Root plasticity improves maize nitrogen use when nitrogen is limiting - an analysis using 3D plant modelling.

Plant phenotypic plasticity plays an important role in nitrogen (N) acquisition and use under nitrogen-limited conditions. However, this role has never been quantified as a function of N availability, leaving it unclear whether plastic responses should be considered as potential targets for selection. A combined modelling and experimentation approach was adopted to quantify the role of plasticity on N uptake and plant yield. Based on a greenhouse experiment we considered plasticity in two maize traits: root-to-leaf biomass allocation ratio and emergence rate of axial roots. In a simulation experiment we individually enabled or disabled both plastic responses for maize stands grown across six N levels. Both plastic responses contributed to maintaining a higher N uptake and plant productivity as N-availability declined, compared to stands in which plastic responses were disabled. We conclude that plastic responses quantified in this study may be a potential target trait in breeding programs for greater N uptake across N levels while it may only be important for the internal use of N under N-limited conditions in maize. Given the complexity of breeding for plastic responses, an a priori model analysis is useful to identify which plastic traits to target for enhanced plant performance.

Genomic basis determining root system architecture in maize.

KEY MESSAGE: A total of 389 and 344 QTLs were identified by GWAS and QTL mapping explaining accumulatively 32.2-65.0% and 23.7-63.4% of phenotypic variation for 14 shoot-borne root traits using more than 1300 individuals across multiple field trails. Efficient nutrient and water acquisition from soils depends on the root system architecture (RSA). However, the genetic determinants underlying RSA in maize remain largely unexplored. In this study, we conducted a comprehensive genetic analysis for 14 shoot-borne root traits using 513 inbred lines and 800 individuals from four recombinant inbred line (RIL) populations at the mature stage across multiple field trails. Our analysis revealed substantial phenotypic variation for these 14 root traits, with a total of 389 and 344 QTLs identified through genome-wide association analysis (GWAS) and linkage analysis, respectively. These QTLs collectively explained 32.2-65.0% and 23.7-63.4% of the trait variation within each population. Several a priori candidate genes involved in auxin and cytokinin signaling pathways, such as IAA26, ARF2, LBD37 and CKX3, were found to co-localize with these loci. In addition, a total of 69 transcription factors (TFs) from 27 TF families (MYB, NAC, bZIP, bHLH and WRKY) were found for shoot-borne root traits. A total of 19 genes including PIN3, LBD15, IAA32, IAA38 and ARR12 and 19 GWAS signals were overlapped with selective sweeps. Further, significant additive effects were found for root traits, and pyramiding the favorable alleles could enhance maize root development. These findings could contribute to understand the genetic basis of root development and evolution, and provided an important genetic resource for the genetic improvement of root traits in maize.

Carbon footprint of farming practices in farmland ecosystems on the North and Northeast China plains.

Fast development of farming practices in China is projected to result in additional carbon emissions and thus affect farmland ecosystems' environmental performance. Based on 454 farm surveys on the North and Northeast China Plain, the carbon footprint (CF) of two farmland ecosystems (irrigated system for wheat and maize on the North China Plain and rainfed system for maize on the Northeast Plain) were assessed and emission reduction pathways explored by quantifying greenhouse gas emissions of agricultural inputs and farm practices during the entire crop growing seasons with an agricultural footprint model. The results demonstrated that the GHG emissions from wheat and maize rotation in the irrigated system were 7.63 t CO2 eq ha-1 and 3.17 t CO2 eq ha-1 for single season maize in the rainfed system. While energy consumption accounted for 12.5%-21.3% of the carbon footprint in both systems, the group assessment found that the largest difference in GHG emissions between the high and low emission groups came from mechanical energy consumption. Approximately 50.6% and 39.2% of the mechanical carbon footprint of wheat and maize, respectively, were caused by irrigation practices in the irrigated system. Regarding the rainfed system, where 46.6% of mechanical carbon emissions were generated by maize tillage operations. In addition, scenario analysis indicated that the mechanical carbon footprint could be reduced to 56 kg CO2 eq t-1 for NCP-wheat and 26 kg CO2 eq t-1 for NCP-maize, respectively, by optimizing yields and irrigation practices in irrigated systems and that the mechanical carbon footprint of NEP-maize could be reduced to 25 kg CO2 eq t-1 by optimizing yields and tillage practices in rainfed systems. Therefore, improvement in mechanization in irrigation and tillage practices can contribute to reduce GHG emissions in China. Water-saving irrigation technology is recommended in irrigated area and conservation tillage is recommended in rainfed agricultural area to reduce carbon footprints.

Hybrid performance evaluation and genome-wide association analysis of root system architecture in a maize association population.

KEY MESSAGE: The genetic architecture of RSA traits was dissected by GWAS and coexpression networks analysis in a maize association population. Root system architecture (RSA) is a crucial determinant of water and nutrient uptake efficiency in crops. However, the maize genetic architecture of RSA is still poorly understood due to the challenges in quantifying root traits and the lack of dense molecular markers. Here, an association mapping panel including 356 inbred lines were crossed with a common tester, Zheng58, and the test crosses were phenotyped for 12 RSA traits in three locations. We observed a 1.3 ~ sixfold phenotypic variation for measured RSA in the association panel. The association panel consisted of four subpopulations, non-stiff stalk (NSS) lines, stiff stalk (SS), tropical/subtropical (TST), and mixed. Zheng58 × TST has a 2.1% higher crown root number (CRN) and 8.6% less brace root number (BRN) than Zheng58 × NSS and Zheng58 × SS, respectively. Using a genome-wide association study (GWAS) with 1.25 million SNPs and correction for population structure, 191 significant SNPs were identified for root traits. Ninety (47%) of the significant SNPs showed positive allelic effects, and 101 (53%) showed negative effects. Each locus could explain 0.39% to 11.8% of phenotypic variation. By integrating GWAS results and comparing coexpression networks, 26 high-priority candidate genes were identified. Gene GRMZM2G377215, which belongs to the COBRA-like gene family, affected root growth and development. Gene GRMZM2G468657 encodes the aspartic proteinase nepenthesin-1, related to root development and N-deficient response. Collectively, our research provides progress in the genetic dissection of root system architecture. These findings present the further possibility for the genetic improvement of root traits in maize.

Mining genes regulating root system architecture in maize based on data integration analysis.

KEY MESSAGE: A new strategy that integrated multiple public data resources was established to construct root gene co-expression network and mine genes regulating root system architecture in maize. A root gene co-expression network, containing 13,874 genes, was constructed. A total of 53 root hub genes and 16 priority root candidate genes were identified. One priority root candidate was further functionally verified using overexpression transgenic maize lines. Root system architecture (RSA) is crucial for crops productivity and stress tolerance. In maize, few RSA genes are functionally cloned, and effective discovery of RSA genes remains a great of challenge. In this work, we established a strategy to mine maize RSA genes by integrating functionally characterized root genes, root transcriptome, weighted gene co-expression network analysis (WGCNA) and genome-wide association analysis (GWAS) of RSA traits based on public data resources. A total of 589 maize root genes were collected by searching well-characterized root genes in maize or homologous genes of other species. We performed WGCNA to construct a maize root gene co-expression network containing 13874 genes based on public available root transcriptome data, and further discovered the 53 hub genes related to root traits. In addition, by the prediction function of obtained root gene co-expression network, a total of 1082 new root candidate genes were explored. By further overlapping the obtained new root candidate gene with the root-related GWAS of RSA candidate genes, 16 priority root candidate genes were identified. Finally, a priority root candidate gene, Zm00001d023379 (encodes pyruvate kinase 2), was validated to modulate root open angle and shoot-borne roots number using its overexpression transgenic lines. Our results develop an integration analysis method for effectively exploring regulatory genes of RSA in maize and open a new avenue to mine the candidate genes underlying complex traits.

Auxin efflux carrier ZmPIN1a modulates auxin reallocation involved in nitrate-mediated root formation.

BACKGROUND: Auxin plays a crucial role in nitrate (NO3-)-mediated root architecture, and it is still unclear that if NO3- supply modulates auxin reallocation for regulating root formation in maize (Zea mays L.). This study was conducted to investigate the role of auxin efflux carrier ZmPIN1a in the root formation in response to NO3- supply. RESULTS: Low NO3- (LN) promoted primary root (PR) elongation, while repressed the development of lateral root primordia (LRP) and total root length. LN modulated auxin levels and polar transport and regulated the expression of auxin-responsive and -signaling genes in roots. Moreover, LN up-regulated the expression level of ZmPIN1a, and overexpression of ZmPIN1a enhanced IAA efflux and accumulation in PR tip, while repressed IAA accumulation in LRP initiation zone, which consequently induced LN-mediated PR elongation and LR inhibition. The inhibition rate of PR length, LRP density and number of ZmPIN1a-OE plants was higher than that of wild-type plants after auxin transport inhibitor NPA treatment under NN and LN conditions, and the degree of inhibition of root growth in ZmPIN1a-OE plants was more obvious under LN condition. CONCLUSION: These findings suggest that ZmPIN1a was involved in modulating auxin levels and transport to alter NO3--mediated root formation in maize.

Impacts of maize hybrids with different nitrogen use efficiency on root-associated microbiota based on distinct rhizosphere soil metabolites.

Plant genotypes shape root-associated microbiota that affect plant nutrient acquisition and productivity. It is unclear how maize hybrids modify root-associated microbiota and their functions and relationship with nitrogen use efficiency (NUE) by regulating rhizosphere soil metabolites. Here, two N-efficient (NE) (ZD958, DMY3) and two N-inefficient (NIE) maize hybrids (YD9953, LY99) were used to investigate this issue under low N (60 kg N ha-1 , LN) and high N (180 kg N ha-1 , HN) field conditions. NE hybrids had higher yield than NIE hybrids under LN but not HN. NE and NIE hybrids recruited only distinct root-associated bacterial microbiota in LN. The bacterial network stability was stronger in NE than NIE hybrids. Compared with NIE hybrids, NE hybrids recruited more bacterial taxa that have been described as plant growth-promoting rhizobacteria (PGPR), and less related to denitrification and N competition; this resulted in low N2 O emission and high rhizosphere NO3 - -N accumulation. NE and NIE hybrids had distinct rhizosphere soil metabolite patterns, and their specific metabolites were closely related to microbiota and specific genera under LN. Our findings reveal the relationships among plant NUE, rhizosphere soil metabolites, root-associated microbiota, and soil nutrient cycling, and this information is informative for breeding NE crops.

Crop rotation increases root biomass and promotes the correlation of soil dissolved carbon with the microbial community in the rhizosphere.

As essential approaches for conservation agricultural practices, straw residue retention and crop rotation have been widely used in the Mollisols of Northeast China. Soil organic carbon, root development and microbial community are important indicators representing soil, crop and microbiota, respectively, and these factors work together to influence soil fertility and crop productivity. Studying their changes and interactions under different conservation practices is crucial to provide a theoretical basis for developing rational agricultural practices. The experiment in this study was conducted using the conventional practice (continuous maize without straw retention, C) and three conservation practices, namely, continuous maize with straw mulching (CS), maize-peanut rotation (R), and maize-peanut rotation with straw mulching (RS). Straw mulching (CS) significantly increased soil total organic carbon (TOC), active organic carbon (AOC), and microbial biomass carbon (MBC), but did not promote maize yield. Maize-peanut rotation (R and RS) significantly increased dissolved organic carbon (DOC) in the rhizosphere by promoting root growth, and maize yield (increased by 10.2%). For the microbial community structure, PERMANOVA and PCoA indicated that the bacterial community differed significantly between rhizosphere soil and bulk soil, but the fungal community shifted more under different agricultural practices. The correlation analysis indicated that the rotation system promoted the association between the soil DOC and the microbial community (especially the bacterial community), and straw mulching enhanced the connection between the soil TOC and the fungal community. Some plant growth-promoting rhizobacteria (including Bacillus, Streptomyces, Rhizobium, and Pseudomonas) were enriched in the rhizosphere soil and were increased in the rotation system (R and RS), which might be due to an increase in the soil rhizosphere DOC level. These beneficial microbes had significantly negative correlations with several fungal groups (such as Mycosphaerella, Penicillium, Paraphoma and Torula) that were classified as plant pathotrophs by FUNGuild. These results indicated that ensuring plant root development and improving root-bacteria interactions are of great importance to guarantee crop yield when implementing conservation tillage practices.

Genome-wide dissection of changes in maize root system architecture during modern breeding.

Appropriate root system architecture (RSA) can improve maize yields in densely planted fields, but little is known about its genetic basis in maize. Here we performed root phenotyping of 14,301 field-grown plants from an association mapping panel to study the genetic architecture of maize RSA. A genome-wide association study identified 81 high-confidence RSA-associated candidate genes and revealed that 28 (24.3%) of known root-related genes were selected during maize domestication and improvement. We found that modern maize breeding has selected for a steeply angled root system. Favourable alleles related to steep root system angle have continuously accumulated over the course of modern breeding, and our data pinpoint the root-related genes that have been selected in different breeding eras. We confirm that two auxin-related genes, ZmRSA3.1 and ZmRSA3.2, contribute to the regulation of root angle and depth in maize. Our genome-wide identification of RSA-associated genes provides new strategies and genetic resources for breeding maize suitable for high-density planting.

Comparative Transcriptome Analysis Reveals Common and Developmental Stage-Specific Genes That Respond to Low Nitrogen in Maize Leaves.

A growing leaf can be divided into three sections: division zone, elongation zone, and maturation zone. In previous studies, low nitrogen (LN) inhibited maize growth and development, especially leaf growth; however, the gene expression in response to LN in different regions in leaf were not clear. Here, using hydroponics and a transcriptome approach, we systematically analyzed the molecular responses of those zones and differentially expressed genes (DEG) in response to LN supply. Developmental stage-specific genes (SGs) were highly stage-specific and involved in distinct biological processes. SGs from division (SGs-DZ) and elongation zones (SGs-EZ) were more related to developmentally dependent processes, whereas SGs of the maturation zone (SGs-MZ) were more related to metabolic processes. The common genes (CGs) were overrepresented in carbon and N metabolism, suggesting that rebalancing carbon and N metabolism in maize leaves under LN condition was independent of developmental stage. Coexpression modules (CMs) were also constructed in our experiment and a total of eight CMs were detected. Most of SGs-DZ and SGs-EZ were classified into a set termed CM turquoise, which was mainly enriched in ribosome and DNA replication, whereas several genes from SGs-MZ and CGs were clustered into CM blue, which mainly focused on photosynthesis and carbon metabolism. Finally, a comprehensive coexpression network was extracted from CM blue, and several maize CONSTANS-LIKE(ZmCOL) genes seemed to participate in regulating photosynthesis in maize leaves under LN condition in a developmental stage-specific manner. With this study, we uncovered the LN-responsive CGs and SGs that are important for promoting plant growth and development under insufficient nitrogen supply.

Plasticity of root anatomy during domestication of a maize-teosinte derived population.

Maize (Zea mays L.) has undergone profound changes in root anatomy for environmental adaptation during domestication. However, the genetic mechanism of plasticity of maize root anatomy during the domestication process remains unclear. In this study, high-resolution mapping was performed for nine root anatomical traits using a maize-teosinte population (mexicana × Mo17) across three environments. Large genetic variations were detected for different root anatomical traits. The cortex, stele, aerenchyma areas, xylem vessel number, and cortical cell number had large variations across three environments, indicating high plasticity. Sixteen quantitative trait loci (QTL) were identified, including seven QTL with QTL × environment interaction (EIQTL) for high plasticity traits and nine QTL without QTL × environment interaction (SQTL). Most of the root loci were consistent with shoot QTL depicting domestication signals. Combining transcriptome and genome-wide association studies revealed that AUXIN EFFLUX CARRIER PIN-FORMED LIKE 4 (ZmPILS4) serves as a candidate gene underlying a major QTL of xylem traits. The near-isogenic lines (NILs) with lower expression of ZmPILS4 had 18-24% more auxin concentration in the root tips and 8-15% more xylem vessels. Nucleotide diversity values analysis in the promoter region suggested that ZmPILS4 was involved in maize domestication and adaptation. These results revealed the potential genetic basis of root anatomical plasticity during domestication.

A simple "turn off-on" ratio fluorescent probe for sensitive detection of dopamine and lysine/arginine.

Herein, a novel and unique "off-on" single-excited dual-emissive ratio fluorescence sensor for highly selective and sensitive detection of dopamine and lysine/arginine has been developed via covalently connecting the yellowish-green fluorescent carbon dots (CDs) with the orange-red fluorescent AgInSe2@ZnS quantum dots (AISe QDs). This ratiometric fluorescence sensor provided with two-emission peaks at 495 and 575 nm under a single-excitation wavelength of 395 nm. The fluorescence of AISe QDs (F575) is effective quenched by dopamine and only efficientlyrecovered by lysine/arginine; meanwhile, the light of CDs (F495) remains unchanged. The fluorescence intensity ratio (F495/F575) showed a linear relationship with the concentration of DA in the range of 0-100 µM, and the detection limit as low as 0.21 nM. lysine and arginine with the detection limit of 0.36 nM and 26 µM, respectively. Furthermore, the fluorescence probe is successfully used to detect DA in human serum. Therefore, the as-synthesized probe shows excellent potential application for the determination of DA in real samples.

Effectsof growth-promoting rhizobacteria on maize growth and rhizosphere microbial community under conservation tillage in Northeast China.

Conservation tillage in conjunction with straw mulching is a sustainable agricultural approach. However, straw mulching reduces the soil temperature, inhibits early maize growth and reduces grain yield in cold regions. To address this problem, we investigated the effects of inoculation of plant growth-promoting rhizobacteria (PGPR) on maize growth and rhizosphere microbial communities under conservation tillage in Northeast China. The PGPR strains Sinorhizobium sp. A15, Bacillus sp. A28, Sphingomonas sp. A55 and Enterobacter sp. P24 were isolated from the maize rhizosphere in the same area and inoculated separately. Inoculation of these strains significantly enhanced maize growth, and the strains A15, A28 and A55 significantly increased grain yield by as much as 22%-29%. Real-time quantitative PCR and high-throughput sequencing showed that separate inoculation with the four strains increased the abundance and species richness of bacteria in the maize rhizosphere. Notably, the relative abundance of Acidobacteria_Subgroup_6, Chloroflexi_KD4-96, and Verrucomicrobiae at the class level and Mucilaginibacter at the genus level were positively correlated with maize biomass and yield. Inoculation with PGPR shows potential for improvement of maize production under conservation tillage in cold regions by regulating the rhizosphere bacterial community structure and by direct stimulation of plant growth.

Synergistic Regulation of Nitrogen and Sulfur on Redox Balance of Maize Leaves and Amino Acids Balance of Grains.

As a primary food crop, maize is widely grown around the world. However, the deficiency of essential amino acids, such as lysine, tryptophan, and methionine, results in poor nutritional quality of maize. In addition, the protein concentration of maize declines with the increase in yield, which further reduces the nutritional quality. Here, the photosynthesis of leaves, grain amino acid composition, and stoichiometry of N and S are explored. The results show that N and S maintained the redox balance by increasing the content of glutathione in maize leaves, thereby enhancing the photosynthetic rate and maize yield. Simultaneously, the synergy of N and S increased the grain protein concentration and promoted amino acid balance by increasing the cysteine concentration in maize grains. The maize yield, grain protein concentration, and concentration of essential amino acids, such as lysine, tryptophan, and methionine, could be simultaneously increased in the N:S ratio range of 11.0 to 12.0. Overall, the synergy of N and S simultaneously improved the maize yield and nutritional quality by regulating the redox balance of maize leaves and the amino acids balance of grains, which provides a new theoretical basis and practical method for sustainable production of maize.

Low nitrogen induces root elongation via auxin-induced acid growth and auxin-regulated target of rapamycin (TOR) pathway in maize.

Under low nitrogen (N) supply, an important adaption of the maize root system is to promote the root elongation so as to increase N uptake from a larger soil space. The underlying physiological mechanism is largely unknown. In the present study, two maize inbred lines (Ye478 and Wu312) were used to study the possible involvement of the auxin and target of rapamycin (TOR) pathway in low-N-induced root elongation. Compared to Wu312, primary root elongation of Ye478 was more sensitive to low nitrate supply. Correspondingly, more auxin was accumulated in the root tip, and more protons were secreted, increasing the acidity of the apoplast space. On the other hand, low-N-induced root elongation was greatly reduced when shoot-to-root auxin transport was inhibited by applying N-1-naphthylphthalamic acid (NPA) at the plant base or by pruning the top leaf where auxin is mostly synthesized. Furthermore, exogenous application of TOR inhibitor also eliminated the response of root elongation under low N. The content of TOR kinase and the expression of TOR pathway-related genes were significantly changed when shoot-to-root auxin transport was reduced by NPA treatment. Taken together, it is concluded that low-N stress increases shoot-to-root auxin transport which enhances root elongation via auxin-dependent acid growth and the auxin-regulated TOR pathway in maize.

Efficient detection doxorubicin hydrochloride using CuInSe2@ZnS quantum dots and Ag nanoparticles.

Doxorubicin hydrochloride (DOX) is an effective anthracycline anticancer drug. However, the exceeded taken up could induce several side-effects such as cardiotoxicity, alopecia. Therefore, the level of DOX needs to be closely monitored to avoid the occurrence of its side-effects. Herein, we report a novel core CuInSe2 - shell ZnS quantum dots (CuInSe2@ZnS, QDs) and Ag nanoparticles (NPs) fluorescence sensor based on the surface plasmon resonance effect (SPR) of Ag NPs. The CuInSe2@ZnS QDs were prepared by water phase reflux method with the 3-mercaptopropionic acid (MPA) as stabilizer and ligand. The fluorescence intensity of CuInSe2@ZnS QDs/Ag NPs significantly reduced by DOX, which is mainly based on the electrostatic interaction between the DOX and fluorescence sensors. The inhibition of photoluminescence (ln F0/F) was linearly relationship to the concentration of DOX in the range of 2-100 µM with the detection limit as low as 0.05 µM. The as-prepared sensor has a high selectivity and sensitivity to DOX. Furthermore, the new sensor has been successfully applied to the determination of DOX in human serum samples with satisfactory results. Our work provides a clue for developing a novel CuInSe2@ZnS QDs/Ag NPs based fluorescence sensor for DOX detection.

Combined physiological, transcriptome, and genetic analysis reveals a molecular network of nitrogen remobilization in maize.

In plants, nitrogen remobilization from source to sink organs is an important process regulated by complex transcriptional regulatory networks. However, the relationship between nitrogen remobilization and leaf senescence and the molecular regulatory network that controls them are unknown in maize. Here, using 15N labeling and a transcriptome approach, a dynamic analysis of the nitrogen remobilization process was conducted in two elite maize inbred lines (PH4CV and PH6WC) with contrasting leaf senescence. PH4CV showed higher nitrogen remobilization efficiency (NRE) than PH6WC, mainly in the middle and lower leaves from 15 d to 35 d after silking. The co-expression network analysis revealed that ethylene and cytokinin metabolism-related genes triggered the onset of nitrogen remobilization, while abscisic acid and jasmonic acid biosynthesis-related genes controlled the progression of nitrogen remobilization. By integrating genetic analysis, functional annotation, and gene expression, two candidate genes underlying a major quantitative trait locus of NRE were identified, namely an early senescence acting gene (ZmASR6) and an ATP-dependent Clp protease gene (GRMZM2G172230). Hormone-coupled transcription factors and downstream target genes reveal a gene regulatory network for the nitrogen remobilization process after silking in maize. These results uncovered a sophisticated regulatory mechanism for nitrogen remobilization, and further provided characterization of valuable genes for genetic improvement of nitrogen use efficiency in maize.

Involvement of a truncated MADS-box transcription factor ZmTMM1 in root nitrate foraging.

Plants can develop root systems with distinct anatomical features and morphological plasticity to forage nutrients distributed heterogeneously in soils. Lateral root proliferation is a typical nutrient-foraging response to a local supply of nitrate, which has been investigated across many plant species. However, the underlying mechanism in maize roots remains largely unknown. Here, we report on identification of a maize truncated MIKC-type MADS-box transcription factor (ZmTMM1) lacking K- and C-domains, expressed preferentially in the lateral root branching zone and induced by the localized supply of nitrate. ZmTMM1 belongs to the AGL17-like MADS-box transcription factor family that contains orthologs of ANR1, a key regulator for root nitrate foraging in Arabidopsis. Ectopic overexpression of ZmTMM1 recovers the defective growth of lateral roots in the Arabidopsis anr1 agl21 double mutant. The local activation of glucocorticoid receptor fusion proteins for ZmTMM1 and an artificially truncated form of AtANR1 without the K- and C-domains stimulates the lateral root growth of the Arabidopsis anr1 agl21 mutant, providing evidence that ZmTMM1 encodes a functional MADS-box that modulates lateral root development. However, no phenotype was observed in ZmTMM1-RNAi transgenic maize lines, suggesting a possible genetic redundancy of ZmTMM1 with other AGL17-like genes in maize. A comparative genome analysis further suggests that a nitrate-inducible transcriptional regulation is probably conserved in both truncated and non-truncated forms of ZmTMM1-like MADS-box transcription factors found in grass species.

The physiological mechanism underlying root elongation in response to nitrogen deficiency in crop plants.

MAIN CONCLUSION: In response to low nitrogen stress, multiple hormones together with nitric oxide signaling pathways work synergistically and antagonistically in crop root elongation. Changing root morphology allows plants to adapt to soil nutrient availability. Nitrogen is the most important essential nutrient for plant growth. An important adaptive strategy for crops responding to nitrogen deficiency is root elongation, thereby accessing increased soil space and nitrogen resources. Multiple signaling pathways are involved in this regulatory network, working together to fine-tune root elongation in response to soil nitrogen availability. Based on existing research, we propose a model to explain how different signaling pathways interact to regulate root elongation in response to low nitrogen stress. In response to a low shoot nitrogen status signal, auxin transport from the shoot to the root increases. High auxin levels in the root tip stimulate the production of nitric oxide, which promotes the synthesis of strigolactones to accelerate cell division. In this process, cytokinin, ethylene, and abscisic acid play an antagonistic role, while brassinosteroids and auxin play a synergistic role in regulating root elongation. Further study is required to identify the QTLs, genes, and favorable alleles which control the root elongation response to low nitrogen stress in crops.

The Role of Gibberellins in Regulation of Nitrogen Uptake and Physiological Traits in Maize Responding to Nitrogen Availability.

Modified gibberellin (GA) signaling leads to semi-dwarfism with low nitrogen (N) use efficiency (NUE) in crops. An understanding of GA-mediated N uptake is essential for the development of crops with improved NUE. The function of GA in modulating N uptake capacity and nitrate (NO3-) transporters (NRTs) was analyzed in the GA synthesis-deficient mutant zmga3ox grown under low (LN) and sufficient (SN) N conditions. LN significantly suppressed the production of GA1, GA3, and GA4, and the zmga3ox plants showed more sensitivity in shoots as well as LN stress. Moreover, the higher anthocyanin accumulation and the decrease of chlorophyll content were also recorded. The net NO3- fluxes and 15N content were decreased in zmga3ox plants under both LN and SN conditions. Exogenous GA3 could restore the NO3- uptake in zmga3ox plants, but uniconazole repressed NO3- uptake. Moreover, the transcript levels of ZmNRT2.1/2.2 were downregulated in zmga3ox plants, while the GA3 application enhanced the expression level. Furthermore, the RNA-seq analyses identified several transcription factors that are involved in the GA-mediated transcriptional operation of NRTs related genes. These findings revealed that GAs influenced N uptake involved in the transcriptional regulation of NRTs and physiological responses in maize responding to nitrogen supply.