Understanding how chickpea responds to variable nitrate supply across their growing cycle will help to define breeding strategies to improve the nitrogen use efficiency (NUE) of this important legume crop. We repeatedly measured the rate of nitrate uptake in chickpea plants grown under low (LN:0.5 mM) or high (HN:5mM) nitrate solutions over a developmental time scale (vegetative to reproductive) using a semi-hydroponic growth system. For each N treatment, plant nitrate uptake capacity, growth and gene expression of putative high and low affinity nitrogen transporters and N-linked transcription factors were profiled across ten developmental stages from seedling to pod set. Plants with adequate N supply showed increased nitrate flux, which then declined during flowering and pod set stages. In contrast, a reversed trend was seen for N starved plants, where nitrate flux was low initially but gradually increased and then remained constant throughout later developmental stages. A significant increase in net nitrate uptake was observed for both treatments across the chickpea life cycle. Transcript abundance of a putative low affinity CaNPF6.3 correlated with root NO3- uptake capacity under adequate N supply, suggesting a role during vegetative growth stages. A reduction in NO3- supply during the lifecycle led to a dramatic increase in NO3- uptake capacity during flowering and pod set, a physiological event which preceded changes in transcript levels of both NRT2.1 and NRT2.4. These findings provide insight into nitrate uptake pathway across life cycle which is important in devising strategies to improve nitrogen use efficiencies.

GmbHLHm1 is a basic Helix-Loop-Helix membrane (bHLHm1) DNA binding transcription factor localized to the symbiosome membrane and nucleus in soybean (Glycine max ) nodules. Overexpression of GmbHLHm1 significantly increased nodule number and size, nitrogen fixation activity,and nitrogen delivery to the shoots. This contrasts with reduced nodule numbers per plant, nitrogen fixation activity and poor plant growth when silenced using RNAi. The promoter of GmbHLHm1 was found to be sensitive to exogenous GA supply, decreasing the level of GUS expression in transformed hairy roots in both nodules and roots and reducing native GmbHLHm1 expression in wild-type nodules. In summary, our study suggests that GmbHLHm1 positively regulates soybean nodulation and nitrogen fixation, and that GA can negatively regulate GmbHLHm1 expression in soybean nodules.

Chickpeas are a globally crucial agricultural product, currently at risk due to human-induced climate change. There has been little research into the impact of heat stress on chickpea compared to other crops, but it is known that heat stress can cause up to 100% yield loss. This study measures Growing Degree Days (GDD) in chickpeas, utilizing an existing calculation. This formula has been expanded for heat stress, titled Stress Degree Days (SDD), to examine the effects of high temperature stress on commercially important traits such as yield and seed size. Using a multi-environment trial, traits such as time to flowering, and seed size were observed in 148 chickpea cultivars across two sowing times in two different Australian locations (Narrabri in New South Wales, and Kununurra in Western Australia). It was determined that there is a significant correlation between yield, GDD, and SDD at all locations, sowing times, and life stages of the crop. These metrics allowed greater differentiation between environments when compared to a count of the number of calendar days required for each cultivar to reach a set life stage (flowering and maturation), allowing more accurate investigation the impacts of high temperature stress. It was also determined that loss of yield and a decrease in seed size was significantly correlated with high GDD and SDD, though seed size had less environmental plasticity (variability) compared to yield, and therefore higher stability under stress. GDD and SDD were shown to be useful for predicting genotype adaptation to locations and seasons thus providing a basis for varietal recommendations. This information could also be used to breed environment specific cultivars and to understand trait plasticity.

Sugars are essential for plant development, with nitrogen (N) availability playing a critical role in their distribution across plant organs, ultimately shaping growth patterns. However, the regulatory mechanisms modulating carbon (C) assimilate allocation and utilization under different N forms are not well understood. This study examined C fixation, utilization, and spatial re-distribution in the roots of hydroponically grown maize seedlings subjected to four N treatments: 1 mM NO3− (low N; LN), 2 mM NO3− (medium N; MN), 10 mM NO3− (high N; HN), and 1 mM NH4+ (low ammonium; LA). LN treatment significantly increased soluble sugar, sucrose, and starch contents while promoting greater root biomass at the expense of shoot biomass, leading to a higher root to shoot assimilate allocation. The activities of sugar and starch metabolism enzymes were more tightly regulated under LN, indicating enhanced C utilization and increased competition for assimilates. Key genes involved in sugar (ZmSPS, ZmSuSy, ZmSWEET6, ZmSUC2, ZmSTP2, and ZmAINV1) and starch (ZmAGPASE and ZmSS) metabolism were upregulated under LN, correlating with increased root sucrose and starch accumulation and enhanced enzyme activity. Sucrose and starch accumulated predominantly in the brace and lateral roots. This pattern suggests that excess C accumulation results from inefficient C utilization in sink tissues rather than impaired C assimilation. These findings provide new insights into how LN modulates C partitioning in roots for stress adaptation, highlighting the importance of improving C utilization in sink tissues to mitigate N deficiency and enhance plant growth.

Plants depend on nitrogen (N) to support their growth, development, and essential metabolic activities. However, the mechanisms modulating the distribution of N assimilates under supplemental N (SN) condition is unknown. This study examines carbon (C) metabolism and spatial distribution in maize seedlings subjected to three N treatments (T1 to T3): T1, 1 mM NO₃⁻ (low N, LN); T2, supplementation of 1 mM NO₃⁻ with 2 mM NO₃⁻ (1 mM NO₃⁻ → 2 mM NO₃⁻, SN); and T3, 2 mM NO₃⁻ (medium N, MN). SN treatment induced significant physiological and molecular adaptations, such as enhanced growth and total biomass under fluctuating N conditions. SN-treated plants exhibited enhanced photosynthetic activity and significantly greater accumulation of soluble sugars, sucrose, and starch compared to those under LN and MN treatments. Activities of key C metabolism enzymes, such as sucrose phosphate synthase (SPS), sucrose synthase (SuSy) and invertases (INVs), starch synthase (SS), AGPase, α-amylase (AMY) and β-amylase (BAM) were significantly upregulated, supporting efficient C metabolism. Molecular analysis revealed transcriptional reprogramming under SN, marked by the upregulation of genes related to sucrose (ZmSPS1, ZmSuSy1, ZmINVs, ZmSUT2, ZmSTP2, ZmSUC2 and ZmSWEET14) and starch (ZmSS1, ZmAGPase1, ZmAMY1 and ZmBAM1) metabolism and transport. The spatial and diurnal analysis revealed dynamic C partitioning and adaptive regulation, with SN plants maintaining higher sucrose and starch levels in the leaves, sheath and roots. These findings highlight the robust plasticity of maize C metabolism under SN conditions and provide valuable insights into optimizing nitrogen use efficiency (NUE) for sustainable crop production. Future studies will focus on exploring these adaptive mechanisms across different maize genotypes and under field conditions to improve NUE and productivity in varying N environments.

Nitrogen (N) deficiency in maize regulates carbon (C) metabolism by enhancing sugar and starch metabolism and related gene expression in both shoots and roots, while increasing root competition for assimilates causing carbohydrate accumulation in leaves and sheaths due reduced translocation to sink tissues. Soluble sugars are vital for plant development, with nitrogen (N) availability playing a key role in their distribution across plant organs, ultimately shaping growth patterns. However, the regulatory mechanisms governing carbon (C) assimilate allocation and utilization under different N forms remain unclear. This study examined C fixation, utilization, and spatial distribution in hydroponically grown maize seedlings subjected to four N treatments: 1 mM NO3⁻ (low N, LN), 2 mM NO3⁻ (medium N), 10 mM NO3⁻ (high N), and 1 mM NH4⁺ (low ammonium, LA). LN treatment significantly increased soluble sugar and starch contents while promoting greater root biomass at the expense of shoot biomass, leading to a higher root-to-shoot assimilate allocation. The activities of sugar and starch metabolism enzymes were more tightly regulated in both shoots and roots under LN, indicating enhanced C utilization and increased competition for assimilates, particularly in the root. Key genes involved in above-ground sugar and starch metabolism, ZmSPS1, ZmSuSy1, ZmCINV1, ZmVINV1, ZmCWINV1, ZmSTP2, ZmSUC2, ZmSWEET14, ZmSS1, ZmAMY1, ZmBAM1, and ZmAGPase1, were upregulated under LN, correlating with enhanced enzyme activity and resulting increased sugar and starch accumulation. Starch and sucrose accumulated more in LN-treated leaves than in other N treatments, with starch primarily stored in leaf tips and sucrose concentrated in the leaf sheath. This pattern suggests that excess C accumulation results from inefficient C utilization in sink tissues rather than impaired C assimilation. These findings provide new insights into how LN modulates C partitioning between leaves and roots for stress adaptation, highlighting the importance of improving C utilization in sink tissues to mitigate N deficiency and enhance plant growth.

Background and aims Biological nitrogen fixation (BNF) is central to long-term pedogenesis and overall terrestrial ecosystem development. Rates of asymbiotic BNF are potentially constrained by carbon (C), phosphorus (P), and/or nitrogenase cofactor elements (e.g., iron [Fe], vanadium [V], and molybdenum [Mo]), but our understanding of the biogeochemical trajectories of cofactor elements throughout pedogenesis is limited. Methods Using a similar to 700 ka pedogenic chronosequence at Cooloola in eastern Australia, we quantified P, Fe, V, and Mo in soil and litter and tested for C (i.e., energy), P, and/or Mo limitation of asymbiotic BNF using acetylene reduction assays. Results Cofactor elements in soil declined faster than P during pedogenesis, and their relative extractability with chelating agents increased across the chronosequence. Addition of C, P, and/or Mo did not affect asymbiotic BNF in any dune system tested. Conclusion Declines of soil P and cofactor elements during pedogenesis support an underlying influence of weathering on the biogeochemical cycling of these elements. However, dynamics of Fe, V, and Mo diverge from those of P due to increasing chelation by SOM as podzolization advances, whereas P is increasingly present in organic forms. Asymbiotic BNF is seemingly not limited by C, P, or Mo during pedogenesis at Cooloola.

Nitrogen (N) is a key macronutrient required for plant growth and reproduction. Ammonium (NH4+) is a readily available nitrogen source for plant growth and an important contributor to net plant nitrogen uptake and utilisation. It is suggested that members of the high-affinity ammonium transporter family (AMT) and the low-affinity ammonium major facilitator (AMF, non-AMT type) NH4+ transporters operate respectively as high-affinity (HATS) and low-affinity (LATS) transport pathways, both contributing to the management of overall plant NH4+ transport, uptake and cellular redistribution. In this chapter, we will examine NH4+ transport systems operating across different plant cell types and tissues in both a N2-fixing legume root nodule and in the model plant, Arabidopsis thaliana.

With recent climatic changes, the reduced access to solar radiation has become an emerging threat to chickpeas’ drought tolerance capacity under rainfed conditions. This study was conducted to assess, and understand the effects of reduced light intensity and quality on plant morphology, root development, and identifying resistant sources from a Sonali/PBA Slasher mapping population. We evaluated 180 genotypes, including recombinant inbred lines (RILs), parents, and commercial checks, using a split-block design with natural and low light treatments. Low light conditions, created by covering one of the two benches inside two growth chambers with a mosquito net, reduced natural light availability by approximately 70%. Light measurements encompassed photosynthetic photon flux density, as well as red, and far-red light readings taken at various stages of the experiment. The data, collected from plumule emergence to anthesis initiation, encompassed various indices relevant to root, shoot, and carbon gain (biomass). Statistical analysis examined variance, treatment effects, heritability, correlations, and principal components (PCs). Results demonstrated significant reductions in root biomass, shoot biomass, root/shoot ratio, and plant total dry biomass under suboptimal light conditions by 52.8%, 28.2%, 36.3%, and 38.4%, respectively. Plants also exhibited delayed progress, taking 9.2% longer to produce their first floral buds, and 19.2% longer to commence anthesis, accompanied by a 33.4% increase in internodal lengths. A significant genotype-by-environment interaction highlighted differing genotypic responses, particularly in traits with high heritability (> 77.0%), such as days to anthesis, days to first floral bud, plant height, and nodes per plant. These traits showed significant associations with drought tolerance indicators, like root, shoot, and plant total dry biomass. Genetic diversity, as depicted in a genotype-by-trait biplot, revealed contributions to PC1 and PC2 coefficients, allowing discrimination of low-light-tolerant RILs, such as 1_52, 1_73, 1_64, 1_245, 1_103, 1_248, and 1_269, with valuable variations in traits of interest. These RILs could be used to breed desirable chickpea cultivars for sustainable production under water-limited conditions. This study concludes that low light stress disrupts the balance between root and shoot morphology, diverting photosynthates to vegetative structures at the expense of root development. Our findings contribute to a better understanding of biomass partitioning under limited-light conditions, and inform breeding strategies for improved drought tolerance in chickpeas.

ABSTRACTChickpeas are well adapted to rainfed conditions, but a lack of moisture during the reproductive phase can result in lower pod setting and ultimately reduced grain yield. The exact reasons for this reduction are not fully understood, partly because of the lack of information on soil moisture content (SMC) and water use during podding. This study aimed to address this knowledge gap by quantifying the impact of gradual drought on various yield components of desi‐type genotypes using the fraction of transpirable soil water (FTSW) method. Two water treatments were applied at the start of anthesis: well‐watered (WW) and drought‐stressed (DS). The WW was maintained at 24% SMC, whereas the DS was dried to 3% SMC. The results showed that DS caused early podding (3.3 days less), with reductions in plant height (11.4 cm), leaf area (1249.5 cm2), flowers (18.6), pods (27.4), seeds (37.0), grain yield (0.2 g), aboveground dry biomass (11.4 g) and harvest index (0.2 g), while increasing flower abortion (14.6) and seed biomass (1.5 g). However, diverse genotypic responses were observed to treatments, as well as water usage, FTSW and SMC that triggered pods which ranged from 1.12 to 1.89 L, 0.05 to 0.43 and 4.0% to 12.2%, respectively. A positive association between days taken and the amount of water used to terminate pods indicated that quicker‐triggering genotypes, such as Rupali and Genesis 836, consumed less water to develop pods than Flipper, ICCV_06109 and PBA Slasher did. Conversely, the negative association between the amount of water used and the number of pods triggered, seeds and grain yield explained the superior performance of Rupali and Genesis 836. These genotypes extracted less water (FTSW = 0.36 and 0.43; SMC = 10.3% and 12.2%, respectively) to develop pods and maintained favourable photosynthesis at lower transpiration rates for longer periods, allowing them to use residual moisture more efficiently. Our research offers crucial insights that can be beneficial to breeders and physiologists, paving the way for future studies aimed at developing drought‐tolerant genotypes.

Chickpeas are a vital source of protein and starch for a large portion of the world’s population and are known to be impacted by heat stress at every life stage. Previously known as an “Orphan Legume”, little is known of the genetic control of heat stress tolerance, and most previous research has focused on heat avoidance rather than tolerance. This study utilised a population of 148 chickpea genotypes, primarily Kabulis, in 12 field trials conducted at 2 locations, two sowing periods, and across 3 years. Physiology was examined, and data was paired with Diversity Arrays Technology (DArT) sequencing to perform a Genome Wide Association Study to connect phenotypic and genotypic regions. Fourteen QTL related to yield, seed size, time to flowering, time to maturity, and final canopy closure were found. Among these, are the first Quantitative Trait Loci (QTL) ever identified for canopy closure in chickpea, along with a QTL that is likely linked to early flowering under heat stress. Early flowering in this case refers to a cultivar flowering significantly earlier than the others in the genotype set. Additionally, several other QTL provide validation of previous research. These QTL hotspots that can be targeted for selective breeding of several traits concurrently. Overall, new targets for genome assisted breeding for heat tolerance in chickpea were identified and can be utilised by the breeder community to improve the status of selective breeding for heat tolerance in this crop.

Aims To assess the symbiotic effectiveness, tolerance to abiotic stress factors and phosphate solubilizing ability of new chickpea root-nodule bacteria. Methods Symbiotic effectiveness, abiotic stress tolerance and phosphate solubilizing ability of ten new chickpea rhizobial strains collected from soils were evaluated using laboratory and glasshouse experiments. Results Six of the ten strains were symbiotically efficient with diversity between those and the commercial chickpea strain CC1192. High temperatures significantly affected strain survival in liquid and peat carrier. Peat carrier offered greater protection. Above 37 °C, strain infectivity decreased with no correlation between strain origin and their infectivity after exposure. Three of the new strains and CC1192 produced optimum growth and survival at pH 6.8 and at two lower pH’s of 4.4 and 5.4 were able to neutralize the growth medium while the other seven strains at high pH were able to either neutralize or acidify the growth medium. Strain survival was significantly higher at increased salt concentrations of NaCl compared to CaCl 2 . At 3% NaCl concentration, 8 strains survived while at 3% CaCl 2 only 3 survived . Many strains were resistant to more than one antibiotic. All strains were able to solubilize phosphate. The ratio between the most efficient strain and the least was 3:1. Conclusions Chickpea rhizobia strains sourced from soils in Narrabri New South Wales and Kununurra in Western Australia differed in expressed traits from the commercial strain CC1192. These unique traits could provide additional tools for rhizobial strain selection to benefit chickpea production in different soil environments.

This article is a Commentary on Cassan et al . (2023), 239 : 992–1004 .

Chickpea is the second-most-cultivated legume globally, with India and Australia being the two largest producers. In both of these locations, the crop is sown on residual summer soil moisture and left to grow on progressively depleting water content, finally maturing under terminal drought conditions. The metabolic profile of plants is commonly, correlatively associated with performance or stress responses, e.g., the accumulation of osmoprotective metabolites during cold stress. In animals and humans, metabolites are also prognostically used to predict the likelihood of an event (usually a disease) before it occurs, e.g., blood cholesterol and heart disease. We sought to discover metabolic biomarkers in chickpea that could be used to predict grain yield traits under terminal drought, from the leaf tissue of young, watered, healthy plants. The metabolic profile (GC-MS and enzyme assays) of field-grown chickpea leaves was analysed over two growing seasons, and then predictive modelling was applied to associate the most strongly correlated metabolites with the final seed number plant−1. Pinitol (negatively), sucrose (negatively) and GABA (positively) were significantly correlated with seed number in both years of study. The feature selection algorithm of the model selected a larger range of metabolites including carbohydrates, sugar alcohols and GABA. The correlation between the predicted seed number and actual seed number was R2 adj = 0.62, demonstrating that the metabolic profile could be used to predict a complex trait with a high degree of accuracy. A previously unknown association between D-pinitol and hundred-kernel weight was also discovered and may provide a single metabolic marker with which to predict large seeded chickpea varieties from new crosses. The use of metabolic biomarkers could be used by breeders to identify superior-performing genotypes before maturity is reached.

Root systems of most land plants are colonised by arbuscular mycorrhiza fungi. The symbiosis supports nutrient acquisition strategies predominantly associated with plant access to inorganic phosphate. The nutrient acquisition is enhanced through an extensive network of external fungal hyphae that extends out into the soil, together with the development of fungal structures forming specialised interfaces with root cortical cells. Orthologs of the bHLHm1;1 transcription factor, previously described in soybean nodules (GmbHLHm1) and linked to the ammonium facilitator protein GmAMF1;3, have been identified in Medicago (Medicago truncatula) roots colonised by AM fungi. Expression studies indicate that transcripts of both genes are also present in arbuscular containing root cortical cells and that the MtbHLHm1;1 shows affinity to the promoter of MtAMF1;3. Both genes are induced by AM colonisation. Loss of Mtbhlhm1;1 expression disrupts AM arbuscule abundance and the expression of the ammonium transporter MtAMF1;3. Disruption of Mtamf1;3 expression reduces both AM colonisation and arbuscule development. The respective activities of MtbHLHm1;1 and MtAMF1;3 highlight the conservation of putative ammonium regulators supporting both the rhizobial and AM fungal symbiosis in legumes.

Main conclusionLegumes manage both symbiotic (indirect) and non-symbiotic (direct) nitrogen acquisition pathways. Understanding and optimising the direct pathway for nitrate uptake will support greater legume growth and seed yields.Legumes have multiple pathways to acquire reduced nitrogen to grow and set seed. Apart from the symbiotic N-2-fixation pathway involving soil-borne rhizobia bacteria, the acquisition of nitrate and ammonia from the soil can also be an important secondary nitrogen source to meet plant N demand. The balance in N delivery between symbiotic N (indirect) and inorganic N uptake (direct) remains less clear over the growing cycle and with the type of legume under cultivation. In fertile, pH balanced agricultural soils, NO3- is often the predominant form of reduced N available to crop plants and will be a major contributor to whole plant N supply if provided at sufficient levels. The transport processes for NO3- uptake into legume root cells and its transport between root and shoot tissues involves both high and low-affinity transport systems called HATS and LATS, respectively. These proteins are regulated by external NO3- availability and by the N status of the cell. Other proteins also play a role in NO3- transport, including the voltage dependent chloride/nitrate channel family (CLC) and the S-type anion channels of the SLAC/SLAH family. CLC's are linked to NO3- transport across the tonoplast of vacuoles and the SLAC/SLAH's with NO3- efflux across the plasma membrane and out of the cell. An important step in managing the N requirements of a plant are the mechanisms involved in root N uptake and the subsequent cellular distribution within the plant. In this review, we will present the current knowledge of these proteins and what is understood on how they function in key model legumes (Lotus japonicus, Medicago truncatula and Glycine sp.). The review will examine their regulation and role in N signalling, discuss how post-translational modification affects NO3- transport in roots and aerial tissues and its translocation to vegetative tissues and storage/remobilization in reproductive tissues. Lastly, we will present how NO(3)(-)influences the autoregulation of nodulation and nitrogen fixation and its role in mitigating salt and other abiotic stresses.

The cyanogenic glucoside, dhurrin, present in Sorghum bicolor is thought to have multiple functions, including in defence against herbivory. The hormone methyl jasmonate (MeJA) is also induced by herbivory and is key to instigating defence processes in plants. To investigate whether dhurrin is induced in response to herbivore attack and also to the associated presence of MeJA, sorghum plants were either wounded or exogenous MeJA was applied. We show that specific wounding (pin board and perforation) and the application of MeJA increases dhurrin concentration in leaves and sheath tissue 12 h after treatment. Quantitative PCR shows that the expression of two genes, SbCYP79A1 and SbUGT85B1, involved in the synthesis of dhurrin are significantly induced by exogenous MeJA and by wounding. Analysis of 2 kb of sequence upstream of the start codon of SbCYP79A1 identifies several cis-acting elements that have been linked to MeJA induction. A promoter deletion series, coupled to GFP, and transiently expressed in Nicotiana benthamiana suggests that there are potentially three sequence motifs (~-925 to -976) involved in the binding of transcription factors that result in increased expression of SbCYP79A1 and the synthesis of dhurrin in response to MeJA.

The root tip of a plant is highly sensitive to environmental cues and exerts sensory, chemical and movement responses and has even been likened to an animal’s brain. Yet, the assemblage of microbes at the root tip, the control of their diversity, the nature of their recruitment to that particular volume, and their roles in plant phenotypic function, remain poorly understood. This study investigated longitudinal niche differentiation of the root-associated microbiome in chickpeas ( Cicer arietinum L.) and its interactions with both diverse soil types and host plants with genetic variation in phenology, from the exterior to the interior of the root. Compared with late flowering (LF) genotypes, endophyte microbiomes at the apical zone of the early flowering (EF) host were characterised by greater diversity, higher compositional similarity to the basal zone, and closely inhabiting Rhizobacter and Methylotenera across soils. Additionally, EF genotypes secreted a specific composition of metabolites from the apical zone, with more carboxylates and amino acids (especially propionic acid and benzoic acid) than the LF plant. Our findings demonstrate that longitudinal differentiation within a seedling root is an essential feature shaping the root microbiome and indicative of genetic variation in phenology of host plants.

Chickpea is a globally important commercial crop and a key source of protein for vegetarian populations. Though chickpea was domesticated at least 3000 years ago, research into abiotic stress tolerance has been limited compared to cereal crops such as wheat. This review investigates the impacts of heat stress on chickpea, focusing on reproductive development. The fertilisation process is particularly sensitive to environmental stress, such as drought and heat that can reduce yields by up to 70%. Current research has largely focused on breeding cultivars that reach maturity faster to avoid stress rather than true thermotolerance and little is known of the impact of heat on cellular processes. This review suggests that there is ample variation within the chickpea gene pool for selective breeding to achieve improved abiotic stress tolerance. Rates of genetic progress will improve once key QTL are identified and the link between thermotolerance and pollen viability confirmed. Other benefits may arise from better understanding of heat shock proteins and molecular chaperones and their role in the protection of reproductive processes.

Nitrogen is an essential nutrient for plants, but crop plants are inefficient in the acquisition and utilization of applied nitrogen. This often results in producers over applying nitrogen fertilizers, which can negatively impact the environment. The development of crop plants with more efficient nitrogen usage is, therefore, an important research goal in achieving greater agricultural sustainability. We utilized genetically modified rice lines over-expressing a barley alanine aminotransferase ( HvAlaAT ) to help characterize pathways which lead to more efficient use of nitrogen. Under the control of a stress-inducible promoter OsAnt1 , OsAnt1:HvAlaAT lines have increased above-ground biomass with little change to both nitrate and ammonium uptake rates. Based on metabolic profiles, carbon metabolites, particularly those involved in glycolysis and the tricarboxylic acid (TCA) cycle, were significantly altered in roots of OsAnt1:HvAlaAT lines, suggesting higher metabolic turnover. Moreover, transcriptomic data revealed that genes involved in glycolysis and TCA cycle were upregulated. These observations suggest that higher activity of these two processes could result in higher energy production, driving higher nitrogen assimilation, consequently increasing biomass production. Other potential mechanisms contributing to a nitrogen-use efficient phenotype include involvements of phytohormonal responses and an alteration in secondary metabolism. We also conducted basic growth studies to evaluate the effect of the OsAnt1:HvAlaAT transgene in barley and wheat, which the transgenic crop plants increased seed production under controlled environmental conditions. This study provides comprehensive profiling of genetic and metabolic responses to the over-expression of AlaAT and unravels several components and pathways which contribute to its nitrogen-use efficient phenotype.