Nitrate sensing by the maize root apex transition zone: a merged transcriptomic and proteomic survey

A system for the study of roots 3D kinematics in hydroponic culture: a study on the oscillatory features of root tip

BACKGROUND

The root of a plant is a fundamental organ for the multisensory perception of the environment. Investigating root growth dynamics as a mean of their interaction with the environment is of key importance for improving knowledge in plant behaviour, plant biology and agriculture. To date, it is difficult to study roots movements from a dynamic perspective given that available technologies for root imaging focus mostly on static characterizations, lacking temporal and three-dimensional (3D) spatial information. This paper describes a new system based on time-lapse for the 3D reconstruction and analysis of roots growing in hydroponics.

RESULTS

The system is based on infrared stereo-cameras acquiring time-lapse images of the roots for 3D reconstruction. The acquisition protocol guarantees the root growth in complete dark while the upper part of the plant grows in normal light conditions. The system extracts the 3D trajectory of the root tip and a set of descriptive features in both the temporal and frequency domains. The system has been used on Zea mays L. (B73) during the first week of growth and shows good inter-reliability between operators with an Intra Class Correlation Coefficient (ICC) > 0.9 for all features extracted. It also showed measurement accuracy with a median difference of < 1 mm between computed and manually measured root length.

CONCLUSIONS

The system and the protocol presented in this study enable accurate 3D analysis of primary root growth in hydroponics. It can serve as a valuable tool for analysing real-time root responses to environmental stimuli thus improving knowledge on the processes contributing to roots physiological and phenotypic plasticity.

Molecular hydrogen positively regulates nitrate uptake and seed size by targeting nitrate reductase

Although the sources of molecular hydrogen (H2) synthesis in plants remain to be fully elucidated, ample evidence shows that plant-based H2 can regulate development and stress responses. Here, we present genetic and molecular evidence indicating that nitrate reductase (NR) might be a target of H2 sensing that positively regulates nitrogen use efficiency (NUE) and seed size in Arabidopsis (Arabidopsis thaliana). The expression level of NR and changes of NUE under control and, in particular, low nitrogen supply were positively associated with H2 addition supplied exogenously or through genetic manipulation. The improvement in nitrate assimilation achieved by H2 was also mediated via NR dephosphorylation. H2 control of seed size was impaired by NR mutation. Further genetic evidence revealed that H2, NR, and nitric oxide can synergistically regulate nitrate assimilation in response to N starvation conditions. Collectively, our data indicate that NR might be a target for H2 sensing, ultimately positively regulating nitrate uptake and seed size. These results provide insights into H2 signaling and its functions in plant metabolism.

Proteomic analysis of leaves and roots during drought stress and recovery in Setaria italica L

Drought is a major environmental factor that limits agricultural crop productivity and threatens food security. Foxtail millet is a model crop with excellent abiotic stress tolerance and is consequently an important subject for obtaining a better understanding of the molecular mechanisms underlying plant responses to drought and recovery. Here the physiological and proteomic responses of foxtail millet (cultivar Yugu1) leaves and roots to drought treatments and recovery were evaluated. Drought-treated foxtail millet exhibited increased relative electrolyte leakage and decreased relative water content and chlorophyll content compared to control and rewatering plants. A global analysis of protein profiles was evaluated for drought-treated and recovery treatment leaves and roots. We also identified differentially abundant proteins in drought and recovery groups, enabling comparisons between leaf and root tissue responses to the conditions. The principal component analysis suggested a clear distinction between leaf and root proteomes for the drought-treated and recovery treatment plants. Gene Ontology enrichment and co-expression analyses indicated that the biological responses of leaves differed from those in roots after drought and drought recovery. These results provide new insights and data resources to investigate the molecular basis of tissue-specific functional responses of foxtail millet during drought and recovery, thereby significantly informing crop breeding.

The Nitrate Transporter MtNPF6.8 Is a Master Sensor of Nitrate Signal in the Primary Root Tip of Medicago truncatula

Nitrate is not only an essential nutrient for plants, but also a signal involved in plant development. We have previously shown in the model legume Medicago truncatula, that the nitrate signal, which restricts primary root growth, is mediated by MtNPF6.8, a nitrate transporter. Nitrate signal also induces changes in reactive oxygen species accumulation in the root tip due to changes in cell wall peroxidase (PODs) activity. Thus, it was interesting to determine the importance of the role of MtNPF6.8 in the regulation of the root growth by nitrate and identify the POD isoforms responsible for the changes in POD activity. For this purpose, we compared in M. truncatula a npf6.8 mutant and nitrate insensitive line deficient in MtNPF6.8 and the corresponding wild and sensitive genotype for their transcriptomic and proteomic responses to nitrate. Interestingly, only 13 transcripts and no protein were differently accumulated in the primary root tip of the npf6.8-3 mutant line in response to nitrate. The sensitivity of the primary root tip to nitrate appeared therefore to be strongly linked to the integrity of MtNPF6.8 which acts as a master mediator of the nitrate signal involved in the control of the root system architecture. In parallel, 7,259 and 493 genes responded, respectively, at the level of transcripts or proteins in the wild type, 196 genes being identified by both their transcript and protein. By focusing on these 196 genes, a concordance of expression was observed for most of them with 143 genes being up-regulated and 51 being down-regulated at the two gene expression levels. Their ontology analysis uncovered a high enrichment in POD genes, allowing the identification of POD candidates involved in the changes in POD activity previously observed in response to nitrate.

Strigolactones and Auxin Cooperate to Regulate Maize Root Development and Response to Nitrate

In maize, nitrate regulates root development thanks to the coordinated action of many players. In this study, the involvement of strigolactones (SLs) and auxin as putative components of the nitrate regulation of lateral root (LR) was investigated. To this aim, the endogenous SL content of maize root in response to nitrate was assessed by liquid chromatography with tandem mass Spectrometry (LC-MS/MS) and measurements of LR density in the presence of analogues or inhibitors of auxin and SLs were performed. Furthermore, an untargeted RNA-sequencing (RNA-seq)-based approach was used to better characterize the participation of auxin and SLs to the transcriptional signature of maize root response to nitrate. Our results suggested that N deprivation induces zealactone and carlactonoic acid biosynthesis in root, to a higher extent if compared to P-deprived roots. Moreover, data on LR density led to hypothesize that the induction of LR development early occurring upon nitrate supply involves the inhibition of SL biosynthesis, but that the downstream target of SL shutdown, besides auxin, also includes additional unknown players. Furthermore, RNA-seq results provided a set of putative markers for the auxin- or SL-dependent action of nitrate, meanwhile also allowing to identify novel components of the molecular regulation of maize root response to nitrate. Globally, the existence of at least four different pathways was hypothesized: one dependent on auxin, a second one mediated by SLs, a third deriving from the SL-auxin interplay, and a last one attributable to nitrate itself through further downstream signals. Further work will be necessary to better assess the reliability of the model proposed.

Nitrate Regulates Maize Root Transcriptome through Nitric Oxide Dependent and Independent Mechanisms

Maize root responds to nitrate by modulating its development through the coordinated action of many interacting players. Nitric oxide is produced in primary root early after the nitrate provision, thus inducing root elongation. In this study, RNA sequencing was applied to discover the main molecular signatures distinguishing the response of maize root to nitrate according to their dependency on, or independency of, nitric oxide, thus discriminating the signaling pathways regulated by nitrate through nitric oxide from those regulated by nitrate itself of by further downstream factors. A set of subsequent detailed functional annotation tools (Gene Ontology enrichment, MapMan, KEGG reconstruction pathway, transcription factors detection) were used to gain further information and the lateral root density was measured both in the presence of nitrate and in the presence of nitrate plus cPTIO, a specific NO scavenger, and compared to that observed for N-depleted roots. Our results led us to identify six clusters of transcripts according to their responsiveness to nitric oxide and to their regulation by nitrate provision. In general, shared and specific features for the six clusters were identified, allowing us to determine the overall root response to nitrate according to its dependency on nitric oxide.

Gibberellin Signaling Promotes the Secondary Growth of Storage Roots in Panax ginseng

Gibberellins (GAs) are an important group of phytohormones associated with diverse growth and developmental processes, including cell elongation, seed germination, and secondary growth. Recent genomic and genetic analyses have advanced our knowledge of GA signaling pathways and related genes in model plant species. However, functional genomics analyses of GA signaling pathways in Panax ginseng, a perennial herb, have rarely been carried out, despite its well-known economical and medicinal importance. Here, we conducted functional characterization of GA receptors and investigated their physiological roles in the secondary growth of P. ginseng storage roots. We found that the physiological and genetic functions of P. ginseng gibberellin-insensitive dwarf1s (PgGID1s) have been evolutionarily conserved. Additionally, the essential domains and residues in the primary protein structure for interaction with active GAs and DELLA proteins are well-conserved. Overexpression of PgGID1s in Arabidopsis completely restored the GA deficient phenotype of the Arabidopsis gid1a gid1c (atgid1a/c) double mutant. Exogenous GA treatment greatly enhanced the secondary growth of tap roots; however, paclobutrazol (PCZ), a GA biosynthetic inhibitor, reduced root growth in P. ginseng. Transcriptome profiling of P. ginseng roots revealed that GA-induced root secondary growth is closely associated with cell wall biogenesis, the cell cycle, the jasmonic acid (JA) response, and nitrate assimilation, suggesting that a transcriptional network regulate root secondary growth in P. ginseng. These results provide novel insights into the mechanism controlling secondary root growth in P. ginseng.

Nitrogen Uptake in Plants: The Plasma Membrane Root Transport Systems from a Physiological and Proteomic Perspective

Nitrogen nutrition in plants is a key determinant in crop productivity. The availability of nitrogen nutrients in the soil, both inorganic (nitrate and ammonium) and organic (urea and free amino acids), highly differs and influences plant physiology, growth, metabolism, and root morphology. Deciphering this multifaceted scenario is mandatory to improve the agricultural sustainability. In root cells, specific proteins located at the plasma membrane play key roles in the transport and sensing of nitrogen forms. This review outlines the current knowledge regarding the biochemical and physiological aspects behind the uptake of the individual nitrogen forms, their reciprocal interactions, the influences on root system architecture, and the relations with other proteins sustaining fundamental plasma membrane functionalities, such as aquaporins and H⁺-ATPase. This topic is explored starting from the information achieved in the model plant Arabidopsis and moving to crops in agricultural soils. Moreover, the main contributions provided by proteomics are described in order to highlight the goals and pitfalls of this approach and to get new hints for future studies.

The attachment process and physiological properties of Escherichia coli O157:H7 on quartz

Background

Manure application and sewage irrigation release many intestinal pathogens into the soil. After being introduced into the soil matrix, pathogens are commonly found to attach to soil minerals. Although the survival of mineral-associated Escherichia coli O157:H7 has been studied, a comprehensive understanding of the attachment process and physiological properties after attachment is still lacking.

Results

In this study, planktonic and attached Escherichia coli O157:H7 cells on quartz were investigated using RNA sequencing (RNA-seq) and the isobaric tagging for relative and absolute quantitation (iTRAQ) proteomic method. Based on the transcriptomic and proteomic analyses and gene knockouts, functional two-component system pathways were required for efficient attachment; chemotaxis and the Rcs system were identified to play determinant roles in E. coli O157:H7 attachment on quartz. After attachment, the pyruvate catabolic pathway shifted from the tricarboxylic acid (TCA) cycle toward the fermentative route. The survival rate of attached E. coli O157:H7 increased more than 10-fold under penicillin and vancomycin stress and doubled under alkaline pH and ferric iron stress.

Conclusions

These results contribute to the understanding of the roles of chemotaxis and the Rcs system in the attachment process of pathogens and indicate that the attachment of pathogens to minerals significantly elevates their resistance to antibiotics and environmental stress, which may pose a potential threat to public health.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-020-02043-8.

Up-regulating GmETO1 improves phosphorus uptake and use efficiency by promoting root growth in soybean

Soybean is a high inorganic phosphate (Pi) demanding crop; its production is strongly suppressed when Pi is deficient in soil. However, the regulatory mechanism of Pi deficiency tolerance in soybean is still largely unclear. Here, our findings highlighted the pivotal role of the ethylene-associated pathway in soybean tolerance to Pi deficiency by comparatively studying transcriptome changes between a representative Pi-deficiency-tolerant soybean genotype NN94156 and a sensitive genotype Bogao under different Pi supplies. By further integrating high-confident linkage and association mapping, we identified that Ethylene-Overproduction Protein 1 (GmETO1), an essential ethylene-biosynthesis regulator, underlies the major quantitative trait locus (QTL) q14-2 controlling Pi uptake. GmETO1 was also the representative member of ETO1 family members that was strongly induced by Pi deficiency. Overexpressing GmETO1 significantly enhanced Pi deficiency tolerance by increasing proliferation and elongation of hairy roots, Pi uptake and use efficiency, and conversely, silencing of GmETO1 led to opposite findings. We further demonstrated that Pi-deficiency inducible genes critical for root morphological and physiological traits including GmACP1/2, Pht1;4, Expansin-A7 and Root Primordium Defective 1 functioned downstream of GmETO1. Our study provides comprehensive insight into the complex regulatory mechanism of Pi deficiency tolerance in soybean and a potential way to genetically improve soybean low-Pi tolerance.

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.

Cross-Species Root Transcriptional Network Analysis Highlights Conserved Modules in Response to Nitrate between Maize and Sorghum

Plants have evolved complex mechanisms to respond to the fluctuation of available nitrogen (N) in soil, but the genetic mechanisms underlying the N response in crops are not well-documented. In this study, we generated a time series of NO₃⁻-mediated transcriptional profiles in roots of maize and sorghum, respectively. Using weighted gene co-expression network analysis, we identified modules of co-expressed genes that related to NO₃⁻ treatments. A cross-species comparison revealed 22 conserved modules, of which four were related to hormone signaling, suggesting that hormones participate in the early nitrate response. Three other modules are composed of genes that are mainly upregulated by NO₃⁻ and involved in nitrogen and carbohydrate metabolism, including NRT, NIR, NIA, FNR, and G6PD2. Two G2-like transcription factors (ZmNIGT1 and SbNIGT1), induced by NO₃⁻ stimulation, were identified as hub transcription factors (TFs) in the modules. Transient assays demonstrated that ZmNIGT1 and SbNIGT1 are transcriptional repressors. We identified the target genes of ZmNIGT1 by DNA affinity-purification sequencing (DAP-Seq) and found that they were significantly enriched in catalytic activity, including carbon, nitrogen, and other nutrient metabolism. A set of ZmNIGT1 targets encode transcription factors (ERF, ARF, and AGL) that are involved in hormone signaling and root development. We propose that ZmNIGT1 and SbNIGT1 are negative regulators of nitrate responses that play an important role in optimizing nutrition metabolism and root morphogenesis. Together with conserved N responsive modules, our study indicated that, to encounter N variation in soil, maize and sorghum have evolved an NO₃⁻-regulatory network containing a set of conserved modules and transcription factors.

Nitrate and Ammonium Affect the Overall Maize Response to Nitrogen Availability by Triggering Specific and Common Transcriptional Signatures in Roots

Nitrogen (N) is an essential macronutrient for crops. Plants have developed several responses to N fluctuations, thus optimizing the root architecture in response to N availability. Nitrate and ammonium are the main inorganic N forms taken up by plants, and act as both nutrients and signals, affecting gene expression and plant development. In this study, RNA-sequencing was applied to gain comprehensive information on the pathways underlying the response of maize root, pre-treated in an N-deprived solution, to the provision of nitrate or ammonium. The analysis of the transcriptome shows that nitrate and ammonium regulate overlapping and distinct pathways, thus leading to different responses. Ammonium activates the response to stress, while nitrate acts as a negative regulator of transmembrane transport. Both the N-source repress genes related to the cytoskeleton and reactive oxygen species detoxification. Moreover, the presence of ammonium induces the accumulation of anthocyanins, while also reducing biomass and chlorophyll and flavonoids accumulation. Furthermore, the later physiological effects of these nutrients were evaluated through the assessment of shoot and root growth, leaf pigment content and the amino acid concentrations in root and shoot, confirming the existence of common and distinct features in response to the two nitrogen forms.

Root Handling Affects Carboxylates Exudation and Phosphate Uptake of White Lupin Roots

The reliable quantification of root exudation and nutrient uptake is a very challenging task, especially when considering single root segments. Most methods used necessitate root handling e.g. root dissecting/cutting. However, there is a knowledge gap on how much these techniques affect root physiology. Thus, this study aimed at assessing the effect of different root handling techniques on the phosphate (P_i) uptake and carboxylate exudation of white lupin roots. White lupin plants were grown hydroponically in a full and P_i-deficient nutrient solution for 60 days. Phosphate uptake and carboxylate exudation of cluster and non-cluster roots were measured using custom made cells 1, 4, and 8 h after the onset of light. Three different experimental set-ups were used: i) without cutting the root apparatus from the shoots, nor dissecting the root into smaller root sections - named intact plant (IP); ii) separating the roots from the shoots, without dissecting the root into smaller sections - named intact root (IR); iii) separating the roots form the shoots and dissecting the roots in different sections-named dissected roots (DR). The sampling at 8 h led to the most significant alterations of the root P_i uptake induced by the sampling method. Generally, roots were mainly affected by the DR sampling method, indicating that results of studies in which roots are cut/dissected should be interpreted carefully. Additionally, the study revealed that the root tip showed a very high P_i uptake rate, suggesting that the tip could act as a P_i sensor. Citrate, malate and lactate could be detected in juvenile, mature and senescent cluster root exudation. We observed a significant effect of the handling method on carboxylate exudation only at sampling hours 1 and 8, although no clear and distinctive trend could be observed. Results here presented reveal that the root handling as well as the sampling time point can greatly influence root physiology and therefore should not be neglected when interpreting rhizosphere dynamics.

An Integrated Analysis of the Rice Transcriptome and Metabolome Reveals Root Growth Regulation Mechanisms in Response to Nitrogen Availability

Nitrogen is an essential nutrient for plant growth and basic metabolic processes. Root systems play an important role in the ability of plants to obtain nutrients from the soil, and are closely related to the growth and development of above-ground plants. Root morphology analysis showed that root growth was induced under low-nitrogen conditions and inhibited under high-nitrogen conditions. To better understand the molecular mechanisms and metabolic basis underlying the rice root response to nitrogen availability, an integrated analysis of the rice root transcriptome and metabolome under three environmental conditions (low-, control, and high-nitrogen conditions) was conducted. A total of 262 and 262 differentially level metabolites were identified under low- and high-nitrogen conditions, respectively. A total of 696 and 808 differentially expressed genes were identified under low- and high-nitrogen conditions, respectively. For both the differentially expressed genes and metabolites, KEGG pathway analysis indicated that amino acid metabolism, carbon and nitrogen metabolism, phenylpropanoid metabolism, and phytohormones’ signal transduction were significantly affected by nitrogen availability. Additionally, variable levels of 65 transcription factors (TFs) were identified in rice leaves exposed to high and low nitrogen, covering 22 TF families. These results also indicate that there is a significant difference in the transcriptional regulation mechanisms of rice roots between low and high nitrogen. In summary, our study provides new information for a further understanding of the response of rice roots to low-nitrogen and high-nitrogen conditions.

Combined transcriptomics and proteomics forecast analysis for potential genes regulating the Columbian plumage color in chickens

BACKGROUND

Coloration is one of the most recognizable characteristics in chickens, and clarifying the coloration mechanisms will help us understand feather color formation. "Yufen I" is a commercial egg-laying chicken breed in China that was developed by a three-line cross using lines H, N and D. Columbian plumage is a typical feather character of the "Yufen I" H line. To elucidate the molecular mechanism underlying the pigmentation of Columbian plumage, this study utilizes high-throughput sequencing technology to compare the transcriptome and proteome differences in the follicular tissue of different feathers, including the dorsal neck with black and white striped feather follicles (Group A) and the ventral neck with white feather follicles (Group B) in the "Yufen I" H line.

RESULTS

In this study, we identified a total of 21,306 genes and 5,203 proteins in chicken feather follicles. Among these, 209 genes and 382 proteins were differentially expressed in two locations, Group A and Group B, respectively. A total of 8 differentially expressed genes (DEGs) and 9 differentially expressed proteins (DEPs) were found to be involved in the melanogenesis pathway. Additionally, a specifically expressed MED23 gene and a differentially expressed GNAQ protein were involved in melanin synthesis. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis mapped 190 DEGs and 322 DEPs to 175 and 242 pathways, respectively, and there were 166 pathways correlated with both DEGs and DEPs. 49 DEPs/DEGs overlapped and were enriched for 12 pathways. Transcriptomic and proteomic analyses revealed that the following pathways were activated: melanogenesis, cardiomyocyte adrenergic, calcium and cGMP-PKG. The expression of DEGs was validated by real-time quantitative polymerase chain reaction (qRT-PCR) that produced results similar to those from RNA-seq. In addition, we found that the expression of the MED23, FZD10, WNT7B and WNT11 genes peaked at approximately 8 weeks in the "Yufen I" H line, which is consistent with the molting cycle. As both groups showed significant differences in terms of the expression of the studied genes, this work opens up avenues for research in the future to assess their exact function in determining plumage color.

CONCLUSION

Common DEGs and DEPs were enriched in the melanogenesis pathway. MED23 and GNAQ were also reported to play a crucial role in melanin synthesis. In addition, this study is the first to reveal gene and protein variations in in the "Yufen I" H line during Columbian feather color development and to discover principal genes and proteins that will aid in functional genomics studies in the future. The results of the present study provide a significant conceptual basis for the future breeding schemes with the "Yufen I" H line and provide a basis for research on the mechanisms of feather pigmentation.

The Control of Zealactone Biosynthesis and Exudation is Involved in the Response to Nitrogen in Maize Root

Nitrate acts as a signal in regulating plant development in response to environment. In particular nitric oxide, auxin and strigolactones (SLs) were supposed to cooperate to regulate the maize root response to this anion. In this study, a combined approach based on liquid chromatography-quadrupole/time-of-flight tandem mass spectrometry and on physiological and molecular analyses was adopted to specify the involvement of SLs in the maize response to N. Our results showed that N deficiency strongly induces SL exudation, likely through stimulating their biosynthesis. Nitrate provision early counteracts and also ammonium lowers SL exudation, but less markedly. Exudates obtained from N-starved and ammonium-provided seedlings stimulated Phelipanche germination, whereas when seeds were treated with exudates harvested from nitrate-provided plants no germination was observed. Furthermore, our findings support the idea that the inhibition of SL production observed in response to nitrate and ammonium would contribute to the regulation of lateral root development. Moreover, the transcriptional regulation of a gene encoding a putative maize WBC transporter, in response to various nitrogen supplies, together with its mRNA tissue localization, supported its role in SL allocation. Our results highlight the dual role of SLs as molecules able to signal outwards a nutritional need and as endogenous regulators of root architecture adjustments to N, thus synchronizing plant growth with nitrogen acquisition.

Nitric oxide and plant mineral nutrition: current knowledge

Plants under conditions of essential mineral deficiency trigger signaling mechanisms that involve common components. Among these components, nitric oxide (NO) has been identified as a key participant in responses to changes in nutrient availability. Usually, nutrient imbalances affect the levels of NO in specific plant tissues, via modification of its rate of synthesis or degradation. Changes in the level of NO affect plant morphology and/or trigger responses associated with nutrient homeostasis, mediated by its interaction with reactive oxygen species, phytohormones, and through post-translational modification of proteins. NO-related events constitute an exciting field of research to understand how plants adapt and respond to conditions of nutrient shortage. This review summarizes the current knowledge on NO as a component of the multiple processes related to plant performance under conditions of deficiency in mineral nutrients, focusing on macronutrients such as nitrogen, phosphate, potassium, and magnesium, as well as micronutrients such as iron and zinc.

Nitrate affects transcriptional regulation of UPBEAT1 and ROS localisation in roots of Zea mays L

Nitrogen (N) is an indispensable nutrient for crops but its availability in agricultural soils is subject to considerable fluctuation. Plants have developed plastic responses to external N fluctuations in order to optimise their development. The coordinated action of nitric oxide and auxin seems to allow the cells of the root apex transition zone (TZ) of N-deprived maize to rapidly sense nitrate (NO₃ ^- ). Preliminary results support the hypothesis that reactive oxygen species (ROS) signalling might also have a role in this pathway, probably through a putative maize orthologue of UPBEAT1 (UPB1). To expand on this hypothesis and better understand the different roles played by different root portions, we investigated the dynamics of ROS production, and the molecular and biochemical regulation of the main components of ROS production and scavenging in tissues of the meristem, transition zone, elongation zone and maturation zone of maize roots. The results suggest that the inverse regulation of ZmUPB1 and ZmPRX112 transcription observed in cells of the TZ in response to nitrogen depletion or NO₃ ^- supply affects the balance between superoxide (O₂ ^•- ) and hydrogen peroxide (H₂ O₂ ) in the root apex and consequently triggers differential root growth. This explanation is supported by additional results on the overall metabolic and transcriptional regulation of ROS homeostasis.

Adaption of Roots to Nitrogen Deficiency Revealed by 3D Quantification and Proteomic Analysis

Rapeseed (Brassica napus) is an important oil crop worldwide. However, severe inhibition of rapeseed production often occurs in the field due to nitrogen (N) deficiency. The root system is the main organ to acquire N for plant growth, but little is known about the mechanisms underlying rapeseed root adaptions to N deficiency. Here, dynamic changes in root architectural traits of N-deficient rapeseed plants were evaluated by 3D in situ quantification. Root proteome responses to N deficiency were analyzed by the tandem mass tag-based proteomics method, and related proteins were characterized further. Under N deficiency, rapeseed roots become longer, with denser cells in the meristematic zone and larger cells in the elongation zone of root tips, and also become softer with reduced solidity. A total of 171 and 755 differentially expressed proteins were identified in short- and long-term N-deficient roots, respectively. The abundance of proteins involved in cell wall organization or biogenesis was highly enhanced, but most identified peroxidases were reduced in the N-deficient roots. Notably, peroxidase activities also were decreased, which might promote root elongation while lowering the solidity of N-deficient roots. These results were consistent with the cell wall components measured in the N-deficient roots. Further functional analysis using transgenic Arabidopsis (Arabidopsis thaliana) plants demonstrated that the two root-related differentially expressed proteins contribute to the enhanced root growth under N deficiency conditions. These results provide insights into the global changes of rapeseed root responses to N deficiency and may facilitate the development of rapeseed cultivars with high N use efficiency through root-based genetic improvements.

Potential Root Foraging Strategy of Wheat (Triticum aestivum L.) for Potassium Heterogeneity

Potassium (K) distribution is horizontally heterogeneous under the conservation agriculture approach of no-till with strip fertilization. The root foraging strategy of wheat for K heterogeneity is poorly understood. In this study, WinRHIZO, microarray, Non-invasive Micro-test Technology (NMT) and a split-root system were performed to investigate root morphology, gene expression profiling and fluxes of K+ and O2 under K heterogeneity and homogeneity conditions. The split-root system was performed as follows: C. LK (both compartments had low K), C. NK (both compartments had normal K), Sp. LK (one compartment had low K) and Sp. NK (the other compartment had normal K). The ratio of total root length and root tips in Sp. NK was significantly higher than that in C. NK, while no significant differences were found between Sp. LK and C. LK. Differential expression genes in C. LK vs. C. NK had opposite responses in Sp. LK vs. C. LK and similar responses in Sp. NK vs. C. NK. Low-K responsive genes, such as peroxidases, mitochondrion, transcription factor activity, calcium ion binding, glutathione transferase and cellular respiration genes were found to be up-regulated in Sp. NK. However, methyltransferase activity, protein amino acid phosphorylation, potassium ion transport, and protein kinase activity genes were found to be down-regulated in Sp. LK. The up-regulated gene with function in respiration tended to increase K+ uptake through improving O2 influx on the root surface in Sp. NK, while the down-regulated genes with functions of K+ and O2 transport tended to reduce K+ uptake on the root surface in Sp. LK. To summarize, wheat roots tended to perform active-foraging strategies in Sp. NK and dormant-foraging strategies in Sp. LK through the following patterns: (1) root development in Sp. NK but not in Sp. LK; (2) low-K responsive genes, such as peroxidases, mitochondrion, transcription factor activity, calcium ion binding and respiration, were up-regulated in Sp. NK but not in Sp. LK; and (3) root K+ and O2 influxes increased in Sp. NK but not in Sp. LK. Our findings may better explain the optimal root foraging strategy for wheat grown with heterogeneous K distribution in the root zone.

Formation of a subero-lignified apical deposit in root tip of radish (Raphanus sativus) as a response to copper stress

BACKGROUND AND AIMS

Heavy metals induce changes in root metabolism and physiology, which can lead to a complex remodelling of the root system. The final morphological responses of radish (Raphanus sativus) roots exposed to toxic concentrations of the heavy metal (Cu) include root growth inhibition, differentiation of xylem vessels close to the root tip, enhanced suberin lamellae deposition and enhanced lateral root production. Recently, we have found that such changes in root morphology and anatomy are coupled to the formation of a subero-lignified apical deposit (SLAD) very close to the root tip.

METHODS

To clarify the details of the formation of a SLAD in the root tip, we conducted experiments with radish roots exposed to a high Cu concentration (60 µm). Histochemical analysis of lignin and suberin as well as analysis of spatial-temporal characteristics of SLAD formation were performed by bright-field, fluorescence and confocal microscopy.

KEY RESULTS

This unique structure, not longer than 100 µm, consists of modified cell walls of the central cylinder that are encircled by a short cylinder of prematurely suberized endodermal cells. A SLAD starts to form, in both primary and lateral roots, after cessation of root elongation, and it is coupled with xylem differentiation and root branching close to the root apex. We noticed that deposition of phenolic substances into a SLAD, mainly suberin in the endodermis, is spatially separated from suberization or lignification in basally located endodermis.

CONCLUSIONS

Although the main reason for formation of a SLAD is elusive, we suggest that it is a part of stress-induced responses which relate to decreased root growth or permeability in heavy metal stress.

Integrated genomics, physiology and breeding approaches for improving nitrogen use efficiency in potato: translating knowledge from other crops

Potato plays a key role in global food and nutritional security. Potato is an N fertiliser-responsive crop, producing high tuber yields. However, excessive use of N can result in environmental damage and high production costs, hence improving nitrogen use efficiency (NUE) of potato plants is one of the sustainable options to address these issues and increase yield. Advanced efforts have been undertaken to improve NUE in other plants like Arabidopsis, rice, wheat and maize through molecular and physiological approaches. Conversely, in potato, NUE studies have predominantly focussed on agronomy or soil management, except for a few researchers who have measured gene expression and proteins relevant to N uptake or metabolism. The focus of this review is to adapt knowledge gained from other plants to inform investigation of N metabolism and associated traits in potato with the aim of improving potato NUE using integrated genomics, physiology and breeding methods.

Genome-wide proteomic profiling reveals the role of dominance protein expression in heterosis in immature maize ears

Heterosis refers to the phenomenon in which hybrid progeny show superior performance relative to their parents. Early maize ear development shows strong heterosis in ear architecture traits and greatly affects grain yield. To explore the underlying molecular mechanisms, genome-wide proteomics of immature ears of maize hybrid ZD909 and its parents were analyzed using tandem mass tag (TMT) technology. A total of 9,713 proteins were identified in all three genotypes. Among them, 3,752 (38.6%) proteins were differentially expressed between ZD909 and its parents. Multiple modes of protein action were discovered in the hybrid, while dominance expression patterns accounted for 63.6% of the total differentially expressed proteins (DEPs). Protein pathway enrichment analysis revealed that high parent dominance proteins mainly participated in carbon metabolism and nitrogen assimilation processes. Our results suggested that the dominant expression of favorable alleles related to C/N metabolism in the hybrid may be essential for ZD909 ear growth and heterosis formation. Integrated analysis of proteomic and quantitative trait locus (QTL) data further support our DEP identification and provide useful information for the discovery of genes associated with ear development. Our study provides comprehensive insight into the molecular mechanisms underlying heterosis in immature maize ears from a proteomic perspective.

Comparative Proteomic Analysis of Paulownia fortunei Response to Phytoplasma Infection with Dimethyl Sulfate Treatment

Paulownia fortunei is a widely cultivated economic forest tree species that is susceptible to infection with phytoplasma, resulting in Paulownia witches' broom (PaWB) disease. Diseased P. fortunei is characterized by stunted growth, witches' broom, shortened internodes, and etiolated and smaller leaves. To understand the molecular mechanism of its pathogenesis, we applied isobaric tags for relative and absolute quantitation (iTRAQ) and liquid chromatography coupled with tandem mass spectrometry approaches to study changes in the proteomes of healthy P. fortunei, PaWB-infected P. fortunei, and PaWB-infected P. fortunei treated with 15 mg·L⁻¹ or 75 mg·L⁻¹ dimethyl sulfate. We identified 2969 proteins and 104 and 32 differentially abundant proteins that were phytoplasma infection responsive and dimethyl sulfate responsive, respectively. Based on our analysis of the different proteomes, 27 PaWB-related proteins were identified. The protein-protein interactions of these 27 proteins were analyzed and classified into four groups (photosynthesis-related, energy-related, ribosome-related, and individual proteins). These PaWB-related proteins may help in developing a deeper understanding of how PaWB affects the morphological characteristics of P. fortunei and further establish the mechanisms involved in the response of P. fortunei to phytoplasma.

Differential proteomic analysis of replanted Rehmannia glutinosa roots by iTRAQ reveals molecular mechanisms for formation of replant disease

BACKGROUND

The normal growth of Rehmannia glutinosa, a widely used medicinal plant in China, is severely disturbed by replant disease. The formation of replant disease commonly involves interactions among plants, allelochemicals and microbes; however, these relationships remain largely unclear. As a result, no effective measures are currently available to treat replant disease.

RESULTS

In this study, an integrated R. glutinosa transcriptome was constructed, from which an R. glutinosa protein library was obtained. iTRAQ technology was then used to investigate changes in the proteins in replanted R. glutinosa roots, and the proteins that were expressed in response to replant disease were identified. An integrated R. glutinosa transcriptome from different developmental stages of replanted and normal-growth R. glutinosa produced 65,659 transcripts, which were accurately translated into 47,818 proteins. Using this resource, a set of 189 proteins was found to be significantly differentially expressed between normal-growth and replanted R. glutinosa. Of the proteins that were significantly upregulated in replanted R. glutinosa, most were related to metabolism, immune responses, ROS generation, programmed cell death, ER stress, and lignin synthesis.

CONCLUSIONS

By integrating these key events and the results of previous studies on replant disease formation, a new picture of the damaging mechanisms that cause replant disease stress emerged. Replant disease altered the metabolic balance of R. glutinosa, activated immune defence systems, increased levels of ROS and antioxidant enzymes, and initiated the processes of cell death and senescence in replanted R. glutinosa. Additionally, lignin deposition in R. glutinosa roots that was caused by replanting significantly inhibited tuberous root formation. These key processes provide important insights into the underlying mechanisms leading to the formation of replant disease and also for the subsequent development of new control measures to improve production and quality of replanted plants.

Comparative Proteomic Analysis of Flag Leaves Reveals New Insight into Wheat Heat Adaptation

Hexaploid wheat (Triticum aestivum L.) is an important food crop but it is vulnerable to heat. The heat-responsive proteome of wheat remains to be fully elucidated because of previous technical and genomic limitations, and this has hindered our understanding of the mechanisms of wheat heat adaptation and advances in improving thermotolerance. Here, flag leaves of wheat during grain filling stage were subjected to high daytime temperature stress, and 258 heat-responsive proteins (HRPs) were identified with iTRAQ analysis. Enrichment analysis revealed that chlorophyll synthesis, carbon fixation, protein turnover, and redox regulation were the most remarkable heat-responsive processes. The HRPs involved in chlorophyll synthesis and carbon fixation were significantly decreased, together with severe membrane damage, demonstrating the specific effects of heat on photosynthesis of wheat leaves. In addition, the decrease in chlorophyll content may result from the decrease in HRPs involved in chlorophyll precursor synthesis. Further analysis showed that the accumulated effect of heat stress played a critical role in photosynthesis reduction, suggested that improvement in heat tolerance of photosynthesis, and extending heat tolerant period would be major research targets. The significantly accumulation of GSTs and Trxs in response to heat suggested their important roles in redox regulation, and they could be the promising candidates for improving wheat thermotolerance. In summary, our results provide new insight into wheat heat adaption and provide new perspectives on thermotolerance improvement.

Spatiotemporal variation of nitrate uptake kinetics within the maize (Zea mays L.) root system is associated with greater nitrate uptake and interactions with architectural phenes

Increasing maize nitrogen acquisition efficiency is a major goal for the 21st century. Nitrate uptake kinetics (NUK) are defined by I max and K m, which denote the maximum uptake rate and the affinity of transporters, respectively. Because NUK have been studied predominantly at the molecular and whole-root system levels, little is known about the functional importance of NUK variation within root systems. A novel method was created to measure NUK of root segments that demonstrated variation in NUK among root classes (seminal, lateral, crown, and brace). I max varied among root class, plant age, and nitrate deprivation combinations, but was most affected by plant age, which increased I max, and nitrate deprivation time, which decreased I max K m was greatest for crown roots. The functional-structural simulation SimRoot was used for sensitivity analysis of plant growth to root segment I max and K m, as well as to test interactions of I max with root system architectural phenes. Simulated plant growth was more sensitive to I max than K m, and reached an asymptote near the maximum I max observed in the empirical studies. Increasing the I max of lateral roots had the largest effect on shoot growth. Additive effects of I max and architectural phenes on nitrate uptake were observed. Empirically, only lateral root tips aged 20 d operated at the maximum I max, and simulations demonstrated that increasing all seminal and lateral classes to this maximum rate could increase plant growth by as much as 26%. Therefore, optimizing I max for all maize root classes merits attention as a promising breeding goal.

NAR2.1/NRT2.1 functional interaction with NO3(-) and H(+) fluxes in high-affinity nitrate transport in maize root regions

Spatial and temporal fluctuations in nitrate (NO3(-)) availability are very common in agricultural soils. Therefore, understanding the molecular and physiological mechanisms involved in regulating NO3(-) uptake in regions along the primary root is important for improving the NO3(-) uptake efficiency (NUpE) in crops. Different regions of maize primary root, named R1, R2 and R3, NO3(-) starved for 3 days, were exposed to 50 μM NO3(-). Electrophysiological measurements (membrane potential and H(+) and NO3(-) fluxes) and NPF6.3, NRT2.1, NAR2.1, MHA1, MHA3 and MHA4 gene expression analyses were carried out. The results confirmed variable spatial and temporal patterns in both NO3(-) and H(+) fluxes and gene expression along the primary maize root. A significant correlation (P = 0.0023) between nitrate influx and gene transcript levels was observed only when NAR2.1 and NRT2.1 co-expression were considered together, showing for the first time the NRT2.1/NAR2.1 functional interaction in nitrate uptake along the root axis. Taken together these results suggest differing roles among the primary root regions, in which the apical part seem to be involved to sensing and signaling in contrast with the basal root which appears to be implicate in nitrate acquisition.

Cross-Regulation between N Metabolism and Nitric Oxide (NO) Signaling during Plant Immunity

Plants are sessile organisms that have evolved a complex immune system which helps them cope with pathogen attacks. However, the capacity of a plant to mobilize different defense responses is strongly affected by its physiological status. Nitrogen (N) is a major nutrient that can play an important role in plant immunity by increasing or decreasing plant resistance to pathogens. Although no general rule can be drawn about the effect of N availability and quality on the fate of plant/pathogen interactions, plants' capacity to acquire, assimilate, allocate N, and maintain amino acid homeostasis appears to partly mediate the effects of N on plant defense. Nitric oxide (NO), one of the products of N metabolism, plays an important role in plant immunity signaling. NO is generated in part through Nitrate Reductase (NR), a key enzyme involved in nitrate assimilation, and its production depends on levels of nitrate/nitrite, NR substrate/product, as well as on L-arginine and polyamine levels. Cross-regulation between NO signaling and N supply/metabolism has been evidenced. NO production can be affected by N supply, and conversely NO appears to regulate nitrate transport and assimilation. Based on this knowledge, we hypothesized that N availability partly controls plant resistance to pathogens by controlling NO homeostasis. Using the Medicago truncatula/Aphanomyces euteiches pathosystem, we showed that NO homeostasis is important for resistance to this oomycete and that N availability impacts NO homeostasis by affecting S-nitrosothiol (SNO) levels and S-nitrosoglutathione reductase activity in roots. These results could therefore explain the increased resistance we noted in N-deprived as compared to N-replete M. truncatula seedlings. They open onto new perspectives for the studies of N/plant defense interactions.

Emerging Roles of Strigolactones in Plant Responses to Stress and Development

Our environment constantly undergoes changes either natural or manmade affecting growth and development of all the organisms including plants. Plants are sessile in nature and therefore to counter environmental changes such as light, temperature, nutrient and water availability, pathogen, and many others; plants have evolved intricate signaling mechanisms, composed of multiple components including several plant hormones. Research conducted in the last decade has placed Strigolactones (SLs) in the growing list of plant hormones involved in coping with environmental changes. SLs are carotenoid derivatives functioning as both endogenous and exogenous signaling molecules in response to various environmental cues. Initially, SLs were discovered as compounds that are harmful to plants due to their role as stimulants in seed germination of parasitic plants, a more beneficial role in plant growth and development was uncovered much later. SLs are required for maintaining plant architecture by regulating shoot and root growth in response to various external stimuli including arbuscular mycorrhizal fungi, light, nutrients, and temperature. Moreover, a role for SLs has also been recognized during various abiotic and biotic stress conditions making them suitable target for generating genetically engineered crop plants with improved yield. This review discusses the biosynthesis of SLs and their regulatory and physiological roles in various stress conditions. Understanding of detailed signaling mechanisms of SLs will be an important factor for designing genetically modified crops for overcoming the problem of crop loss under stressful conditions.

An efficient virus-induced gene silencing vector for maize functional genomics research

Maize is a major crop whose rich genetic diversity provides an advanced resource for genetic research. However, a tool for rapid transient gene function analysis in maize that may be utilized in most maize cultivars has been lacking, resulting in reliance on time-consuming stable transformation and mutation studies to obtain answers. We developed an efficient virus-induced gene silencing (VIGS) vector for maize based on a naturally maize-infecting cucumber mosaic virus (CMV) strain, ZMBJ-CMV. An infectious clone of ZMBJ-CMV was constructed, and a vascular puncture inoculation method utilizing Agrobacterium was optimized to improve its utility for CMV infection of maize. ZMBJ-CMV was then modified to function as a VIGS vector. The ZMBJ-CMV vector induced mild to moderate symptoms in many maize lines, making it useful for gene function studies in critically important maize cultivars, such as the sequenced reference inbred line B73. Using this CMV VIGS system, expression of two endogenous genes, ZmPDS and ZmIspH, was found to be decreased by 75% and 78%, respectively, compared with non-silenced tissue. Inserts with lengths of 100-300 bp produced the most complete transcriptional and visual silencing phenotypes. Moreover, genes related to autophagy, ZmATG3 and ZmATG8a, were also silenced, and it was found that they function in leaf starch degradation. These results indicate that our ZMBJ-CMV VIGS vector provides a tool for rapid and efficient gene function studies in maize.

The Response of the Root Apex in Plant Adaptation to Iron Heterogeneity in Soil

Iron (Fe) is an essential micronutrient for plant growth and development, and is frequently limiting. By contrast, over-accumulation of Fe in plant tissues leads to toxicity. In soils, the distribution of Fe is highly heterogeneous. To cope with this heterogeneity, plant roots engage an array of adaptive responses to adjust their morphology and physiology. In this article, we review root morphological and physiological changes in response to low- and high-Fe conditions and highlight differences between these responses. We especially focus on the role of the root apex in dealing with the stresses resulting from Fe shortage and excess.

Nitric Oxide-Mediated Maize Root Apex Responses to Nitrate are Regulated by Auxin and Strigolactones

Nitrate (NO3 (-)) is a key element for crop production but its levels in agricultural soils are limited. Plants have developed mechanisms to cope with these NO3 (-) fluctuations based on sensing nitrate at the root apex. Particularly, the transition zone (TZ) of root apex has been suggested as a signaling-response zone. This study dissects cellular and molecular mechanisms underlying NO3 (-) resupply effects on primary root (PR) growth in maize, confirming nitric oxide (NO) as a putative modulator. Nitrate restoration induced PR elongation within the first 2 h, corresponding to a stimulation of cell elongation at the basal border of the TZ. Xyloglucans (XGs) immunolocalization together with Brefeldin A applications demonstrated that nitrate resupply induces XG accumulation. This effect was blocked by cPTIO (NO scavenger). Transcriptional analysis of ZmXET1 confirmed the stimulatory effect of nitrate on XGs accumulation in cells of the TZ. Immunolocalization analyses revealed a positive effect of nitrate resupply on auxin and PIN1 accumulation, but a transcriptional regulation of auxin biosynthesis/transport/signaling genes was excluded. Short-term nitrate treatment repressed the transcription of genes involved in strigolactones (SLs) biosynthesis and transport, mainly in the TZ. Enhancement of carotenoid cleavage dioxygenases (CCDs) transcription in presence of cPTIO indicated endogenous NO as a negative modulator of CCDs activity. Finally, treatment with the SLs-biosynthesis inhibitor (TIS108) restored the root growth in the nitrate-starved seedlings. Present report suggests that the NO-mediated root apex responses to nitrate are accomplished in cells of the TZ via integrative actions of auxin, NO and SLs.

Reactive Oxygen Species and Nitric Oxide Control Early Steps of the Legume - Rhizobium Symbiotic Interaction

The symbiotic interaction between legumes and nitrogen-fixing rhizobium bacteria leads to the formation of a new organ, the nodule. Early steps of the interaction are characterized by the production of bacterial Nod factors, the reorientation of root-hair tip growth, the formation of an infection thread (IT) in the root hair, and the induction of cell division in inner cortical cells of the root, leading to a nodule primordium formation. Reactive oxygen species (ROS) and nitric oxide (NO) have been detected in early steps of the interaction. ROS/NO are determinant signals to arbitrate the specificity of this mutualistic association and modifications in their content impair the development of the symbiotic association. The decrease of ROS level prevents root hair curling and ITs formation, and that of NO conducts to delayed nodule formation. In root hairs, NADPH oxidases were shown to produce ROS which could be involved in the hair tip growth process. The use of enzyme inhibitors suggests that nitrate reductase and NO synthase-like enzymes are the main route for NO production during the early steps of the interaction. Transcriptomic analyses point to the involvement of ROS and NO in the success of the infection process, the induction of early nodulin gene expression, and the repression of plant defense, thereby favoring the establishment of the symbiosis. The occurrence of an interplay between ROS and NO was further supported by the finding of both S-sulfenylated and S-nitrosylated proteins during early symbiotic interaction, linking ROS/NO production to a redox-based regulation of the symbiotic process.

Cell Wall Heterogeneity in Root Development of Arabidopsis

Plant cell walls provide stability and protection to plant cells. During growth and development the composition of cell walls changes, but provides enough strength to withstand the turgor of the cells. Hence, cell walls are highly flexible and diverse in nature. These characteristics are important during root growth, as plant roots consist of radial patterns of cells that have diverse functions and that are at different developmental stages along the growth axis. Young stem cell daughters undergo a series of rapid cell divisions, during which new cell walls are formed that are highly dynamic, and that support rapid anisotropic cell expansion. Once the cells have differentiated, the walls of specific cell types need to comply with and support different cell functions. For example, a newly formed root hair needs to be able to break through the surrounding soil, while endodermal cells modify their walls at distinct positions to form Casparian strips between them. Hence, the cell walls are modified and rebuilt while cells transit through different developmental stages. In addition, the cell walls of roots readjust to their environment to support growth and to maximize nutrient uptake. Many of these modifications are likely driven by different developmental and stress signaling pathways. However, our understanding of how such pathways affect cell wall modifications and what enzymes are involved remain largely unknown. In this review we aim to compile data linking cell wall content and re-modeling to developmental stages of root cells, and dissect how root cell walls respond to certain environmental changes.

Plant Survival in a Changing Environment: The Role of Nitric Oxide in Plant Responses to Abiotic Stress

Nitric oxide in plants may originate endogenously or come from surrounding atmosphere and soil. Interestingly, this gaseous free radical is far from having a constant level and varies greatly among tissues depending on a given plant's ontogeny and environmental fluctuations. Proper plant growth, vegetative development, and reproduction require the integration of plant hormonal activity with the antioxidant network, as well as the maintenance of concentration of reactive oxygen and nitrogen species within a narrow range. Plants are frequently faced with abiotic stress conditions such as low nutrient availability, salinity, drought, high ultraviolet (UV) radiation and extreme temperatures, which can influence developmental processes and lead to growth restriction making adaptive responses the plant's priority. The ability of plants to respond and survive under environmental-stress conditions involves sensing and signaling events where nitric oxide becomes a critical component mediating hormonal actions, interacting with reactive oxygen species, and modulating gene expression and protein activity. This review focuses on the current knowledge of the role of nitric oxide in adaptive plant responses to some specific abiotic stress conditions, particularly low mineral nutrient supply, drought, salinity and high UV-B radiation.

Making better maize plants for sustainable grain production in a changing climate

Achieving grain supply security with limited arable land is a major challenge in the twenty-first century, owing to the changing climate and increasing global population. Maize plays an increasingly vital role in global grain production. As a C4 plant, maize has a high yield potential. Maize is predicted to become the number one cereal in the world by 2020. However, maize production has plateaued in many countries, and hybrid and production technologies have been fully exploited. Thus, there is an urgent need to shape maize traits and architectures for increased stress tolerance and higher yield in a changing climate. Recent achievements in genomics, proteomics, and metabolomics have provided an unprecedented opportunity to make better maize. In this paper, we discuss the current challenges and potential of maize production, particularly in China. We also highlight the need for enhancing maize tolerance to drought and heat waves, summarize the elite shoot and root traits and phenotypes, and propose an ideotype for sustainable maize production in a changing climate. This will facilitate targeted maize improvement through a conventional breeding program combined with molecular techniques.

Role of ethylene in responses of plants to nitrogen availability

Ethylene is a plant hormone involved in several physiological processes and regulates the plant development during the whole life. Stressful conditions usually activate ethylene biosynthesis and signaling in plants. The availability of nutrients, shortage or excess, influences plant metabolism and ethylene plays an important role in plant adaptation under suboptimal conditions. Among the plant nutrients, the nitrogen (N) is one the most important mineral element required for plant growth and development. The availability of N significantly influences plant metabolism, including ethylene biology. The interaction between ethylene and N affects several physiological processes such as leaf gas exchanges, roots architecture, leaf, fruits, and flowers development. Low plant N use efficiency (NUE) leads to N loss and N deprivation, which affect ethylene biosynthesis and tissues sensitivity, inducing cell damage and ultimately lysis. Plants may respond differently to N availability balancing ethylene production through its signaling network. This review discusses the recent advances in the interaction between N availability and ethylene at whole plant and different organ levels, and explores how N availability induces ethylene biology and plant responses. Exogenously applied ethylene seems to cope the stress conditions and improves plant physiological performance. This can be explained considering the expression of ethylene biosynthesis and signaling genes under different N availability. A greater understanding of the regulation of N by means of ethylene modulation may help to increase NUE and directly influence crop productivity under conditions of limited N availability, leading to positive effects on the environment. Moreover, efforts should be focused on the effect of N deficiency or excess in fruit trees, where ethylene can have detrimental effects especially during postharvest.