Developmental Stages Of Maize Research Articles

Genome-wide identification, expression profiling, and network analysis of AT-hook gene family in maize

AT-hook motif nuclear localized (AHL) genes have diverse but poorly understood biological functions. We identified and analyzed 37 AHL genes in maize. We also discovered four and one additional AHLs in rice and sorghum, respectively, besides those reported earlier. The maize AHLs were classified into two clades (A and B) and three distinct types (I, II, and III) as also reported in Arabidopsis. Phylogenetic and ortholog analyses showed that, while the evolutionary classification was conserved in plants, expansion of the AHL gene family in maize was accompanied with new biological functions. Gene structure analysis showed that, while all but one Type-I AHLs lacked an intron, origin of Type-II and Type-III AHLs was associated with the gain of introns suggesting evolutionarily distinct temporal and spatial expression patterns and, likely, neofunctionalization. Gene duplication analysis revealed that AHLs in maize expanded via dispersive duplication further supporting their functional diversity. To discern these functions, we analyzed 71 transcriptomes from diverse tissues and developmental stages of maize and classified AHLs into eight groups with distinct temporal/spatial expression profiles. Coexpression analysis implicated 5 AHLs and 33 novel genes in networks specific to endosperm, seed, root, leaf, and reproductive tissues indicating their role in the development of these organs. Major processes coregulated by AHLs include pollen development, drought response, senescence, and wound response. We also identified interactions of AHL proteins in coregulating important processes including stress response. These novel insights into the role of AHLs in plant development provide a platform for functional analyses in maize and related grasses.

Application of organomineral fertilizers sourced from filter cake and sewage sludge can affect nutrients and heavy metals in soil during early development of maize

This study determined the changes in soil nutrients, organic carbon, organic matter and heavy metals during the early development stages of maize fertilized with different sources and doses. Also, this study confirmed that the used biosolid in the formulation of organomineral fertilizer makes greater efficacy than the effects promoted by mineral or filter cake organomineral fertilizers already used in agricultural. The experiment was done in a greenhouse at the Federal University of de Uberlândia - Campus Umuarama. The experimental design was randomized block design, as a 2 x 5 + 2 factorial, containing two sources of organomineral fertilizer consisting of organic residues (biosolid and filter cake), five doses of organomineral fertilizer (60, 80, 100, 120 and 140% of P2O5 recommendation for maize crop), a positive control with mineral fertilization (100%) and a negative one with no fertilization with four replications. The soil pH and contents of phosphorus, potassium, calcium, magnesium base saturation, base sum, micronutrients, organic carbon, organic matter and heavy metals were determined subsequently after plant removal, 65 days after sowing. The organomineral fertilizers based on biosolid and filter cake yielded increases in phosphorus, boron and manganese in the soil, especially the biosolid source. Regardless of the fertilizer organic matter source, soil phosphorus increased linearly with increasing doses of the sources. Doses equal or below the recommendation for maize (100% P2O5) were less effective in supplying potassium. The organomineral sources did not add heavy metals to the soil. Fertilizers based on biosolid can supply nutrients, such as phosphorus, boron and manganese at high doses, replacing mineral fertilization, while maintaining and improving soil fertility with no contamination by heavy metals.

Use of drone with digital photographic machine embedded for determination of leaf cover

The normalized difference vegetation index (NDVI) obtained via radiometer is important to determine the physiological state of plant, being a promising tool for decision making as to the best time for the application of agricultural pesticides, to analyze the threshold of economic damage. The use of drones with digital camera embedded in agriculture is in broad expansion. Through digital images analyzed in computer programs and correlated with NDVI it is possible to determine the leafcover in plants. The aim of this study was to confirm the use of digital images at 30 m in height to determine the leaf cover, correlating them with NDVI values obtained on the ground. Therefore, 30 m height photos were taken with the help of a drone and three stages of maize development (N4, N8 and R1), which were considered as treatments; afterwards, the images were analyzed in software to survey the leaf cover. The NDVI data were obtained in the same areas at a height of 0.5 m from the crop canopy, and it were submitted to the Scott Knott Test at 5 % significance and Pearson correlation. There was no statistical difference between methods and the Pearson correlation coefficient value (0,952) confirms strong evidence for correlation between the two methods. Thus, it can be concluded that the use of drone with embedded digital camera has promising use for the determination of leaf cover in maize.

Tissue and nitrogen-linked expression profiles of ammonium and nitrate transporters in maize

BackgroundIn order to grow, plants rely on soil nutrients which can vary both spatially and temporally depending on the environment, the soil type or the microbial activity. An essential nutrient is nitrogen, which is mainly accessible as nitrate and ammonium. Many studies have investigated transport genes for these ions in Arabidopsis thaliana and recently in crop species, including Maize, Rice and Barley. However, in most crop species, an understanding of the participants in nitrate and ammonium transport across the soil plant continuum remains undefined.ResultsWe have mapped a non-exhaustive set of putative nitrate and ammonium transporters in maize. The selected transporters were defined based on previous studies comparing nitrate transport pathways conserved between Arabidopsis and Zea mays (Plett D et. al, PLOS ONE 5:e15289, 2010). We also selected genes from published studies (Gu R et. al, Plant and Cell Physiology, 54:1515-1524, 2013, Garnett T et. al, New Phytol 198:82-94, 2013, Garnett T et. al, Frontiers in Plant Sci 6, 2015, Dechorgnat J et. al, Front Plant Sci 9:531, 2018). To analyse these genes, the plants were grown in a semi-hydroponic system to carefully control nitrogen delivery and then harvested at both vegetative and reproductive stages. The expression patterns of 26 putative nitrogen transporters were then tested. Six putative genes were found not expressed in our conditions. Transcripts of 20 other genes were detected at both the vegetative and reproductive stages of maize development. We observed the expression of nitrogen transporters in all organs tested: roots, young leaves, old leaves, silks, cobs, tassels and husk leaves. We also followed the gene expression response to nitrogen starvation and resupply and uncovered mainly three expression patterns: (i) genes unresponsiveness to nitrogen supply; (ii) genes showing an increase of expression after nitrogen starvation; (iii) genes showing a decrease of expression after nitrogen starvation.ConclusionsThese data allowed the mapping of putative nitrogen transporters in maize at both the vegetative and reproductive stages of development. No growth-dependent expression was seen in our conditions. We found that nitrogen transporter genes were expressed in all the organs tested and in many cases were regulated by the availability of nitrogen supplied to the plant. The gene expression patterns in relation to organ specificity and nitrogen availability denote a speciality of nitrate and ammonium transporter genes and their probable function depending on the plant organ and the environment.

Assessment of maize yield and phenology by drone-mounted superspectral camera

The capability of unmanned aerial vehicle (UAV) spectral imagery to assess maize yield under full and deficit irrigation is demonstrated by a Tetracam MiniMCA12 11 bands camera. The MiniMCA12 was used to image an experimental field of 19 maize hybrids. Yield prediction models were explored for different maize development stages, with the best model found using maize plant development stage reproductive 2 (R2) for both maize grain yield and ear weight (respective R2 values of 0.73 and 0.49, and root mean square error of validation (RMSEV) values of 2.07 and 3.41 metric tons per hectare using partial least squares regression (PLS-R) validation models). Models using vegetation indices for inputs rather than superspectral data showed similar R2 but higher RMSEV values, and produced best results for the R4 development stage. In addition to being able to predict yield, spectral models were able to distinguish between different development stages and irrigation treatments. These abilities potentially allow for yield prediction of maize plants whose development stage and water status are unknown.

Farmers’ knowledge, perceptions and management practices for termite pests of maize in Southern Benin

Abstract Termite (Isoptera: Termitidae) infestation is an important constraint of maize production in Benin. A survey of 300 households was conducted in 2018 throughout 30 villages in Southern Benin to evaluate farmers’ knowledge, perceptions and management practices of maize termite pests using focus group discussions and individual interviews with a semi-structured questionnaire. The results showed that for most of the farmers, maize is the most susceptible crop to termite attacks and the maturation developmental stage having the highest termite abundance and damage. A total of 43 different names of maize termite pests corresponding to 8 species were recorded in the study area. Size and colour were the main criteria used by farmers to classify and identify maize termite pests. Amitermes evuncifer was perceived as the most damaging to maize during vegetative and maturation stages, while Macrotermes bellicosus was perceived by famers (32.5%) as most damaging during seedling and flowering maize development stages. Erratic rainfall was perceived by maize producers as the most important factor favouring termite infestation in maize fields. The majority of the local maize is considered by farmers as susceptible to termites. The use of synthetic insecticides was the main method to control termites. Four of the 20 pesticides used by farmers have active ingredients that have been listed as highly hazardous (class Ib) by the World Health Organization (WHO). Farmers training on the danger and impact of misuse of insecticides on the development of termite insecticide resistance was recommended. The development of an integrated termite management strategy is discussed and the future research for its implementation identified.

Methodological approach for predicting and mapping the phenological adaptation of tropical maize (Zea mays L.) using multi-environment trials

BackgroundThe phenological development of the maize crop from emergence through flowering to maturity, usually expressed as a rate (i.e. 1/duration), is largely controlled by temperature in the tropics. Maize plant phenological responses vary between varieties and quantifying these responses can help in predicting the timing and duration of critical periods for crop growth that affect the quality and quantity of seed. We used routine multi-environment trials data of diverse tropical maize varieties to: (1) fit 82 temperature dependent phenology models and select the best model for an individual variety, (2) develop a spatial framework that uses the phenology model to predict at landscape level the length of the vegetative and reproductive phases of diverse varieties of maize in different agro-ecologies. Multi-environment trial data of 22 maize varieties from 16 trials in Kenya, Ethiopia, and Sudan was analyzed and the Levenberg–Marquardt algorithm combined with statistical criteria was applied to determine the best temperature-dependent model.ResultsThe Briere model, which is not often used in plant phenology, provided the best fit, with observed and predicted days to flowering showing good agreement. Linking the model with temperature and scaling out through mapping gave the duration from emergence to maturity of different maize varieties in areas where maize could potentially be grown.ConclusionThe methodology and framework used in the study provides an opportunity to develop tools that enhance farmers’ ability to predict stages of maize development for efficient crop management decisions and assessment of climate change impacts. This methodology could contribute to increase maize production if used to identify varieties with desired maturity for a specific agro-ecology in in the targeted regions.

Unpacking the push-pull system: Assessing the contribution of companion crops along a gradient of landscape complexity

The push-pull system, a stimulo-deterrent cropping strategy consisting of intercropping cereals with herbaceous legumes and surrounded by fodder grasses, is presented as a promising crop diversification strategy for smallholder farmers in Africa as it may contribute to maize stemborer Busseola fusca (Fuller) suppression, while improving soil fertility and providing feed for livestock. The push-pull system has often been assessed at plot level and as a package (e.g., Maize + Desmodium + Napier grass). However, it is unclear how the system performs in different landscape settings or when companion crops are changed to better meet household needs. Here we evaluate the potential of the push-pull system to suppress maize stemborer infestations in three landscapes in the Rift Valley region of Ethiopia along a gradient of landscape complexity. Within each landscape, experimental plots were established on four representative smallholder farms. At each farm we used a split-plot factorial design with main plots surrounded or not by Napier grass, and subplots consisting of sole maize, maize-bean or maize-Desmodium. We assessed stemborer infestation level and maize grain and stover yields during two years, as well as natural enemies abundance and egg predation at two maize development stages in the second year. In the simple landscape, which was dominated by maize, all treatments had high stemborer infestation levels, irrespective of within-field crop diversity; the presence of Napier grass was associated with higher predator abundance, while egg predation rates were the highest in the maize-bean intercrop. In the intermediate complexity landscape, subplots with sole maize had higher stemborer infestation levels compared to maize-bean or maize-Desmodium. In the complex landscape, infestation levels were low in all treatments. However, none of these effects led to significant differences in maize grain and stover yields among treatments in any of the landscapes. The benefits of the push-pull system accrued from the companion crops (bean, Desmodium and Napier), rather than from stemborer suppression per se. Our findings highlight the importance of the surrounding landscape in mediating the performance of the push-pull system, provide new insights on the contribution of the different components of push-pull system and can guide the design of ecologically intensive agroecosystems.

MAIZE CROP PHYTOTOXICITY IN RESPONSE TO SUB-DOSES OF SULFOMETURON-METHYL

ABSTRACT The use of ripeners has been a common practice in the sugarcane culture. The application of these products is often performed through aerial spraying, which increases the chances of drifting of the ripeners- molecules over the surrounding crops, such as maize. In order to study possible phytointoxication on maize caused by sulfometuron-methyl application, a field experiment was conducted to evaluate the effects of sulfometuron-methyl sub doses on maize when applied at the V4 and V8 development stages. The experiment was installed in a randomized block design with four replications. The treatments followed a 2 x 5 factor scheme, with the first factor corresponding to development stages of maize during which the ripener was applied (V4 and V8) and the second factor was related to sulfometuronmethyl sub doses (0; 0.45; 0.90; 1.35 and 1.80 g a.i. ha 1). The maize crop showed phytotoxicity with the use of 0.45 g a.i. ha-1 of sulfometuron-methyl; it was more severe when the application occurred at the development stage V8, leading the plant to death at the highest used dose. Furthermore, it was also possible to observe negative changes in the morphological and production components of maize plants. The SYN 7G17 maize hybrid is highly susceptible to sulfometuron-methyl. The occurrence of sulfometuron-methyl deposits at higher doses or at different development stages of the crop may reflect more severe phytotoxic effects than the ones observed in this study.

Maize response to time of nitrogen application and planting seasons

Nitrogen (N) response by maize differs due to growing seasons, growth stages, duration and growing domain as N losses is higher due to leaching as well as volatilization. Objective of this study was to know the response of split applications of N and growing seasons on maize under Chitwan environments. Field experiments were conducted for two consecutive years at the research field of NMRP Rampur during the winter, spring, and summer seasons of 2012/013 and 2013/014. Experiments were laid out in factorial randomized complete block design with four replications for all the seasons. Early maturing maize genotype Arun-1 EV was used for the experiments. Five splits of recommended dose of N were tested. Grain yield, days to flowering, plant height, ear height, kernel rows per ear, no. of kernels per row, ear length and thousand grain weight significantly differed due to growing seasons and split applications of N. Significantly higher grain yield (3911 kg ha-1) was obtained with the application of 30 kg N ha-1 each at 30, 45, 60, and 75 days after sowing as compared to control (2801 kg ha-1). Regarding the growing seasons, highest grain yield was obtained in winter (4393 kg ha-1) followed by spring (3791 kg ha-1) and summer (2468 kg ha-1) season, respectively. Results of these studies revealed that four splits of N viz. application of 30 kg N each at 30, 45, 60, and 75 days after sowing respectively, would be more economical to minimize N losses from the soil and efficient use of N at critical growth and development stages of maize.

Characterization of Genes Involved in Isoprenoid Diphosphate Biosynthesis in Maize

Terpenoids are the largest class of secondary metabolites with indispensable functions for plant growth and development. Maize is a very important cereal crop that is grown widely throughout the world. However, many genes and gene family members involved in terpenoid biosynthesis are still unknown in maize. Through systematic analysis, 43 isoprenoid diphosphate biosynthesis-related genes were identified. These genes are members of 15 families, which encode all of the enzymes involved in the biosynthesis of the universal isoprene precursor isopentenyl diphosphate and its isomer dimethylallyl diphosphate. Using a comprehensive approach, the intron/exon structures and their responses to jasmonic acid treatment were investigated. Meta-analysis revealed that some of the genes show differential, organ-specific expression patterns in the 60 different developmental stages of maize. It was found that all 2-C-methyl-d-erythritol 4-phosphate (MEP) pathway genes present the same expression patterns which were highly expressed in leaves and showed the lowest expression in seed. All investigated MEP pathway enzymes are localized in plastids by transient assay using Arabidopsis cells. In addition, some of the enzymes, such as acetyl-CoA C-acetyltransferase, hydroxymethylglutaryl-CoA reductase, and geranylgeranyl diphosphate synthase, are encoded by multiple gene members with different expression patterns, and both homomeric and heteromeric geranyl diphosphate synthases exist in maize. The results reveal the complexity of terpenoid biosynthesis and the existence of metabolic channels for diverse terpenoids in maize.

Response of stomatal density and bound gas exchange in leaves of maize to soil water deficit

Stomatal behavior in response to drought has been the focus of intensive research, but less attention has been paid to stomatal density. In this study, 5-week-old maize seedlings were exposed to different soil water contents. Stomatal density and size as well as leaf gas exchange were investigated after 2-, 4- and 6-week of treatment, which corresponded to the jointing, trumpeting, and filling stages of maize development. Results showed that new stomata were generated continually during leaf growth. Reduced soil water content significantly stimulated stomatal generation, resulting in a significant increase in stomatal density but a decrease in stomatal size and aperture. Independent of soil water conditions, stomatal density and length in the trumpeting and filling stages were greater than in the jointing stage. Irrespective of growth stage, severe water deficit significantly reduced stomatal conductance (G s), decreasing the leaf transpiration rate (T r) and net photosynthetic rate (P n). Stomatal density was significantly negatively correlated with both P n and T r but more strongly with T r, so the leaf instantaneous water use efficiency (WUE i ) correlated positively with stomatal density. In conclusion, drought led to a significant increase in stomatal density and a reduction in stomatal size and aperture, resulting in decreased P n and T r. Because the negative correlation of stomatal density to T r was stronger than that to P n, leaf WUE i tended to increase.

English

Leaf area development at early stages of plant growth affects dry matter production because the former is the determinant for the amount of light intercepted, which then is used for photosynthesis. A pot experiment was conducted in a glasshouse to investigate the interacting effect of soil types and nutrient levels on leaf area and leaf dry weight at early development stages of maize, bean, and sunflower. The experiment was laid down in a randomized complete block design with three factors including plant species, nutrient levels and soil types. The latter two showed an interacting effect both on leaf area per pot and leaf dry weight, but the three way interactions were not significant. Leaf area and leaf dry weight per pot were high in pot soils and at 50% nutrient level for all the plant types. All plant types showed higher difference in leaf area and leaf dry weight per pot in pot soil than in quartz sand and sandy soils. Leaf area per pot and leaf dry weight per pot was high in pot soils. Maize and bean, and maize and sunflower interactions showed significantly higher difference in leaf area and leaf dry weight in pot soil than in quartz sand and sandy soils.   Key words: Pot soil, quartz sand and sandy soils, plant types.

The impacts of spring basal and side dressing on maize yield

The yield potential of maize is very high. According to Tollenaar (1983), maize yield potential is as high as 25 t ha-1 (absolute dry yield) which is the highest among all cereals. In order to fully utilise this high yield potential, proper nutrient replenishment is of chief importance among all agrotechnical factors.
 The aim of research was to examine the effect of nitrogen fertiliser applied as basal and side dressing on maize yield.
 The measurements were performed at the Látókép experiment site (47° 33’ N, 21° 26’ E, 111 m asl) of the Centre for Agricultural Sciences of the University of Debrecen on mid-heavy calcareous chernozem soil with deep humus layer in an established experiment in 2011, 2012 and 2013. The trial design was split-split-plot with two replications.
 Based on the experiment results, it can be established that the nutrient uptake of maize is greatly dependent on the amount of water store in the soil. From the aspect of the development of the maize plant and water supply, the most determinant factor was the distribution of precipitation over the growing season and not the amount precipitation. This is shown by the fact there was only 276 mm precipitation – which was favourably distributed – in 2012 to increase the availability of nutrients and the main average was the highest in this year (14.394 t ha-1).
 Spring basal dressing helped maize development in all three years even on chernozem soil which is well supplied with nutrients. Although the effect of side dressing did not result in any yield increase, it could still contribute to mitigating the stress effects caused by environmental factors. Altogether, nutrient supply adapted to the various development stages of maize can favourably affect the success of maize production.

Relationships between gross primary production, green LAI, and canopy chlorophyll content in maize: Implications for remote sensing of primary production

Life on Earth depends on photosynthesis. Photosynthetic systems evolved early in Earth history, providing evidence for the significance of pigments in plant functions. Photosynthetic pigments fill multiple roles from increasing the range of energy captured for photosynthesis to protective functions. Given the importance of pigments to plant functioning, greater effort is needed to determine and quantify the relationship between gross primary production (GPP) and canopy chlorophyll (Chl) content, the main photosynthetic pigment, as well as its proxy, green leaf area index (GLAI), both used as quantitative measures of plant greenness. The objective of this study is to establish relationships for GPP vs. canopy Chl content and GPP vs. GLAI in maize. The main focus of the paper is to reveal fine details of the relationships and understand their features in different stages of maize development. Data on GPP, leaf Chl content and GLAI were collected across ten years (2001–2010) at three AmeriFlux sites in Nebraska over irrigated and rainfed maize. Relationships of GPP vs. total canopy Chl content and GPP vs. GLAI were established for vegetative, tasseling and reproductive stages. In each stage, relationships were close with determination coefficients above 0.9; however, the shapes and slopes of the relationships in vegetative stages were different from reproductive stages. This difference was more pronounced for the GPP vs. GLAI relationship. In part, this difference is due to different leaf Chl contents in vegetative and reproductive stages. Smaller but detectable differences in shape and slope were also found for the GPP vs. canopy Chl relationship. Despite the differences in relationships for vegetative and reproductive stages, for the entire growing season, green LAI (GLAI) explained 90% of GPP variation with a coefficient of variation (CV)=17%, while total canopy Chl content explained more than 92% of GPP variation with CV=15%. Quantitative characterization of relationships between GPP and such biophysical characteristics as GLAI and canopy Chl content underlines the role of chlorophyll in photosynthesis and has significant implications on remote sensing of primary production.

Analysis of the relationship between the spectral characteristics of maize canopy and leaf area index under drought stress

Maize is one of the most widespread grain crops in the world; however, more than 70% of corn in China suffers some degree of drought disaster every year. Leaf area index (LAI) is an important biophysical parameter of the vegetation canopy and has important significance for crop yield estimation. Using the data of canopy spectral reflectance and leaf area index (LAI) for maize plants experiencing different levels of soil moisture from 2011 to 2012, the characteristics of the canopy reflective spectrum and its first derivative, and their relationships to leaf area index, were analyzed. Soil moisture of the control group was about 75% while that of the drought stress treatment was about 45%. In addition, LAI retrieval models for maize were established using vegetation indices (VIs) and principal component analysis (PCA) and the models were tested using independent datasets representing different soil water contents and different developmental stages of maize. The results showed that canopy spectral reflectances were in accordance with the characteristics of green plants, under both drought stress and at different developmental stages. In the visible band, canopy reflectance for both healthy and damaged vegetation had a green-wavelength peak and a red-wavelength valley; reflectance under drought stress, especially in the green peak (about 550nm) and the red valley (about 676nm) was higher than in the control group. In the near-infrared band, the canopy spectral reflectance decreased substantially between 780 and 1350nm under drought stress. Moreover, the red edge of the spectrum was shifted toward blue wavelengths. The first derivative spectrum showed a double peak phenomenon at the edge of the red band at different developmental stages: the main peak appeared between 728 and 732nm and the minor peak at about 718nm. The double peaks become more obvious through the growth and development of the maize, with the most notable effect during the silking and milk stages, after which it gradually decreased. During maize growth, the LAI of all plants, regardless of soil moisture conditions, increased, and the largest LAI also occurred during the silking and milk stages. During those stages, the LAI of plants under different drought stress levels was significantly lower (by 20% or more) than in normal plants with sufficient water supplies. The LAI was highly significantly correlated with canopy spectral reflectance in the bands from 350nm to 510nm, from 571nm to 716nm, and from 1450nm to 1575nm. Also, the LAI was significantly correlated with red edge parameters and several VIs. The Perpendicular Vegetation Index (PVI) had the best correlation with LAI, with a coefficient of determination (R2) of 0.726 for the exponential correlation. Using dependent data, a LAI monitoring model for the maize canopy was constructed using PCA and VI methods. The test results showed that both the VI and PCA methods of monitoring maize LAI could provide robust estimates, with the predicted values of LAI being significantly correlated with the measured values. The model based on PVI showed higher precision under the drought stresses, with a correlation coefficient of 0.893 (n=27), while the model based on PCA was more precise under conditions of adequate soil moisture, with a correlation coefficient of 0.877 (n=32). Therefore, a synthesis of the models based on both VI and PCA could be more reliable for precisely predicting LAI under different levels of drought stresses in maize.

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

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

Trehalose Metabolism-Related Genes in Maize

Maize is a cereal crop that is grown widely throughout the world in a range of agro-ecological environments. Trehalose is a nonreducing disaccharide of glucose that has been associated with tolerance to different stress conditions, including salt and drought. Bioinformatic analysis of genes involved in trehalose biosynthesis and degradation in maize has not been reported to date. Through systematic analysis, 1 degradation-related and 36 trehalose biosynthesis-related genes were identified. The conserved domains and phylogenetic relationships among the deduced maize proteins and their homologs, isolated from other plant species such as Arabidopsis and rice, were revealed. Using a comprehensive approach, the intron/exon structures and expression patterns of all identified genes and their responses to salt stress, jasmonic acid, and abscisic acid treatment were analyzed. Microarray data demonstrated that some of the genes show differential, organ-specific expression patterns in the 60 different developmental stages of maize. It was discovered that some of the key enzymes such as hexokinase, trehalose-6-phosphate synthase, and trehalose-6-phosphate phosphatase are encoded by multiple gene members with different expression patterns. The results highlight the complexity of trehalose metabolism and provide useful information for improving maize stress tolerance through genetic engineering.

A Developmental Transcriptional Network for Maize Defines Coexpression Modules

Here, we present a genome-wide overview of transcriptional circuits in the agriculturally significant crop species maize (Zea mays). We examined transcript abundance data at 50 developmental stages, from embryogenesis to senescence, for 34,876 gene models and classified genes into 24 robust coexpression modules. Modules were strongly associated with tissue types and related biological processes. Sixteen of the 24 modules (67%) have preferential transcript abundance within specific tissues. One-third of modules had an absence of gene expression in specific tissues. Genes within a number of modules also correlated with the developmental age of tissues. Coexpression of genes is likely due to transcriptional control. For a number of modules, key genes involved in transcriptional control have expression profiles that mimic the expression profiles of module genes, although the expression of transcriptional control genes is not unusually representative of module gene expression. Known regulatory motifs are enriched in several modules. Finally, of the 13 network modules with more than 200 genes, three contain genes that are notably clustered (P < 0.05) within the genome. This work, based on a carefully selected set of major tissues representing diverse stages of maize development, demonstrates the remarkable power of transcript-level coexpression networks to identify underlying biological processes and their molecular components.

Why Early Season Weed Control Is Important in Maize

Control of early-emerging weeds is essential to protect the yield potential of maize. An understanding of the physiological changes that occur as a result of weed interference is required to address variability in yield loss across sites and years. Field trials were conducted at the University of Guelph (UG), the Ohio State University (OSU), and Colorado State University (CSU) during 2009 and 2010. There were six treatments (season-long weedy and weed-free, and weed control at the 1st-, 3rd-, 5th-, and 10th-leaf-tip stages of maize development) and 20 individual plants per plot were harvested at maturity. We hypothesized that, as weed control was delayed, weed interference in the early stages of maize development would increase plant-to-plant variability in plant dry-matter accumulation, which would result in a reduction of grain yield at maturity. The onset of the critical period for weed control (CPWC) occurred on average between the third and fifth leaf tip stages of development (i.e., V1 to V3, respectively). Rate of yield loss following the onset of the CPWC ranged from 0.05 MG ha−1d−1at UG 2009 to 0.22 MG ha−1d−1at CSU 2010 (i.e., 0.5 and 1.6% d−1, respectively). On average, reductions in kernel number per plant accounted for approximately 65% of the decline in grain yield as weed control was delayed. Biomass partitioning to the grain was stable through early weed removal treatments, increased and peaked at the 10th-leaf-tip time of control, and decreased in the season-long weedy treatment. Plant-to-plant variability in dry matter at maturity and incidence of bareness increased as weed control was delayed. As weed control was delayed, the contribution of plant-to-plant variability at maturity to the overall yield loss was small, relative to the decline of mean plant dry matter.