Humic Acid Improves Zn Fertilization in Oxisols Successively Cultivated with Maize-Brachiaria

Zinc (Zn) is an essential micronutrient for plant growth, and Zn deficiency is a global issue, especially in tropical soils. This study aimed to investigate the effects of humic acid (HA) and the Zn addition (Zn sulfate + HA) on the growth of maize and brachiaria in two contrasting Oxisols. The potential complexation of Zn sulfate by HA was evaluated by Fourier-transform infrared (FTIR) spectroscopy analysis. Zinc content and its availability in solution and the shoot and root biomass of maize and brachiaria were determined. FTIR spectroscopy revealed the complexation of Zn sulfate by HA through its S and C functional groups. In both Oxisols, solution Zn increased due to the combined use of Zn and HA. In a soil type-dependent manner, maize biomass and Zn in its shoots were affected only by the exclusive use of Zn fertilization. In the Yellow Oxisol, brachiaria growth and Zn accumulated in its shoot were positively affected by the combined use of Zn fertilization with HA. In the Oxisol with lower organic matter content, HA can assure adequate supplying of residual Zn, while increasing growth of brachiaria cultivated in sequence to maize.

Identification for surrogate drought tolerance in maize inbred lines utilizing high-throughput phenomics approach

Screening for drought tolerance requires precise techniques like phonemics, which is an emerging science aimed at non-destructive methods allowing large-scale screening of genotypes. Large-scale screening complements genomic efforts to identify genes relevant for crop improvement. Thirty maize inbred lines from various sources (exotic and indigenous) maintained at Dryland Agriculture Research Station were used in the current study. In the automated plant transport and imaging systems (LemnaTec Scanalyzer system for large plants), top and side view images were taken of the VIS (visible) and NIR (near infrared) range of the light spectrum to capture phenes. All images were obtained with a thermal imager. All sensors were used to collect images one day after shifting the pots from the greenhouse for 11 days. Image processing was done using pre-processing, segmentation and flowered by features' extraction. Different surrogate traits such as pixel area, plant aspect ratio, convex hull ratio and calliper length were estimated. A strong association was found between canopy temperature and above ground biomass under stress conditions. Promising lines in different surrogates will be utilized in breeding programmes to develop mapping populations for traits of interest related to drought resilience, in terms of improved tissue water status and mapping of genes/QTLs for drought traits.

Physiological Response of Maize Plants (Zea mays L.) to the Use of the Potassium Quercetin Derivative

Plant production technologies based solely on the improvement of plants themselves face obstacles resulting from the natural limitations of the biological potential of varieties. Therefore, new substances are sought that positively influence the growth and development of plants and increase resistance to various biotic and abiotic stresses, which also translates into an increase in obtained yields. The exogenous application of various phytoprotectants shows great promise in terms of cost effectiveness compared to traditional breeding methods or transgenic approaches in relation to increasing plant tolerance to abiotic stresses. Quercetin is a strong antioxidant among phenolic compounds, and it plays a physiological and biochemical role in plants. As such, the aim of this research was to assess the effect of an aqueous solution of a quercetin derivative with potassium, applied in various concentrations (0.5%, 1.0%, 3.0% and 5.0%), on the efficiency of the photosynthetic apparatus and biochemical properties of maize. Among the tested variants, compared to the control, the most stimulating effect on the course of physiological processes (PN, gs, ci, CCI, Fv/Fm, Fv/F0, PI) in maize leaves was found in 3.0 and 5.0% aqueous solutions of the quercetin derivative. The highest total antioxidant capacity and total content of polyphenolic compounds were found for plants sprayed with 5.0% quercetin derivative solution; therefore, in this study, the optimal concentration could not be clearly selected.

Exogenously Applied Gibberellic Acid Enhances Growth and Salinity Stress Tolerance of Maize through Modulating the Morpho-Physiological, Biochemical and Molecular Attributes

Soil salinity is the major limiting factor restricting plant growth and development. Little is known about the comparative and combined effects of gibberellic acid (GA3) seed priming and foliar application on maize under salt stress. The current study determined the impact of different application methods of GA3 on morpho-physiological, biochemical and molecular responses of maize seedlings under three salinity stress treatments (no salinity, moderate salinity-6 dS m-1, and severe salinity-12 dS m-1). The GA3 treatments consisted of control, hydro-priming (HP), water foliar spray (WFS), HP + WFS, seed priming with GA3 (GA3P, 100 mg L-1), foliar spray with GA3 (GA3FS, 100ppm) and GA3P + GA3FS. Salt stress particularly at 12 dS m-1 reduced the length of shoots and roots, fresh and dry weights, chlorophyll, and carotenoid contents, K+ ion accumulation and activities of antioxidant enzymes, while enhanced the oxidative damage and accumulation of the Na+ ion in maize plants. Nevertheless, the application of GA3 improved maize growth, reduced oxidative stress, and increased the antioxidant enzymes activities, antioxidant genes expression, and K+ ion concentration under salt stress. Compared with control, the GA3P + GA3FS recorded the highest increase in roots and shoots length (19-37%), roots fresh and dry weights (31-43%), shoots fresh and dry weights (31-47%), chlorophyll content (21-70%), antioxidant enzymes activities (73.03-150.74%), total soluble protein (13.05%), K+ concentration (13-23%) and antioxidants genes expression levels under different salinity levels. This treatment also reduced the H2O2 content, and Na+ ion concentration. These results indicated that GA3P + GA3FS could be used as an effective tool for improving the maize growth and development, and reducing the oxidative stress in salt-contaminated soils.

Synthesis and regulation of auxin and abscisic acid in maize

Indole-3-acetic acid (IAA), the primary auxin in higher plants, and abscisic acid (ABA) play crucial roles in the ability of maize (Zea mays L.) to acclimatize to various environments by mediating growth, development, defense and nutrient allocation. Although understanding the biochemical reactions for IAA and ABA biosynthesis and signal transduction has progressed, the mechanisms by which auxin and ABA are synthesized and transduced in maize have not been fully elucidated to date. The synthesis and signal transduction pathway of IAA and ABA in maize can be analyzed using an existing model. This article focuses on the research progress toward understanding the synthesis and signaling pathways of IAA and ABA, as well as IAA and ABA regulation of maize growth, providing insight for future development and the significance of IAA and ABA for maize improvement.

A nitrate transporter encoded by ZmNPF7.9 is essential for maize seed development

Nitrogen is an essential macronutrient for plants and regulates many aspects of plant growth and development. Nitrate is one of the major forms of nitrogen in plants. However, the role of nitrate uptake and allocation in seed development is not fully understood. Here, we identified the maize (Zea mays) small-kernel mutant zmnpf7.9 and characterized the candidate gene, ZmNPF7.9, which was the same gene as nitrate transport 1.5 (NRT1.5) in maize. This gene is specifically expressed in the basal endosperm transfer layer cells of maize endosperm. Dysfunction of ZmNPF7.9 resulted in delayed endosperm development, abnormal starch deposition and decreased hundred-grain weight. Functional analysis of cRNA-injected Xenopus oocytes showed that ZmNPF7.9 is a low-affinity, pH-dependent bidirectional nitrate transporter. Moreover, the amount of nitrate in mature seeds of the zmnpf7.9 mutant was reduced. These suggest that ZmNPF7.9 is involved in delivering nitrate from maternal tissues to the developing endosperm. Moreover, most of the key genes associated with glycolysis/gluconeogenesis, carbon fixation, carbon metabolism and biosynthesis of amino acids pathways in the zmnpf7.9 mutant were significantly down-regulated. Thus, our results demonstrate that ZmNPF7.9 plays a specific role in seed development and grain weight by regulating nutrition transport and metabolism, which might provide useful information for maize genetic improvement.

Towards a dynamic photosynthesis model to guide yield improvement in C4 crops

The most productive C4 food and biofuel crops, such as Saccharum officinarum (sugarcane), Sorghum bicolor (sorghum) and Zea mays (maize), all use NADP-ME-type C4 photosynthesis. Despite high productivities, these crops fall well short of the theoretical maximum solar conversion efficiency of 6%. Understanding the basis of these inefficiencies is key for bioengineering and breeding strategies to increase the sustainable productivity of these major C4 crops. Photosynthesis is studied predominantly at steady state in saturating light. In field stands of these crops light is continually changing, and often with rapid fluctuations. Although light may change in a second, the adjustment of photosynthesis may take many minutes, leading to inefficiencies. We measured the rates of CO₂ uptake and stomatal conductance of maize, sorghum and sugarcane under fluctuating light regimes. The gas exchange results were combined with a new dynamic photosynthesis model to infer the limiting factors under non-steady-state conditions. The dynamic photosynthesis model was developed from an existing C4 metabolic model for maize and extended to include: (i) post-translational regulation of key photosynthetic enzymes and their temperature responses; (ii) dynamic stomatal conductance; and (iii) leaf energy balance. Testing the model outputs against measured rates of leaf CO₂ uptake and stomatal conductance in the three C4 crops indicated that Rubisco activase, the pyruvate phosphate dikinase regulatory protein and stomatal conductance are the major limitations to the efficiency of NADP-ME-type C4 photosynthesis during dark-to-high light transitions. We propose that the level of influence of these limiting factors make them targets for bioengineering the improved photosynthetic efficiency of these key crops.

Influence of climate change and mechanized harvesting on maize (Zea mays L.) planting and northern limits in northeast China

BACKGROUND

Northeast China is one of the most important maize producing areas in China. Due to limitations on crop growth resulting from temperature, whether this area can realize mechanical kernel harvesting maize (MKHM) will directly affect the stable development of maize in the region. The effects of climate change on the northern limits of early maturing MKHM were also analyzed in the study.

RESULTS

The mean temperature during the maize growth period increased at a rate of 0.22 °C/10a from 1960 to 2018. The average growth periods for early, middle- and late-maturing common harvest maize (CHM) were 123, 135, and 140 days, respectively, and the accumulated temperature above 10 °C (AAT10) was 2400 °C, 2800 °C, and 3100 °C. The early maturing MKHM growth period was about 20 days longer than that of early maturing CHM, and thus the AAT10 of the MKHM was 2700 °C. From 2000-2018, the northern limits for the early maturing CHM maize planting were located from south of Nenjiang and Wudalianchi (47° 98' N-49° 74' N), while the northern limits for the early maturing MKHM maize were located in south Keshan, Nehe, and Hailun (46° 32' N-48° 70' N), which was about 148 km southward compared to the northern limits of the early maturing CHM maize.

CONCLUSION

This study not only confirmed the northern limits of early maturing MKHM maize but also indicated that the development of MKHM offsets the influences of climate change on the northern limits of maize planting. This is very important for the sustainable development of maize in the region. © 2020 Society of Chemical Industry.

A species-specific functional module controls formation of pollen apertures

Pollen apertures are an interesting model for the formation of specialized plasma-membrane domains. The plant-specific protein INP1 serves as a key aperture factor in such distantly related species as Arabidopsis, rice and maize. Although INP1 orthologues probably play similar roles throughout flowering plants, they show substantial sequence divergence and often cannot substitute for each other, suggesting that INP1 might require species-specific partners. Here, we present a new aperture factor, INP2, which satisfies the criteria for being a species-specific partner for INP1. Both INP proteins display similar structural features, including the plant-specific DOG1 domain, similar patterns of expression and mutant phenotypes, as well as signs of co-evolution. These proteins interact with each other in a species-specific manner and can restore apertures in a heterologous system when both are expressed but not when expressed individually. Our findings suggest that the INP proteins form a species-specific functional module that underlies formation of pollen apertures.

Comparative Transcriptome Analysis Reveals Regulatory Networks during the Maize Ear Shank Elongation Process

In maize, the ear shank is a short branch that connects the ear to the stalk. The length of the ear shank mainly affects the transportation of photosynthetic products to the ear, and also influences the dehydration of the grain by adjusting the tightness of the husks. However, the molecular mechanisms of maize shank elongation have rarely been described. It has been reported that the maize ear shank length is a quantitative trait, but its genetic basis is still unclear. In this study, RNA-seq was performed to explore the transcriptional dynamics and determine the key genes involved in maize shank elongation at four different developmental stages. A total of 8145 differentially expressed genes (DEGs) were identified, including 729 transcription factors (TFs). Some important genes which participate in shank elongation were detected via function annotation and temporal expression pattern analyses, including genes related to signal transduction hormones (auxin, brassinosteroids, gibberellin, etc.), xyloglucan and xyloglucan xyloglucosyl transferase, and transcription factor families. The results provide insights into the genetic architecture of maize ear shanks and developing new varieties with ideal ear shank lengths, enabling adjustments for mechanized harvesting in the future.

Drought affects the rate and duration of organ growth but not inter-organ growth coordination

Drought at flowering and grain filling greatly reduces maize (Zea mays) yield. Climate change is causing earlier and longer-lasting periods of drought, which affect the growth of multiple maize organs throughout development. To study how long periods of water deficit impact the dynamic nature of growth, and to determine how these relate to reproductive drought, we employed a high-throughput phenotyping platform featuring precise irrigation, imaging systems, and image-based biomass estimations. Prolonged drought resulted in a reduction of growth rate of individual organs-though an extension of growth duration partially compensated for this-culminating in lower biomass and delayed flowering. However, long periods of drought did not affect the highly organized succession of maximal growth rates of the distinct organs, i.e. leaves, stems, and ears. Two drought treatments negatively affected distinct seed yield components: Prolonged drought mainly reduced the number of spikelets, and drought during the reproductive period increased the anthesis-silking interval. The identification of these divergent biomass and yield components, which were affected by the shift in duration and intensity of drought, will facilitate trait-specific breeding toward future climate-resilient crops.

Vulnerability of maize, millet, and rice yields to growing season precipitation and socio-economic proxies in Cameroon

In sub-Saharan Africa growing season precipitation is affected by climate change. Due to this, in Cameroon, it is uncertain how some crops are vulnerable to growing season precipitation. Here, an assessment of the vulnerability of maize, millet, and rice to growing season precipitation is carried out at a national scale and validated at four sub-national scales/sites. The data collected were historical yield, precipitation, and adaptive capacity data for the period 1961–2019 for the national scale analysis and 1991–2016 for the sub-national scale analysis. The crop yield data were collected for maize, millet, and rice from FAOSTAT and the global yield gap atlas to assess the sensitivity both nationally and sub-nationally. Historical data on mean crop growing season and mean annul precipitation were collected from a collaborative database of UNDP/Oxford University and the climate portal of the World Bank to assess the exposure both nationally and sub-nationally. To assess adaptive capacity, literacy, and poverty rate proxies for both the national and regional scales were collected from KNOEMA and the African Development Bank. These data were analyzed using a vulnerability index that is based on sensitivity, exposure, and adaptive capacity. The national scale results show that millet has the lowest vulnerability index while rice has the highest. An inverse relationship between vulnerability and adaptive capacity is observed. Rice has the lowest adaptive capacity and the highest vulnerability index. Sub-nationally, this work has shown that northern maize is the most vulnerable crop followed by western highland rice. This work underscores the fact that at different scales, crops are differentially vulnerable due to variations in precipitation, temperature, soils, access to farm inputs, exposure to crop pest and variations in literacy and poverty rates. Therefore, caution should be taken when transitioning from one scale to another to avoid generalization. Despite these differences, in the sub-national scale, western highland rice is observed as the second most vulnerable crop, an observation similar to the national scale observation.

An integrated framework reinstating the environmental dimension for GWAS and genomic selection in crops

Identifying mechanisms and pathways involved in gene-environment interplay and phenotypic plasticity is a long-standing challenge. It is highly desirable to establish an integrated framework with an environmental dimension for complex trait dissection and prediction. A critical step is to identify an environmental index that is both biologically relevant and estimable for new environments. With extensive field-observed complex traits, environmental profiles, and genome-wide single nucleotide polymorphisms for three major crops (maize, wheat, and oat), we demonstrated that identifying such an environmental index (i.e., a combination of environmental parameter and growth window) enables genome-wide association studies and genomic selection of complex traits to be conducted with an explicit environmental dimension. Interestingly, genes identified for two reaction-norm parameters (i.e., intercept and slope) derived from flowering time values along the environmental index were less colocalized for a diverse maize panel than for wheat and oat breeding panels, agreeing with the different diversity levels and genetic constitutions of the panels. In addition, we showcased the usefulness of this framework for systematically forecasting the performance of diverse germplasm panels in new environments. This general framework and the companion CERIS-JGRA analytical package should facilitate biologically informed dissection of complex traits, enhanced performance prediction in breeding for future climates, and coordinated efforts to enrich our understanding of mechanisms underlying phenotypic variation.

Low nitrogen availability inhibits the phosphorus starvation response in maize (Zea mays ssp. mays L.)

BACKGROUND

Nitrogen (N) and phosphorus (P) are macronutrients essential for crop growth and productivity. In cultivated fields, N and P levels are rarely sufficient, contributing to the gap between realized and potential production. Fertilizer application increases nutrient availability, but is not available to all farmers, nor are current rates of application sustainable or environmentally desirable. Transcriptomic studies of cereal crops have revealed dramatic responses to either low N or low P single stress treatments. In the field, however, levels of both N and P may be suboptimal. The interaction between N and P starvation responses remains to be fully characterized.

RESULTS

We characterized growth and root and leaf transcriptomes of young maize plants under nutrient replete, low N, low P or combined low NP conditions. We identified 1555 genes to respond to our nutrient treatments, in one or both tissues. A large group of genes, including many classical P starvation response genes, were regulated antagonistically between low N and P conditions. An additional experiment over a range of N availability indicated that a mild reduction in N levels was sufficient to repress the low P induction of P starvation genes. Although expression of P transporter genes was repressed under low N or low NP, we confirmed earlier reports of P hyper accumulation under N limitation.

CONCLUSIONS

Transcriptional responses to low N or P were distinct, with few genes responding in a similar way to the two single stress treatments. In combined NP stress, the low N response dominated, and the P starvation response was largely suppressed. A mild reduction in N availability was sufficient to repress the induction of P starvation associated genes. We conclude that activation of the transcriptional response to P starvation in maize is contingent on N availability.

The diverse functional genes of maize rhizosphere microbiota assessed using shotgun metagenomics

BACKGROUND

The geographical diversification in chemical, biological and physical properties of plant biospheres instigates heterogenicity in the proliferation of important soil microbiome. Controlling functions and structure of plant rhizosphere from a better understanding and prediction of a plant's immediate environment will help assess plant-microbe interplay, improve the productivity of plant ecosystems and improve plant response to adverse soil conditions. Here we characterized functional genes of the microbial community of maize rhizosphere using a culture-independent method.

RESULTS

Our metadata showed microbial genes involved in nitrogen fixation, phosphate solubilization, quorum sensing molecules, trehalose, siderophore production, phenazine biosynthesis protein, daunorubicin resistance, acetoin, 1-aminocyclopropane-1-carboxylate deaminase, 4-hydroxybenzoate, disease control and stress-reducing genes (superoxidase dismutase, catalase, peroxidase, etc.). β-Diversity showed that there is a highly significant difference between most of the genes mined from rhizosphere soil samples and surrounding soils.

CONCLUSIONS

The high relative abundance of stress-reducing genes mined from this study showed that the sampling sites harbor not only important plant-beneficial organisms but also a hotspot for developing bio-fertilizers. Nevertheless, since most of these organisms are unculturable, mapping cultivation strategies for their growth could make them readily available as bio-inoculants and possible biotechnological applications in the future. © 2020 Society of Chemical Industry.

Elucidating compositional factors of maize cell walls contributing to stalk strength and lodging resistance

Lodging is one of the causes of maize (Zea mays L.) production losses worldwide and, at least, the resistance to stalk lodging has been positively correlated with stalk strength. In order to elucidate the putative relationship between cell wall, stalk strength and lodging resistance, twelve maize inbreds varying in rind penetration strength and lodging resistance were characterized for cell wall composition and structure. Stepwise multiple regression indicates that H lignin subunits confer a greater rind penetration strength. Besides, the predictive model for lodging showed that a high ferulic acid content increases the resistance to lodging, whereas those of diferulates decrease it. These outcomes highlight that the strength and lodging susceptibility of maize stems may be conditioned by structural features of cell wall rather than by the net amount of cellulose, hemicelluloses and lignin. The results presented here provide biotechnological targets in breeding programs aimed at improving lodging in maize.

Effects and Economic Sustainability of Biochar Application on Corn Production in a Mediterranean Climate

The effects of two types of biochar on corn production in the Mediterranean climate during the growing season were analyzed. The two types of biochar were obtained from pyrolysis of Pinus pinaster. B1 was fully pyrolyzed with 55.90% organic carbon, and B2 was medium pyrolyzed with 23.50% organic carbon. B1 and B2 were supplemented in the soil of 20 plots (1 m2) at a dose of 4 kg/m2. C1 and C2 (10 plots each) served as control plots. The plots were automatically irrigated and fertilizer was not applied. The B1-supplemented plots exhibited a significant 84.58% increase in dry corn production per square meter and a 93.16% increase in corn wet weight (p << 0.001). Corn production was no different between B2-supplemented, C1, and C2 plots (p > 0.01). The weight of cobs from B1-supplemented plots was 62.3%, which was significantly higher than that of cobs from C1 and C2 plots (p < 0.01). The grain weight increased significantly by 23% in B1-supplemented plots (p < 0.01) and there were no differences between B2-supplemented, C1, and C2 plots. At the end of the treatment, the soil of the B1-supplemented plots exhibited increased levels of sulfate, nitrate, magnesium, conductivity, and saturation percentage. Based on these results, the economic sustainability of this application in agriculture was studied at a standard price of €190 per ton of biochar. Amortization of this investment can be achieved in 5.52 years according to this cost. Considering the fertilizer cost savings of 50% and the water cost savings of 25%, the amortization can be achieved in 4.15 years. If the price of biochar could be reduced through the CO2 emission market at €30 per ton of non-emitted CO2, the amortization can be achieved in 2.80 years. Biochar markedly improves corn production in the Mediterranean climate. However, the amortization time must be further reduced, and enhanced production must be guaranteed over the years with long term field trials so that the product is marketable or other high value-added crops must be identified.

Sulfur transfer from the endophytic fungus Serendipita indica improves maize growth and requires the sulfate transporter SiSulT

A deficiency of the essential macronutrient sulfur leads to stunted plant growth and yield loss; however, an association with a symbiotic fungus can greatly improve nutrient uptake by the host plant. Here, we identified and functionally characterized a high-affinity sulfate transporter from the endophytic fungus Serendipita indica. SiSulT fulfills all the criteria expected of a functional sulfate transporter responding to sulfur limitation: SiSulT expression was induced when S. indica was grown under low-sulfate conditions, and heterologous expression of SiSulT complemented a yeast mutant lacking sulfate transport. We generated a knockdown strain of SiSulT by RNA interference to investigate the consequences of the partial loss of this transporter for the fungus and the host plant (maize, Zea mays) during colonization. Wild-type (WT) S. indica, but not the knockdown strain (kd-SiSulT), largely compensated for low-sulfate availability and supported plant growth. Colonization by WT S. indica also allowed maize roots to allocate precious resources away from sulfate assimilation under low-sulfur conditions, as evidenced by the reduction in expression of most sulfate assimilation genes. Our study illustrates the utility of the endophyte S. indica in sulfur nutrition research and offers potential avenues for agronomically sound amelioration of plant growth in low-sulfate environments.

Alternative Strategies for Multi-Stress Tolerance and Yield Improvement in Millets

Millets are important cereal crops cultivated in arid and semiarid regions of the world, particularly Africa and southeast Asia. Climate change has triggered multiple abiotic stresses in plants that are the main causes of crop loss worldwide, reducing average yield for most crops by more than 50%. Although millets are tolerant to most abiotic stresses including drought and high temperatures, further improvement is needed to make them more resilient to unprecedented effects of climate change and associated environmental stresses. Incorporation of stress tolerance traits in millets will improve their productivity in marginal environments and will help in overcoming future food shortage due to climate change. Recently, approaches such as application of plant growth-promoting rhizobacteria (PGPRs) have been used to improve growth and development, as well as stress tolerance of crops. Moreover, with the advance of next-generation sequencing technology, genome editing, using the clustered regularly interspaced short palindromic repeats (CRISPR/Cas9) system are increasingly used to develop stress tolerant varieties in different crops. In this paper, the innate ability of millets to tolerate abiotic stresses and alternative approaches to boost stress resistance were thoroughly reviewed. Moreover, several stress-resistant genes were identified in related monocots such as rice (Oryza sativa), wheat (Triticum aestivum), and maize (Zea mays), and other related species for which orthologs in millets could be manipulated by CRISPR/Cas9 and related genome-editing techniques to improve stress resilience and productivity. These cutting-edge alternative strategies are expected to bring this group of orphan crops at the forefront of scientific research for their potential contribution to global food security.

A Fructan Exohydrolase from Maize Degrades Both Inulin and Levan and Co-Exists with 1-Kestotriose in Maize

Enzymes with fructan exohydrolase (FEH) activity are present not only in fructan-synthesizing species but also in non-fructan plants. This has led to speculation about their functions in non-fructan species. Here, a cell wall invertase-related Zm-6&1-FEH2 with no "classical" invertase motif was identified in maize. Following heterologous expression in Pichia pastoris and in Nicotiana benthamiana leaves, the enzyme activity of recombinant Zm-6&1-FEH2 displays substrate specificity with respect to inulin and levan. Subcellular localization showed Zm-6&1-FEH2 exclusively localized in the apoplast, and its expression profile was strongly dependent on plant development and in response to drought and abscisic acid. Furthermore, formation of 1-kestotriose, an oligofructan, was detected in vivo and in vitro and could be hydrolyzed by Zm-6&1-FEH2. In summary, these results support that Zm-6&1-FEH2 enzyme from maize can degrade both inulin-type and levan-type fructans, and the implications of the co-existence of Zm-6&1-FEH2 and 1-kestotriose are discussed.

Environmental and economic concerns surrounding restrictions on glyphosate use in corn

Since the commercialization of transgenic glyphosate-tolerant (GT) crops in the mid-1990s, glyphosate has become the dominant herbicide to control weeds in corn, soybean, and other crops in the United States and elsewhere. However, recent public concerns over its potential carcinogenicity in humans have generated calls for glyphosate-restricting policies. Should a policy to restrict glyphosate use, such as a glyphosate tax, be implemented? The decision involves two types of tradeoffs: human health and environmental (HH-E) impacts versus market economic impacts, and the use of glyphosate versus alternative herbicides, where the alternatives potentially have more serious adverse HH-E effects. Accounting for farmers' weed management choices, we provide empirical evaluation of the HH-E welfare and market economic welfare effects of a glyphosate use restriction policy on US corn production. Under a glyphosate tax, farmers would substitute glyphosate for a combination of other herbicides. Should a 10% glyphosate tax be imposed, then the most conservative welfare estimate is a net HH-E welfare gain with a monetized value of US$6 million per annum but also a net market economic loss of US$98 million per annum in the United States, which translates into a net loss in social welfare. This result of overall welfare loss is robust to a wide range of tax rates considered, from 10 to 50%, and to multiple scenarios of glyphosate's HH-E effects, which are the primary sources of uncertainties about glyphosate's effects.

Major locus for spontaneous haploid genome doubling detected by a case-control GWAS in exotic maize germplasm

A major locus for spontaneous haploid genome doubling was detected by a case-control GWAS in an exotic maize germplasm. The combination of double haploid breeding method with this locus leads to segregation distortion on genomic regions of chromosome five. Temperate maize (Zea mays L.) breeding programs often rely on limited genetic diversity, which can be expanded by incorporating exotic germplasm. The aims of this study were to perform characterization of inbred lines derived from the tropical BS39 population using different breeding methods, to identify genomic regions showing segregation distortion in lines derived by the DH process using spontaneous haploid genome doubling (SHGD), and use case-control association mapping to identify loci controlling SHGD. Four different sets were used: BS39_DH and BS39_SSD were derived from the BS39 population by DH and single-seed descendent (SSD) methods, and BS39 × A427_DH and BS39 × A427_SSD from the cross between BS39 and A427. A total of 663 inbred lines were genotyped. The analyses of gene diversity and genetic differentiation for the DH sets provided evidence of the presence of a SHGD locus near the centromere of chromosome 5. The case-control GWAS for the DH set also pinpointed this locus. Haplotype sharing analysis showed almost 100% exclusive contribution of the A427 genome in the same region on chromosome 5 of BS39 × A427_DH, presumably due to an allele in this region affecting SHGD. This locus enables DH line production in exotic populations without colchicine or other artificial haploid genome doubling.

Optimum Olsen Phosphorus/ZincDTPA ratio for the initial growth of maize in agricultural soils of the Mediterranean region

BACKGROUND

Zinc (Zn) deficiency in crops is commonly aggravated by high levels of phosphorus (P) in soil. In this work, the initial performance of pot-growing maize in response to the available P and Zn in soils with low available Zn and to the application of P and Zn fertilizers was investigated.

RESULTS

The soils (six non-calcareous and 14 calcareous) ranged widely in available P (Olsen P: 5.5-37.9 mg kg^-1 ), were poor in available Zn [diethylenetriaminepentaacetic acid-extractable Zn (Zn_DTPA ): 0.20-0.84 mg kg^-1 ] and had an Olsen P/Zn_DTPA ratio of 13 to 111 mg mg^-1 . Soil P application generally increased aerial dry matter (ADM) yield; Zn increased ADM yield mostly when applied in combination with P; and the sole application of Zn increased yield only in a soil with a high (28 mg kg^-1 ) Olsen P and a low (0.36 mg kg^-1 ) Zn_DTPA . The increase in ADM yield resulting from optimal application of P and/or Zn to the soil was modest in soils where the Olsen P/Zn_DTPA ratio was 30-60 and Olsen P was >14 mg kg^-1 . Zinc uptake by the control plants was correlated with the Zn_DTPA of the soil. For a certain Zn_DTPA value, the level of plant available Zn was higher in non-calcareous than in calcareous soils.

CONCLUSION

Soil application of fertilizer P and Zn, in soils with low levels of available Zn, should not only aim at increasing the available P and Zn levels but also balancing them at the appropriate Olsen P/Zn_DTPA ratio, which was found to lie in the 30-60 range in the present study. © 2020 Society of Chemical Industry.

H2O2 priming induces proteomic responses to defense against salt stress in maize

KEY MESSAGE

H₂O₂ priming reprograms essential proteins' expression to help plants survive, promoting responsive and unresponsive proteins adjustment to salt stress.

ABSTACRT

Priming is a powerful strategy to enhance abiotic stress tolerance in plants. Despite this, there is scarce information about the mechanisms induced by H₂O₂ priming for salt stress tolerance, particularly on proteome modulation. Improving maize cultivation in areas subjected to salinity is imperative for the local economy and food security. Thereby, this study aimed to investigate physiological changes linked with post-translational protein events induced by foliar H₂O₂ priming of Zea mays plants under salt stress. As expected, salt treatment promoted a considerable accumulation of Na⁺ ions, a 12-fold increase. It drastically affected growth parameters and relative water content, as well as promoted adverse alteration in the proteome profile, when compared to the absence of salt conditions. Conversely, H₂O₂ priming was beneficial via specific proteome reprogramming, which promoted better response to salinity by 16% reduction in Na⁺ content and shoots growth improvement, increasing 61% in dry mass. The identified proteins were associated with photosynthesis and redox homeostasis, critical metabolic pathways for helping plants survive in saline stress by the protection of chloroplasts organization and carbon fixation, as well as state redox. This research provides new proteomic data to improve understanding and forward identifying biotechnological strategies to promote salt stress tolerance.

Transcriptome dynamic landscape underlying the improvement of maize lodging resistance under coronatine treatment

BACKGROUND

Lodging is one of the important factors causing maize yield. Plant height is an important factor in determining plant architecture in maize (Zea mays L.), which is closely related to lodging resistance under high planting density. Coronatine (COR), which is a phytotoxin and produced by the pathogen Pseudomonas syringae, is a functional and structural analogue of jasmonic acid (JA).

RESULTS

In this study, we found COR, as a new plant growth regulator, could effectively reduce plant height and ear height of both hybrids (ZD958 and XY335) and inbred (B73) maize by inhibiting internode growth during elongation, thus improve maize lodging resistance. To study gene expression changes in internode after COR treatment, we collected spatio-temporal transcriptome of inbred B73 internode under normal condition and COR treatment, including the three different regions of internode (fixed, meristem and elongation regions) at three different developmental stages. The gene expression levels of the three regions at normal condition were described and then compared with that upon COR treatment. In total, 8605 COR-responsive genes (COR-RGs) were found, consist of 802 genes specifically expressed in internode. For these COR-RGs, 614, 870, 2123 of which showed expression changes in only fixed, meristem and elongation region, respectively. Both the number and function were significantly changed for COR-RGs identified in different regions, indicating genes with different functions were regulated at the three regions. Besides, we found more than 80% genes of gibberellin and jasmonic acid were changed under COR treatment.

CONCLUSIONS

These data provide a gene expression profiling in different regions of internode development and molecular mechanism of COR affecting internode elongation. A putative schematic of the internode response to COR treatment is proposed which shows the basic process of COR affecting internode elongation. This research provides a useful resource for studying maize internode development and improves our understanding of the COR regulation mechanism based on plant height.

Optimizing the P balance: How do modern maize hybrids react to different starter fertilizers?

Phosphorus (P) is an essential macronutrient for plants, but also a limited resource worldwide. Strict regulations for fertilizer applications in the European Union are a consequence of the negative environmental effects in case of improper use. Maize is typically grown with the application of P starter fertilizer, which, however, might be reduced or even omitted if suitable varieties were available. This study was performed with the 20 commercially most important maize hybrids in Germany evaluated in multi-location field trials with the aim to investigate the potential to breed for high-performing maize hybrids under reduced P starter fertilizer. At the core location, three starter fertilizers with either phosphate (triple superphosphate, TSP), ammonium nitrate (calcium ammonium nitrate, CAN), or a combination of ammonium and phosphate (diammonium phosphate, DAP) were evaluated relative to a control and traits from youth development to grain yield were assessed. Significant differences were mainly observed for the DAP starter fertilizer, which was also reflected in a yield increase of on average +0.67 t/ha (+5.34%) compared to the control. Correlations among the investigated traits varied with starter fertilizer, but the general trends remained. As expected, grain yield was negatively correlated with grain P concentration, likely due to a dilution effect. Importantly, the genotype-by-starter fertilizer interaction was always non-significant in the multi-location analysis. This indicates that best performing genotypes can be identified irrespective of the starter fertilizer. Taken together, our results provide valuable insights regarding the potential to reduce starter fertilizers in maize cultivation as well as for breeding maize for P efficiency under well-supplied conditions.

Elucidating the effect of biofertilizers on bacterial diversity in maize rhizosphere soil

This study was conducted to investigate the effect of biofertilizers on the structure and diversity of the rhizosphere bacterial community of maize. Different biofertilizers were applied to maize. The physical and chemical properties of rhizosphere soil samples were analyzed and the rhizosphere bacteria were analyzed by 16S amplicon sequencing. The results showed that treatment with Bacillus licheniformis and B. amyloliquefaciens as biofertilizers increased the soil organic matter (SOM), total nitrogen, total phosphorus (TP), available phosphorus (AP), and available potassium (AK) contents, indicating that the plant growth-promoting rhizobacteria in the biofertilizers might help the host plant to produce root exudates that, in return, recruit beneficial communities due to available sugars, amino acids, organic acids, vitamins, and polymers. The rhizosphere of maize treated with B. subtilis biofertilizer had the highest diversity and richness. However, the rhizosphere treated with the combined bacterial strains had the lowest diversity and richness, which might be due to the directional increase of the abundance of some bacteria with special functions, but the decrease of the overall bacterial community diversity in the soil. The dominant bacterial phyla were Proteobacteria (32.2%–34.6%), Acidobacteria (15.0%–21.0%), Actinobacteria (13.1%–17.2%), and Gemmatimonadetes (9.0%–10.8%), and the dominant bacterial species were Aciditerrimonas ferrireducens JCM 15389 (4.3%–5.2%), Gemmatimonas aurantiaca (3.2%–4.1%), and Pyrinomonas methylaliphatogenes (2.1%–4.8%). The significantly enriched bacterial functions were associated with amino acid metabolism, sugar metabolism, and energy metabolism pathways. The results of a redundancy analysis showed that SOM, TP, and AK were the main factors affecting the microbial community structure in the maize rhizosphere. In conclusion, the application of biofertilizers increased the diversity and richness of the bacterial community in the maize rhizosphere soil. However, combined strain treatment was failed and not an ideal strategy due to the lowest abundance and diversity.

Plant intraspecific competition and growth stage alter carbon and nitrogen mineralization in the rhizosphere

Plant roots interact with rhizosphere microorganisms to accelerate soil organic matter (SOM) mineralization for nutrient acquisition. Root-mediated changes in SOM mineralization largely depend on root-derived carbon (root-C) input and soil nutrient status. Hence, intraspecific competition over plant development and spatiotemporal variability in the root-C input and nutrients uptake may modify SOM mineralization. To investigate the effect of intraspecific competition on SOM mineralization at three growth stages (heading, flowering, and ripening), we grew maize (C4 plant) under three planting densities on a C3 soil and determined in situ soil C- and N-mineralization by ¹³ C-natural abundance and ¹⁵ N-pool dilution approaches. From heading to ripening, soil C- and N-mineralization rates exhibit similar unimodal trends and were tightly coupled. The C-to-N-mineralization ratio (0.6 to 2.6) increased with N availability, indicating that an increase in N-mineralization with N depletion was driven by microorganisms mining N-rich SOM. With the intraspecific competition, plants increased specific root lengths as an efficient strategy to compete for resources. Root morphologic traits rather than root biomass per se were positively related to C- and N-mineralization. Overall, plant phenology and intraspecific competition controlled the intensity and mechanisms of soil C- and N- mineralization by the adaptation of root traits and nutrient mining.

Arbuscular mycorrhizal fungi alter microbiome structure of rhizosphere soil to enhance maize tolerance to La

Rhizosphere microbes are essential partners for plant stress tolerance. Recent studies indicate that arbuscular mycorrhizal fungi (AMF) can facilitate the revegetation of soils contaminated by heavy metals though interacting with rhizosphere microbiome. However, it is unclear how AMF affect rhizosphere microbiome to improve the growth of plant under rare earth elements (REEs) stress. AMF (Claroideoglomus etunicatum) was inoculated to maize grown in soils spiked with Lanthanum (0 mg kg^-1, La0; 10 mg kg^-1, La10; 100 mg kg^-1, La100; 500 mg kg^-1, La500). Plant biomass, nutrient uptake, REE uptake and rhizosphere bacterial and fungal community were evaluated. The results indicated that La100 and La500 decreased significantly root colonization rates and nutrition uptake (K, P, Ca and Mg content). La500 decreased significantly α-diversity indexes of bacterial and fungal community. AMF enhanced significantly the shoot and root fresh and dry weight of maize in all La treatments (except for the root fresh and dry weight of La0 and La10 treatment). For La100 and La500 treatments, AMF increased significantly nutrition uptake (K, P, Ca and Mg content) in shoot of maize by 27.40-441.77%. For La500 treatment, AMF decreased significantly shoot La concentration by 51.53% in maize, but increased significantly root La concentration by 30.45%. In addition, AMF decreased bacterial and fungal Shannon index in La0 treatment, but increased bacterial Shannon index in La500 treatment. Both AMF and La500 affected significantly the bacterial and fungal community composition, and AMF led to more influence than La. AMF promoted the enrichment of bacteria, including Planomicrobium, Lysobacter, Saccharothrix, Agrococcus, Microbacterium, Streptomyces, Penicillium and other unclassified genus, and fungi (Penicillium) in La500, which showed the function for promoting plant growth and tolerance of heavy metal. The study revealed that AMF can regulate the rhizosphere bacterial and fungal composition and foster certain beneficial microbes to enhance the tolerance of maize under La stress. Phytoremediation assisted by AMF is an attractive approach to ameliorate REEs-contaminated soils.

Fine mapping of a kernel length-related gene with potential value for maize breeding

A key candidate gene for maize kernel length was fine mapped to an interval of 942 kb; the locus significantly increases kernel length (KL) and hundred-kernel weight (HKW). Kernel size is a major determinant of yield in cereals. Kernel length, one of the determining factors of kernel size, is a target trait for both domestication and artificial breeding. However, there are few reports of fine mapping and quantitative trait loci (QTLs)/cloned genes for kernel length in maize. In this project, a novel major QTL, named qKL9, controlling maize kernel length was identified. We verified the authenticity and stability of qKL9 via BC₂F₂ and BC₃F₁ populations, respectively, and ultimately mapped qKL9 to an ~ 942-kb genomic interval by testing the progenies of recombination events derived from BC₃F₂ and BC₄F₂ populations in multiple environments. Additionally, one new line (Mc^qKL9-A) containing the ~ 942-kb segment was screened from the BC₄F₂ population. Combining transcriptome analysis between Mc^qKL9-A and Mc at 6, 9 and 14 days after pollination and candidate regional association mapping, Zm00001d046723 was preliminarily identified as the key candidate gene for qKL9. Importantly, the replacement in the Mc line of the Mc's alleles by the V671's alleles in the qKL9 region improved the performances of single-cross hybrids obtained with elite lines, illustrating the potential value of this QTL for the genetic improvement in maize kernel-related traits. These findings facilitate molecular breeding for kernel size and cloning of the gene underlying qKL9, shedding light on the genetic basis of kernel size in maize.

Plant flavones enrich rhizosphere Oxalobacteraceae to improve maize performance under nitrogen deprivation

Beneficial interactions between plant roots and rhizosphere microorganisms are pivotal for plant fitness. Nevertheless, the molecular mechanisms controlling the feedback between root architecture and microbial community structure remain elusive in maize. Here, we demonstrate that transcriptomic gradients along the longitudinal root axis associate with specific shifts in rhizosphere microbial diversity. Moreover, we have established that root-derived flavones predominantly promote the enrichment of bacteria of the taxa Oxalobacteraceae in the rhizosphere, which in turn promote maize growth and nitrogen acquisition. Genetic experiments demonstrate that LRT1-mediated lateral root development coordinates the interactions of the root system with flavone-dependent Oxalobacteraceae under nitrogen deprivation. In summary, these experiments reveal the genetic basis of the reciprocal interactions between root architecture and the composition and diversity of specific microbial taxa in the rhizosphere resulting in improved plant performance. These findings may open new avenues towards the breeding of high-yielding and nutrient-efficient crops by exploiting their interaction with beneficial soil microorganisms.

Can drip irrigation under mulch be replaced with shallow-buried drip irrigation in spring maize production systems in semiarid areas of northern China?

BACKGROUND

In recent years, shallow-buried drip irrigation in spring maize production has gradually replaced drip irrigation under plastic films and has become a common irrigation method in semiarid areas of northern China.

RESULT

Two years of field experiments were carried out in the semiarid area of western Jilin province to compare the two drip irrigation methods in the spring maize production system. The treatments included MW1 (drip irrigation under mulch + moderate irrigation amount), MW2 (drip irrigation under mulch + high irrigation amount), SM1 (shallow-buried drip irrigation + moderate irrigation amount), and SM2 (shallow-buried drip irrigation + high irrigation amount). The maize yields were significantly higher under mulch than under shallow-buried drip irrigation, but there was no interaction between mulch and the irrigation amount. Drip irrigation under mulch greatly improved spring maize N, P and K uptake compared with that under shallow-buried drip irrigation. The agronomic-use efficiency, recovery-use efficiency, and partial factor productivity were ranked in the order of MW2 > MW1 > SW2 > SW1. The water-use efficiency of drip irrigation under mulch was 7.44% and 6.82% higher than that of shallow-buried drip irrigation under the moderate and high irrigation levels, respectively. However, considering the costs of the plastic mulch, there was no significant (P < 0.05) difference in economic benefits between the SW and MW treatments.

CONCLUSION

Drip irrigation under plastic film provides greater advantages for production, but shallow-buried drip irrigation may be a suitable method for farmers until fertigation technology is further optimized and the problem of plastic film pollution is solved. © 2020 Society of Chemical Industry.

Molecular Insights into Inflorescence Meristem Specification for Yield Potential in Cereal Crops

Flowering plants develop new organs throughout their life cycle. The vegetative shoot apical meristem (SAM) generates leaf whorls, branches and stems, whereas the reproductive SAM, called the inflorescence meristem (IM), forms florets arranged on a stem or an axis. In cereal crops, the inflorescence producing grains from fertilized florets makes the major yield contribution, which is determined by the numbers and structures of branches, spikelets and florets within the inflorescence. The developmental progression largely depends on the activity of IM. The proper regulations of IM size, specification and termination are outcomes of complex interactions between promoting and restricting factors/signals. Here, we focus on recent advances in molecular mechanisms underlying potential pathways of IM identification, maintenance and differentiation in cereal crops, including rice (Oryza sativa), maize (Zea mays), wheat (Triticum aestivum), and barley (Hordeum vulgare), highlighting the researches that have facilitated grain yield by, for example, modifying the number of inflorescence branches. Combinatorial functions of key regulators and crosstalk in IM determinacy and specification are summarized. This review delivers the knowledge to crop breeding applications aiming to the improvements in yield performance and productivity.

Water and heat stresses during grain formation affect the physicochemical properties of waxy maize starch

BACKGROUND

Maize is frequently subjected to simultaneous water (drought or waterlogging) and heat (HS) stresses during grain formation in southern China. This work examined the effect of high temperature combined with drought (HD) or waterlogging (HW) during grain formation on the starch physicochemical properties of two waxy maize hybrids, namely Suyunnuo5 (SYN5) and Yunuo7 (YN7).

RESULTS

Heat stress enlarged the starch granule size, and water stresses aggravated this effect. Heat stress reduced the ratio of small molecular weight fractions for both hybrids, and HD aggravated this reduction only in SYN5. Relative crystallinity in SYN5 was increased by stresses but in YN7 it was unaffected by HD, reduced by HS, and increased by HW. Fourier-transform infrared (FTIR) spectrometry results showed that the 1045/1022 cm^-1 ratio in SYN5 was not influenced by HW but was increased by other stresses, and that in YN7 it was increased by all stresses, with the highest value induced by HW. Peak viscosity was decreased, whereas gelatinization temperatures and retrogradation percentage were increased by all of these stresses. These effects were exacerbated by combined heat and water stresses. The maximum decomposition rate was severely increased by HW.

CONCLUSION

Drought or waterlogging at grain formation stage aggravated the detrimental effects of HS on the starch physicochemical properties of waxy maize. © 2020 Society of Chemical Industry.

Elucidating the morpho-physiological adaptations and molecular responses under long-term waterlogging stress in maize through gene expression analysis

Waterlogging stress in maize is one of the emerging abiotic stresses in the current climate change scenario. To gain insights in transcriptional reprogramming during late hours of waterlogging stress under field conditions, we aimed to elucidate the transcriptional and anatomical changes in two contrasting maize inbreds viz. I110 (susceptible) and I172 (tolerant). Waterlogging stress reduced dry matter translocations from leaves and stems to ears, resulting in a lack of sink capacity and inadequate grain filling in I110, thus decreased the grain yield drastically. The development of aerenchyma cells within 48 h in I172 enabled hypoxia tolerance. The upregulation of alanine aminotransferase, ubiquitin activating enzyme E1, putative mitogen activated protein kinase and pyruvate kinase in I172 suggested that genes involved in protein degradation, signal transduction and carbon metabolism provided adaptive mechanisms during waterlogging. Overexpression of alcohol dehydrogenase, sucrose synthase, aspartate aminotransferase, NADP dependent malic enzyme and many miRNA targets in I110 indicated that more oxygen and energy consumption might have shortened plant survival during long-term waterlogging exposure. To the best of our knowledge, this is the first report of transcript profiling at late stage (24-96 h) of waterlogging stress under field conditions and provides new visions to understand the molecular basis of waterlogging tolerance in maize.

Enhancing grain-yield-related traits by CRISPR-Cas9 promoter editing of maize CLE genes

Several yield-related traits selected during crop domestication and improvement^1,2 are associated with increases in meristem size³, which is controlled by CLE peptide signals in the CLAVATA-WUSCHEL pathway^4-13. Here, we engineered quantitative variation for yield-related traits in maize by making weak promoter alleles of CLE genes, and a null allele of a newly identified partially redundant compensating CLE gene, using CRISPR-Cas9 genome editing. These strategies increased multiple maize grain-yield-related traits, supporting the enormous potential for genomic editing in crop enhancement.

Improved photosynthetic characteristics correlated with enhanced biomass in a heterotic F1 hybrid of maize (Zea mays L.)

Heterosis is a phenomenon wherein F₁ hybrid often displays phenotypic superiority and surpasses its parents in terms of growth and agronomic traits. Investigations on the physiological and biochemical properties of the heterotic F₁ hybrid are important to uncover the mechanisms underlying heterosis in plants. In the present study, the photosynthetic capacity of a heterotic F₁ hybrid of Zea mays L. (DHM 117) that exhibited a higher growth rate and increased biomass was compared with its parental inbreds at vegetative and reproductive stages in the field during 2017 and 2018. The net photosynthetic rate (P_n), stomatal conductance (g_s), transpiration rate (E) as well as foliar carbohydrates were higher in F₁ hybrid than parental inbreds at vegetative and reproductive stages. An increase in total chlorophyll content along with better chlorophyll a fluorescence characteristics including effective quantum yield of photosystem II (ΔF/F_m'), maximum quantum yield of PSII (F_v/F_m), photochemical quenching (q_p) and decreased non-photochemical quenching (NPQ) was observed in F₁ hybrid than the parental inbreds. Further, the expression of potential genes related to C₄ photosynthesis was considerably upregulated in F₁ hybrid than the parental inbreds during vegetative and reproductive stages. Moreover, the F₁ hybrid exhibited distinct heterosis in yield with 63% and 62% increase relative to parental inbreds during 2017 and 2018. We conclude that improved photosynthetic efficiency associated with increased foliar carbohydrates could have contributed to higher growth rate, biomass and yield in the F₁ hybrid.

Flowering time regulation model revisited by pooled sequencing of mass selection populations

Maize is one of the most broadly cultivated crops throughout the world, and flowering time is a major adaptive trait for its diffusion. The biggest challenge in understanding maize flowering genetic architecture is that the trait is confounded with population structure. To eliminate the effect, we revisited the flower time genetic network by using a tropical maize population Pop32, which was under mass selection for adaptation to early flowering time in China for six generations from tropical to temperate regions. The days to anthesis (DTA) of the initial (Pop32C0), intermedia (Pop32C3), and final population (Pop32C5) was 90.77, 84.63, and 79.72 days on average, respectively. To examine the genetic mechanism and identify the genetic loci underlying this rapid change in flowering time of Pop32, we bulked 30 individuals from C0, C3, and C5 to conduct the whole genome sequencing. And we finally identified 4,973,810 high-quality single nucleotide polymorphisms (SNPs) and 6,517 genes with allele frequency significantly changed during the artificial improvement process. We speculate that these genes might participate in the adaptive improvement process and control flowering time. To identify the candidate genes for flowering time from the gene set with allele frequency changed, we carried out weighted gene co-expression network analysis (WGCNA), and identified four co-expression modules that highly associated with the flowering time development, as well as constructed the co-expression network of key flowering time genes. Gene Ontology (GO) enrichment analysis revealed that the GO terms photosynthesis/light reaction, carbohydrate binding, auxin mediated signaling pathway, response to temperature stimulus that are closely connected with flowering time. Furthermore, targeted GWAS revealed the genes are significantly connected with the flowering time. qRT-PCR of four candidate genes GRMZM2G019879, GRMZM2G055905, GRMZM2G058158, and GRMZM2G171365 showed that their expression level is similar to the flowering time genes, which playing a key role in maize flowering time transition. This study revealed that the changes of flowering time in mass selection process may be strongly associated with the variations of allele frequency changes, and we identified some important candidate genes for flowering time, which will provide a new insight for the rapid improvement of maize important agronomic traits and promote the gene cloning of maize flowering time.

Some New Methodological and Conceptual Aspects of the "Acid Growth Theory" for the Auxin Action in Maize (Zea mays L.) Coleoptile Segments: Do Acid- and Auxin-Induced Rapid Growth Differ in Their Mechanisms?

Two arguments against the “acid growth theory” of auxin-induced growth were re-examined. First, the lack of a correlation between the IAA-induced growth and medium acidification, which is mainly due to the cuticle, which is a barrier for proton diffusion. Second, acid- and the IAA-induced growth are additive processes, which means that acid and the IAA act via different mechanisms. Here, growth, medium pH, and membrane potential (in some experiments) were simultaneously measured using non-abraded and non-peeled segments but with the incubation medium having access to their lumen. Using such an approach significantly enhances both the IAA-induced growth and proton extrusion (similar to that of abraded segments). Staining the cuticle on the outer and inner epidermis of the coleoptile segments showed that the cuticle architecture differs on both sides of the segments. The dose-response curves for the IAA-induced growth and proton extrusion were bell-shaped with the maximum at 10⁻⁴ M over 10 h. The kinetics of the IAA-induced hyperpolarisation was similar to that of the rapid phase of the IAA-induced growth. It is also proposed that the K⁺/H⁺ co-transporters are involved in acid-induced growth and that the combined effect of the K⁺ channels and K⁺/ H⁺ co-transporters is responsible for the IAA-induced growth. These findings support the “acid growth theory” of auxin action.

Global transcriptional profiling between inbred parents and hybrids provides comprehensive insights into ear-length heterosis of maize (Zea mays)

BACKGROUND

Maize (Zea mays) ear length, which is an important yield component, exhibits strong heterosis. Understanding the potential molecular mechanisms of ear-length heterosis is critical for efficient yield-related breeding.

RESULTS

Here, a joint netted pattern, including six parent-hybrid triplets, was designed on the basis of two maize lines harboring long (T121 line) and short (T126 line) ears. Global transcriptional profiling of young ears (containing meristem) was performed. Multiple comparative analyses revealed that 874 differentially expressed genes are mainly responsible for the ear-length variation between T121 and T126 lines. Among them, four key genes, Zm00001d049958, Zm00001d027359, Zm00001d048502 and Zm00001d052138, were identified as being related to meristem development, which corroborated their roles in the superior additive genetic effects on ear length in T121 line. Non-additive expression patterns were used to identify candidate genes related to ear-length heterosis. A non-additively expressed gene (Zm00001d050649) was associated with the timing of meristematic phase transition and was determined to be the homolog of tomato SELF PRUNING, which assists SINGLE FLOWER TRUSS in driving yield-related heterosis, indicating that Zm00001d050649 is a potential contributor to drive heterotic effect on ear length.

CONCLUSION

Our results suggest that inbred parents provide genetic and heterotic effects on the ear lengths of their corresponding F₁ hybrids through two independent pathways. These findings provide comprehensive insights into the transcriptional regulation of ear length and improve the understanding of ear-length heterosis in maize.

An updated census of the maize TIFY family

The TIFY gene family is a plant-specific gene family encoding a group of proteins characterized by its namesake, the conservative TIFY domain and members can be organized into four subfamilies: ZML, TIFY, PPD and JAZ (Jasmonate ZIM-domain protein) by presence of additional conserved domains. The TIFY gene family is intensively explored in several model and agriculturally important crop species and here, yet the composition of the TIFY family of maize has remained unresolved. This study increases the number of maize TIFY family members known by 40%, bringing the total to 47 including 38 JAZ, 5 TIFY, and 4 ZML genes. The majority of the newly identified genes were belonging to the JAZ subfamily, six of which had aberrant TIFY domains, suggesting loss JAZ-JAZ or JAZ-NINJA interactions. Six JAZ genes were found to have truncated Jas domain or an altered degron motif, suggesting resistance to classical JAZ degradation. In addition, seven membranes were found to have an LxLxL-type EAR motif which allows them to recruit TPL/TPP co-repressors directly without association to NINJA. Expression analysis revealed that ZmJAZ14 was specifically expressed in the seeds and ZmJAZ19 and 22 in the anthers, while the majority of other ZmJAZs were generally highly expressed across diverse tissue types. Additionally, ZmJAZ genes were highly responsive to wounding and JA treatment. This study provides a comprehensive update of the maize TIFY/JAZ gene family paving the way for functional, physiological, and ecological analysis.

Prediction of Crop Yield Using Phenological Information Extracted from Remote Sensing Vegetation Index

Phenology is an indicator of crop growth conditions, and is correlated with crop yields. In this study, a phenological approach based on a remote sensing vegetation index was explored to predict the yield in 314 counties within the US Corn Belt, divided into semi-arid and non-semi-arid regions. The Moderate Resolution Imaging Spectroradiometer (MODIS) data product MOD09Q1 was used to calculate the normalized difference vegetation index (NDVI) time series. According to the NDVI time series, we divided the corn growing season into four growth phases, calculated phenological information metrics (duration and rate) for each growth phase, and obtained the maximum correlation NDVI (Max-R2). Duration and rate represent crop growth days and rate, respectively. Max-R2 is the NDVI value with the most significant correlation with corn yield in the NDVI time series. We built three groups of yield regression models, including univariate models using phenological metrics and Max-R2, and multivariate models using phenological metrics, and multivariate models using phenological metrics combined with Max-R2 in the whole, semi-arid, and non-semi-arid regions, respectively, and compared the performance of these models. The results show that most phenological metrics had a statistically significant (p < 0.05) relationship with corn yield (maximum R2 = 0.44). Models established with phenological metrics realized yield prediction before harvest in the three regions with R2 = 0.64, 0.67, and 0.72. Compared with the univariate Max-R2 models, the accuracy of models built with Max-R2 and phenology metrics improved. Thus, the phenology metrics obtained from MODIS-NDVI accurately reflect the corn characteristics and can be used for large-scale yield prediction. Overall, this study showed that phenology metrics derived from remote sensing vegetation indexes could be used as crop yield prediction variables and provide a reference for data organization and yield prediction with physical crop significance.

Genetic diversity and population structure of early and extra-early maturing maize germplasm adapted to sub-Saharan Africa

BACKGROUND

Assessment and effective utilization of genetic diversity in breeding programs is crucial for sustainable genetic improvement and rapid adaptation to changing breeding objectives. During the past two decades, the commercialization of the early and extra-early maturing cultivars has contributed to rapid expansion of maize into different agro-ecologies of sub-Saharan Africa (SSA) where maize has become an important component of the agricultural economy and played a vital role in food and nutritional security. The present study aimed at understanding the population structure and genetic variability among 439 early and extra-early maize inbred lines developed from three narrow-based and twenty-seven broad-based populations by the International Iinstitute of Tropical Agriculture Maize Improvement Program (IITA-MIP). These inbreds were genotyped using 9642 DArTseq-based single nucleotide polymorphism (SNP) markers distributed uniformly throughout the maize genome.

RESULTS

About 40.8% SNP markers were found highly informative and exhibited polymorphic information content (PIC) greater than 0.25. The minor allele frequency and PIC ranged from 0.015 to 0.500 and 0.029 to 0.375, respectively. The STRUCTURE, neighbour-joining phylogenetic tree and principal coordinate analysis (PCoA) grouped the inbred lines into four major classes generally consistent with the selection history, ancestry and kernel colour of the inbreds but indicated a complex pattern of the genetic structure. The pattern of grouping of the lines based on the STRUCTURE analysis was in concordance with the results of the PCoA and suggested greater number of sub-populations (K = 10). Generally, the classification of the inbred lines into heterotic groups based on SNP markers was reasonably reliable and in agreement with defined heterotic groups of previously identified testers based on combining ability studies.

CONCLUSIONS

Complete understanding of potential heterotic groups would be difficult to portray by depending solely on molecular markers. Therefore, planned crosses involving representative testers from opposing heterotic groups would be required to refine the existing heterotic groups. It is anticipated that the present set of inbreds could contribute new beneficial alleles for population improvement, development of hybrids and lines with potential to strengthen future breeding programs. Results of this study would help breeders in formulating breeding strategies for genetic enhancement and sustainable maize production in SSA.

Molecular characterization, expression and functional analysis of acyl-CoA-binding protein gene family in maize (Zea mays)

BACKGROUND

Acyl-CoA-binding proteins (ACBPs) possess a conserved acyl-CoA-binding (ACB) domain that facilitates binding to acyl-CoA esters and trafficking in eukaryotic cells. Although the various functions of ACBP have been characterized in several plant species, their structure, molecular evolution, expression profile, and function have not been fully elucidated in Zea mays L.

RESULTS

Genome-wide analysis identified nine ZmACBP genes in Z. mays, which could be divided into four distinct classes (class I, class II, class III, and class IV) via construction of a phylogenetic tree that included 48 ACBP genes from six different plant species. Transient expression of a ZmACBP-GFP fusion protein in tobacco (Nicotiana tabacum) epidermal cells revealed that ZmACBPs localized to multiple different locations. Analyses of expression profiles revealed that ZmACBPs exhibited temporal and spatial expression changes during abiotic and biotic stresses. Eight of the nine ZmACBP genes were also found to have significant association with agronomic traits in a panel of 500 maize inbred lines. The heterologous constitutive expression of ZmACBP1 and ZmACBP3 in Arabidopsis enhanced the resistance of these plants to salinity and drought stress, possibly through alterations in the level of lipid metabolic and stress-responsive genes.

CONCLUSION

The ACBP gene family was highly conserved across different plant species. ZmACBP genes had clear tissue and organ expression specificity and were responsive to both biotic and abiotic stresses, suggesting their roles in plant growth and stress resistance.

Tree rows in temperate agroforestry croplands alter the composition of soil bacterial communities

BACKGROUND

Tree-based intercropping (agroforestry) has been advocated to reduce adverse environmental impacts of conventional arable cropping. Modern agroforestry systems in the temperate zone are alley-cropping systems that combine rows of fast-growing trees with rows of arable crops. Soil microbial communities in these systems have been investigated intensively; however, molecular studies with high taxonomical resolution are scarce.

METHODS

Here, we assessed the effect of temperate agroforestry on the abundance, diversity and composition of soil bacterial communities at three paired poplar-based alley cropping and conventional monoculture cropland systems using real-time PCR and Illumina sequencing of bacterial 16S rRNA genes. Two of the three systems grew summer barley (Hordeum vulgare); one system grew maize (Zea mays) in the sampling year. To capture the spatial heterogeneity induced by the tree rows, soil samples in the agroforestry systems were collected along transects spanning from the centre of the tree rows to the centre of the agroforestry crop rows.

RESULTS

Tree rows of temperate agroforestry systems increased the abundance of soil bacteria while their alpha diversity remained largely unaffected. The composition of the bacterial communities in tree rows differed from those in arable land (crop rows of the agroforestry systems and conventional monoculture croplands). Several bacterial groups in soil showed strong association with either tree rows or arable land, revealing that the introduction of trees into arable land through agroforestry is accompanied by the introduction of a tree row-associated microbiome.

CONCLUSION

The presence of tree row-associated bacteria in agroforestry increases the overall microbial diversity of the system. We speculate that the increase in biodiversity is accompanied by functional diversification. Differences in plant-derived nutrients (root exudates and tree litter) and management practices (fertilization and tillage) likely account for the differences between bacterial communities of tree rows and arable land in agroforestry systems.

Transgenic insertion of the cyanobacterial membrane protein ictB increases grain yield in Zea mays through increased photosynthesis and carbohydrate production

The C₄ crop maize (Zea mays) is the most widely grown cereal crop worldwide and is an essential feedstock for food and bioenergy. Improving maize yield is important to achieve food security and agricultural sustainability in the 21^st century. One potential means to improve crop productivity is to enhance photosynthesis. ictB, a membrane protein that is highly conserved across cyanobacteria, has been shown to improve photosynthesis, and often biomass, when introduced into diverse C₃ plant species. Here, ictB from Synechococcus sp. strain PCC 7942 was inserted into maize using Agrobacterium-mediated transformation. In three controlled-environment experiments, ictB insertion increased leaf starch and sucrose content by up to 25% relative to controls. Experimental field trials in four growing seasons, spanning the Midwestern United States (Summers 2018 & 2019) and Argentina (Winter 2018 & 2019), showed an average of 3.49% grain yield improvement, by as much as 5.4% in a given season and up to 9.4% at certain trial locations. A subset of field trial locations was used to test for modification of ear traits and ФPSII, a proxy for photosynthesis. Results suggested that yield gain in transgenics could be associated with increased ФPSII, and the production of longer, thinner ears with more kernels. ictB localized primarily to the microsome fraction of leaf bundle-sheath cells, but not to chloroplasts. Extramembrane domains of ictB interacted in vitro with proteins involved in photosynthesis and carbohydrate metabolism. To our knowledge, this is the first published evidence of ictB insertion into a species using C₄ photosynthesis and the largest-scale demonstration of grain yield enhancement from ictB insertion in planta. Results show that ictB is a valuable yield gene in the economically important crop maize, and are an important proof of concept that transgenic manipulation of photosynthesis can be used to create economically viable crop improvement traits.

Occurrence of Fusarium Mycotoxins and Their Modified Forms in Forage Maize Cultivars

Forage maize is often infected by mycotoxin-producing Fusarium fungi during plant growth, which represent a serious health risk to exposed animals. Deoxynivalenol (DON) and zearalenone (ZEN) are among the most important Fusarium mycotoxins, but little is known about the occurrence of their modified forms in forage maize. To assess the mycotoxin contamination in Northern Germany, 120 natural contaminated forage maize samples of four cultivars from several locations were analysed by liquid chromatography-high resolution mass spectrometry (LC-HRMS) for DON and ZEN and their modified forms deoxynivalenol-3-glucoside (DON3G), the sum of 3- and 15-acetyl-deoxynivalenol (3+15-AcDON), α- and β-zearalenol (α-ZEL, β-ZEL). DON and ZEN occurred with high incidences (100 and 96%) and a wide range of concentrations, reaching levels up to 10,972 and 3910 µg/kg, respectively. Almost half of the samples (46%) exceeded the guidance value in complementary and complete feeding stuffs for ZEN (500 µg/kg), and 9% for DON (5000 µg/kg). The DON related mycotoxins DON3G and 3+15-AcDON were also present in almost all samples (100 and 97%) with amounts of up to 3038 and 2237 µg/kg and a wide range of concentrations. For the ZEN metabolites α- and β-ZEL lower incidences were detected (59 and 32%) with concentrations of up to 423 and 203 µg/kg, respectively. Forage maize samples were contaminated with at least three co-occurring mycotoxins, whereby 95% of all samples contained four or more mycotoxins with DON, DON3G, 3+15-AcDON, and ZEN co-occurring in 93%, together with α-ZEL in 57% of all samples. Positive correlations were established between concentrations of the co-occurring mycotoxins, especially between DON and its modified forms. Averaged over all samples, ratios of DON3G/DON and 3+15-AcDON/DON were similar, 20.2 and 20.5 mol%; cultivar-specific mean ratios ranged from 14.6 to 24.3 mol% and 15.8 to 24.0 mol%, respectively. In total, 40.7 mol% of the measured DON concentration was present in the modified forms DON3G and 3+15-AcDON. The α-ZEL/ZEN ratio was 6.2 mol%, ranging from 5.2 to 8.6 mol% between cultivars. These results demonstrate that modified mycotoxins contribute substantially to the overall mycotoxin contamination in forage maize. To avoid a considerable underestimation, it is necessary to analyse modified mycotoxins in future mycotoxin monitoring programs together with their parent forms.

Optimization of training sets for genomic prediction of early-stage single crosses in maize

Training population optimization algorithms are useful for efficiently training genomic prediction models for single-cross performance, especially if the population is extended beyond only realized crosses to all possible single crosses. Genomic prediction of single-cross performance could allow effective evaluation of all possible single crosses between all inbreds developed in a hybrid breeding program. The objectives of the present study were to investigate the effect of different levels of relatedness on genomic predictive ability of single crosses, evaluate the usefulness of deterministic formula to forecast prediction accuracy in advance, and determine the potential for TRS optimization based on prediction error variance (PEVmean) and coefficient of determination (CDmean) criteria. We used 481 single crosses made by crossing 89 random recombinant inbred lines (RILs) belonging to the Iowa stiff stalk synthetic group with 103 random RILs belonging to the non-stiff stalk synthetic heterotic group. As expected, predictive ability was enhanced by ensuring close relationships between TRSs and target sets, even when TRS sizes were smaller. We found that designing a TRS based on PEVmean or CDmean criteria is useful for increasing the efficiency of genomic prediction of maize single crosses. We went further and extended the sampling space from that of all observed single crosses to all possible single crosses, providing a much larger genetic space within which to design a training population. Using all possible single crosses increased the advantage of the PEVmean and CDmean methods based on expected prediction accuracy. This finding suggests that it may be worthwhile using an optimization algorithm to select a training population from all possible single crosses to maximize efficiency in training accurate models for hybrid genomic prediction.

A novel way to validate UAS-based high-throughput phenotyping protocols using in silico experiments for plant breeding purposes

It is possible to make inferences regarding the feasibility and applicability of plant high-throughput phenotyping via computer simulations. Protocol validation has been a key challenge to the establishment of high-throughput phenotyping (HTP) in breeding programs. We add to this matter by proposing an innovative way for designing and validating aerial imagery-based HTP approaches with in silico 3D experiments for plant breeding purposes. The algorithm is constructed following a pipeline composed of the simulation of phenotypic values, three-dimensional modeling of trials, and image rendering. Our tool is exemplified by testing a set of experimental setups that are of interest in the context of maize breeding using a comprehensive case study. We report on how the choice of (percentile of) points in dense clouds, the experimental repeatability (heritability), the treatment variance (genetic variability), and the flight altitude affect the accuracy of high-throughput plant height estimation based on conventional structure-from-motion (SfM) and multi-view stereo (MVS) pipelines. The evaluation of both the algorithm and the case study was driven by comparisons of the computer-simulated (ground truth) and the HTP-estimated values using correlations, regressions, and similarity indices. Our results showed that the 3D experiments can be adequately reconstructed, enabling inference-making. Moreover, it suggests that treatment variance, repeatability, and the choice of the percentile of points are highly influential over the accuracy of HTP. Conversely, flight altitude influenced the quality of reconstruction but not the accuracy of plant height estimation. Therefore, we believe that our tool can be of high value, enabling the promotion of new insights and further understanding of the events underlying the practice of high-throughput phenotyping.

Transcriptome analysis reveals the mechanism of anthocyanidins biosynthesis during grains development in purple corn (Zea mays L.)

Anthocyanidins are important pigments that cause plant tissues to develop colors. They have attracted much attention due to their crucial regulatory roles in plant growth as well as their health benefits. In order to reveal the molecular mechanism of anthocyanidin synthesis and regulation in purple corn (Zea mays L.) in this study, purple corn 963 was used to compare differences in gene expression during three stages of grain development by transcriptome analysis. A total of 17,168 differentially expressed genes (DEGs) (7564 up-regulated and 9604 down-regulated DGEs) were identified. The DEGs were significantly enriched in "Phenylpropanoid biosynthesis", "Biosynthesis of secondary metabolites", and "Plant hormone signal transduction". In addition, 72 % of the structural genes that regulate anthocyanidin synthesis were up-regulated, and the transcription factors related to the accumulation of anthocyanidins were enriched during grain development. Moreover, the differential expression of phytohormone genes might also be an important factor in anthocyanidin accumulation. Transcriptomic analysis presents a molecular basis for the study of grain color changes in the three stages of grain development, and provides information for further research on the mechanism of anthocyanidin synthesis.