling through their N-terminal regions, the N-terminal region of NIN did not respond to nitrate. Thus, in the course of the evolution of NIN into a transcription factor that functions in nodulation in legumes, some mutations might arise that converted it to a nitrate-insensitive transcription factor. Because nodule formation is induced under nitrogen-deficient conditions, we speculate that the loss of the nitrate-responsiveness of NIN may be one of the evolutionary events necessary for the emergence of symbiotic nitrogen fixation in legumes.

The evolutionary events necessary for the emergence of symbiotic nitrogen fixation in legumes may involve a loss of nitrate responsiveness of the NIN transcription factor

NODULE INCEPTION (NIN) is a key regulator of the symbiotic nitrogen fixation pathway in legumes including Lotus japonicus. NIN-like proteins (NLPs), which are presumably present in all land plants, were recently identified as key transcription factors in nitrate signaling and responses in Arabidopsis thaliana, a non-leguminous plant. Here we show that both NIN and NLP1 of L. japonicus (LjNLP1) can bind to the nitrate-responsive cis-element (NRE) and promote transcription from an NRE-containing promoter as did the NLPs of A. thaliana (AtNLPs). However, differing from LjNLP1 and the AtNLPs that are activated by nitrate signaling through their N-terminal regions, the N-terminal region of NIN did not respond to nitrate. Thus, in the course of the evolution of NIN into a transcription factor that functions in nodulation in legumes, some mutations might arise that converted it to a nitrate-insensitive transcription factor. Because nodule formation is induced under nitrogen-deficient conditions, we speculate that the loss of the nitrate-responsiveness of NIN may be one of the evolutionary events necessary for the emergence of symbiotic nitrogen fixation in legumes.

Nitrogen transporter and assimilation genes exhibit developmental stage-selective expression in maize (Zea mays L.) associated with distinct cis-acting promoter motifs

Nitrogen is considered the most limiting nutrient for maize (Zea mays L.), but there is limited understanding of the regulation of nitrogen-related genes during maize development. An Affymetrix 82K maize array was used to analyze the expression of ≤ 46 unique nitrogen uptake and assimilation probes in 50 maize tissues from seedling emergence to 31 d after pollination. Four nitrogen-related expression clusters were identified in roots and shoots corresponding to, or overlapping, juvenile, adult, and reproductive phases of development. Quantitative real time PCR data was consistent with the existence of these distinct expression clusters. Promoters corresponding to each cluster were screened for over-represented cis-acting elements. The 8-bp distal motif of the Arabidopsis 43-bp nitrogen response element (NRE) was over-represented in nitrogen-related maize gene promoters. This conserved motif, referred to here as NRE43-d8, was previously shown to be critical for nitrate-activated transcription of nitrate reductase (NIA1) and nitrite reductase (NIR1) by the NIN-LIKE PROTEIN 6 (NLP6) in Arabidopsis. Here, NRE43-d8 was over-represented in the promoters of maize nitrate and ammonium transporter genes, specifically those that showed peak expression during early-stage vegetative development. This result predicts an expansion of the NRE-NLP6 regulon and suggests that it may have a developmental component in maize. We also report leaf expression of putative orthologs of nitrite transporters (NiTR1), a transporter not previously reported in maize. We conclude by discussing how each of the four transcriptional modules may be responsible for the different nitrogen uptake and assimilation requirements of leaves and roots at different stages of maize development.

Post-translational control of nitrate reductase activity responding to light and photosynthesis evolved already in the early vascular plants

Regulation of nitrate reductase (NR) by reversible phosphorylation at a conserved motif is well established in higher plants, and enables regulation of NR in response to rapid fluctuations in light intensity. This regulation is not conserved in algae NR, and we wished to test the evolutionary origin of the regulatory mechanism by physiological examination of ancient land plants. Especially a member of the lycophytes is of interest since their NR is candidate for regulation by reversible phosphorylation based on sequence analysis. We compared Selaginella kraussiana, a member of the lycophytes and earliest vascular plants, with the angiosperm Arabidopsis thaliana, and also tested the moss Physcomitrella patens. Interestingly, optimization of assay conditions revealed that S. kraussiana NR used NADH as an electron donor like A. thaliana, whereas P. patens NR activity depended on NADPH. Examination of light/darkness effects showed that S. kraussiana NR was rapidly regulated similar to A. thaliana NR when a differential (Mg(2+) contra EDTA) assay was used to reveal activity state of NR. This implies that already existing NR enzyme was post-translationally activated by light in both species. Light had a positive effect also on de novo synthesis of NR in S. kraussiana, which could be shown after the plants had been exposed to a prolonged dark period (7 days). Daily variations in NR activity were mainly caused by post-translational modifications. As for angiosperms, the post-translational light activation of NR in S. kraussiana was inhibited by 3-(3,4-dichlorophenyl)-1*1-dimethylurea (DCMU), an inhibitor of photosynthesis and stomata opening. Evolutionary, a post-translational control mechanism for NR have occurred before or in parallel with development of vascular tissue in land plants, and appears to be part of a complex mechanisms for coordination of CO2 and nitrogen metabolism in these plants.

Nitric oxide-mediated maintenance of redox homeostasis contributes to NPR1-dependent plant innate immunity triggered by lipopolysaccharides

The perception of lipopolysaccharides (LPS) by plant cells can lead to nitric oxide (NO) production and defense gene induction. However, the signaling cascades underlying these cellular responses have not yet been resolved. This work investigated the biosynthetic origin of NO and the role of NONEXPRESSOR OF PATHOGENESIS-RELATED GENES1 (NPR1) to gain insight into the mechanism involved in LPS-induced resistance of Arabidopsis (Arabidopsis thaliana). Analysis of inhibitors and mutants showed that LPS-induced NO synthesis was mainly mediated by an arginine-utilizing source of NO generation. Furthermore, LPS-induced NO caused transcript accumulation of alternative oxidase genes and increased antioxidant enzyme activity, which enhanced antioxidant capacity and modulated redox state. We also analyzed the subcellular localization of NPR1 to identify the mechanism for protein-modulated plant innate immunity triggered by LPS. LPS-activated defense responses, including callose deposition and defense-related gene expression, were found to be regulated through an NPR1-dependent pathway. In summary, a significant NO synthesis induced by LPS contributes to the LPS-induced defense responses by up-regulation of defense genes and modulation of cellular redox state. Moreover, NPR1 plays an important role in LPS-triggered plant innate immunity.

Microarray analysis revealed upregulation of nitrate reductase in juvenile cuttings of Eucalyptus grandis, which correlated with increased nitric oxide production and adventitious root formation

The loss of rooting capability following the transition from the juvenile to the mature phase is a known phenomenon in woody plant development. Eucalyptus grandis was used here as a model system to study the differences in gene expression between juvenile and mature cuttings. RNA was prepared from the base of the two types of cuttings before root induction and hybridized to a DNA microarray of E. grandis. In juvenile cuttings, 363 transcripts were specifically upregulated, enriched in enzymes of oxidation/reduction processes. In mature cuttings, 245 transcripts were specifically upregulated, enriched in transcription factors involved in the regulation of secondary metabolites. A gene encoding for nitrate reductase (NIA), which is involved in nitric oxide (NO) production, was among the genes that were upregulated in juvenile cuttings. Concomitantly, a transient burst of NO was observed upon excision, which was higher in juvenile cuttings than in mature ones. Treatment with an NO donor improved rooting of both juvenile and mature cuttings. A single NIA gene was found in the newly released E. grandis genome sequence, the cDNA of which was isolated, overexpressed in Arabidopsis plants and shown to increase NO production in intact plants. Therefore, higher levels of NIA in E. grandis juvenile cuttings might lead to increased ability to produce NO and to form adventitious roots. Arabidopsis transgenic plants constantly expressing EgNIA did not exhibit a significantly higher lateral or adventitious root formation, suggesting that spatial and temporal rather than a constitutive increase in NO is favorable for root differentiation.