Inbred Line B73 Research Articles

Effects of histone methylation modification on low temperature seed germination and growth of maize

Low temperature is a limiting factor of seed germination and plant growth. Although there is a lot information on the response of maize to low temperatures, there is still poorly description of how histone methylation affects maize germination and growth development at low temperatures. In this study, the germination rate and physiological indexes of wild-type maize inbred lines B73 (WT), SDG102 silencing lines (AS), SDG102 overexpressed lines (OE) at germination stage and seedling stage were measured under low temperature stress (4 ℃), and transcriptome sequencing was applied to analyze the differences of gene expression in panicle leaves among different materials. The results showed that the germination rate of WT and OE maize seeds at 4 ℃ was significantly lower than 25 ℃. The content of MDA, SOD and POD of 4 ℃ seeding leaves higher than contrast. Transcriptome sequencing results showed that there were 409 different expression genes (DEGs) between WT and AS, and the DEGs were mainly up-regulated expression in starch and sucrose metabolism and phenylpropanoid biosynthesis. There were 887 DEGs between WT and OE, which were mainly up-regulated in the pathways of plant hormone signal transduction, porphyrin and chlorophyll metabolism. This result could provide a theoretical basis for analyzing the growth and development of maize from the perspective of histone methylation modification.

De novo transcriptome assembly from the nodal root growth zone of hydrated and water-deficit stressed maize inbred line FR697

Certain cultivars of maize show increased tolerance to water deficit conditions by maintenance of root growth. To better understand the molecular mechanisms related to this adaptation, nodal root growth zone samples were collected from the reference inbred line B73 and inbred line FR697, which exhibits a relatively greater ability to maintain root elongation under water deficits. Plants were grown under various water stress levels in both field and controlled environment settings. FR697-specific RNA-Seq datasets were generated and used for a de novo transcriptome assembly to characterize any genotype-specific genetic features. The assembly was aided by an Iso-Seq library of transcripts generated from various FR697 plant tissue samples. The Necklace pipeline was used to combine a Trinity de novo assembly along with a reference guided assembly and the Viridiplantae proteome to generate an annotated consensus “SuperTranscriptome” assembly of 47,915 transcripts with a N50 of 3152 bp in length. The results were compared by Blastn to maize reference genes, a Benchmarking Universal Single-Copy Orthologs (BUSCO) genome completeness report and compared with three maize reference genomes. The resultant ‘SuperTranscriptome’ was demonstrated to be of high-quality and will serve as an important reference for analysis of the maize nodal root transcriptomic response to environmental perturbations.

Genome-Wide Identification and Analysis of the Maize Serine Peptidase S8 Family Genes in Response to Drought at Seedling Stage.

Subtilisin-like proteases (subtilases) are found in almost all plant species and are involved in regulating various biotic and abiotic stresses. Although the literature on subtilases in different plant species is vast, the gene function of the serine peptidase S8 family and its maize subfamily is still unknown. Here, a bioinformatics analysis of this gene family was conducted by describing gene structure, conserved motifs, phylogenetic relationships, chromosomal distributions, gene duplications, and promoter cis-elements. In total, we identified 18 ZmSPS8 genes in maize, distributed on 7 chromosomes, and half of them were hydrophilic. Most of these proteins were located at the cell wall and had similar secondary and tertiary structures. Prediction of cis-regulatory elements in promoters illustrated that they were mainly associated with hormones and abiotic stress. Maize inbred lines B73, Zheng58, and Qi319 were used to analyze the spatial-temporal expression patterns of ZmSPS8 genes under drought treatment. Seedling drought results showed that Qi319 had the highest percent survival after 14 d of withholding irrigation, while B73 was the lowest. Leaf relative water content (LRWC) declined more rapidly in B73 and to lower values, and the nitrotetrazolium blue chloride (NBT) contents of leaves were higher in Qi319 than in the other inbreds. The qPCR results indicated that 6 serine peptidase S8 family genes were positively or negatively correlated with plant tolerance to drought stress. Our study provides a detailed analysis of the ZmSPS8s in the maize genome and finds a link between drought tolerance and the family gene expression, which was established by using different maize inbred lines.

Wide-Range Portrayal of AP2/ERF Transcription Factor Family in Maize (Zea mays L.) Development and Stress Responses.

The APETALA2/Ethylene-Responsive Transcriptional Factors containing conservative AP2/ERF domains constituted a plant-specific transcription factor (TF) superfamily, called AP2/ERF. The configuration of the AP2/ERF superfamily in maize has remained unresolved. In this study, we identified the 229 AP2/ERF genes in the latest (B73 RefGen_v5) maize reference genome. Phylogenetic classification of the ZmAP2/ERF family members categorized it into five clades, including 27 AP2 (APETALA2), 5 RAV (Related to ABI3/VP), 89 DREB (dehydration responsive element binding), 105 ERF (ethylene responsive factors), and a soloist. The duplication events of the paralogous genes occurred from 1.724-25.855 MYA, a key route to maize evolution. Structural analysis reveals that they have more introns and few exons. The results showed that 32 ZmAP2/ERFs regulate biotic stresses, and 24 ZmAP2/ERFs are involved in responses towards abiotic stresses. Additionally, the expression analysis showed that DREB family members are involved in plant sex determination. The real-time quantitative expression profiling of ZmAP2/ERFs in the leaves of the maize inbred line B73 under ABA, JA, salt, drought, heat, and wounding stress revealed their specific expression patterns. Conclusively, this study unveiled the evolutionary pathway of ZmAP2/ERFs and its essential role in stress and developmental processes. The generated information will be useful for stress resilience maize breeding programs.

A novel active transposon creates allelic variation through altered translation rate to influence protein abundance.

Protein translation is tightly and precisely controlled by multiple mechanisms including upstream open reading frames (uORFs), but the origins of uORFs and their role in maize are largely unexplored. In this study, an active transposition event was identified during the propagation of maize inbred line B73. The transposon, which was named BTA for 'B73 active transposable element hAT', creates a novel dosage-dependent hypomorphic allele of the hexose transporter gene ZmSWEET4c through insertion within the coding sequence in the first exon, and results in reduced kernel size. The BTA insertion does not affect transcript abundance but reduces protein abundance of ZmSWEET4c, probably through the introduction of a uORF. Furthermore, the introduction of BTA sequence in the exonof other genes can regulate translation efficiency without affecting their mRNA levels. A transposon capture assay revealed 79 novel insertions for BTA and BTA-like elements. These insertion sites have typical euchromatin features, including low levels of DNA methylation and high levels of H3K27ac. A putative autonomous element that mobilizes BTA and BTA-like elements was identified. Together, our results suggest a transposon-based origin of uORFs and document a new role for transposable elements to influence protein abundance and phenotypic diversity by affecting the translation rate.

Comparative Proteomic Analyses of Susceptible and Resistant Maize Inbred Lines at the Stage of Enations Forming following Infection by Rice Black-Streaked Dwarf Virus.

Rice black-streaked dwarf virus (RBSDV) is the main pathogen causing maize rough dwarf disease (MRDD) in China. Typical enation symptoms along the abaxial leaf veins prevail in RBSDV-infected maize inbred line B73 (susceptible to RBSDV), but not in X178 (resistant to RBSDV). Observation of the microstructures of epidermal cells and cross section of enations from RBSDV-infected maize leaves found that the increase of epidermal cell and phloem cell numbers is associated with enation formation. To identify proteins associated with enation formation and candidate proteins against RBSDV infection, comparative proteomics between B73 and X178 plants were conducted using isobaric tags for relative and absolute quantitation (iTRAQ) with leaf samples at the enation forming stage. The proteomics data showed that 260 and 316 differentially expressed proteins (DEPs) were identified in B73 and X178, respectively. We found that the majority of DEPs are located in the chloroplast and cytoplasm. Moreover, RBSDV infection resulted in dramatic changes of DEPs enriched by the metabolic process, response to stress and the biosynthetic process. Strikingly, a cell number regulator 10 was significantly down-regulated in RBSDV-infected B73 plants. Altogether, these data will provide value information for future studies to analyze molecular events during both enation formation and resistance mechanism to RBSDV infection.

Allele-specific Expression Reveals Multiple Paths to Highland Adaptation in Maize.

Maize is a staple food of smallholder farmers living in highland regions up to 4,000 m above sea level worldwide. Mexican and South American highlands are two major highland maize growing regions, and population genetic data suggest the maize's adaptation to these regions occurred largely independently, providing a case study for convergent evolution. To better understand the mechanistic basis of highland adaptation, we crossed maize landraces from 108 highland and lowland sites of Mexico and South America with the inbred line B73 to produce F1 hybrids and grew them in both highland and lowland sites in Mexico. We identified thousands of genes with divergent expression between highland and lowland populations. Hundreds of these genes show patterns of convergent evolution between Mexico and South America. To dissect the genetic architecture of the divergent gene expression, we developed a novel allele-specific expression analysis pipeline to detect genes with divergent functional cis-regulatory variation between highland and lowland populations. We identified hundreds of genes with divergent cis-regulation between highland and lowland landrace alleles, with 20 in common between regions, further suggesting convergence in the genes underlying highland adaptation. Further analyses suggest multiple mechanisms contribute to this convergence in gene regulation. Although the vast majority of evolutionary changes associated with highland adaptation were region specific, our findings highlight an important role for convergence at the gene expression and gene regulation levels as well.

Diversity in mitotic DNA repair efficiencies between commercial inbred maize lines and native Central American purple landraces

BackgroundHomologous recombination allows plants to repair double strand breaks in DNA, which if unrepaired may lead to cell death. In this project, we determined the relative DNA repair efficiency of the US inbred lines B73 and Mo17 and Central American purple landraces from Guatemala and Costa Rica with the purpose to uncover genetic differences that may allow for the breeding of new lines better adapted to tolerate DNA damage caused by environmental factors.MethodsSingle cell electrophoresis was used to analyze the relative DNA repair ability of several lines from the US and Central America exposed to radiomimetic agent Zeocin, and these results were in turn compared with High Resolution Melting analyses of key genes for homologous DNA recombination. The significance of differences between treatments was evaluated with the Di Rienzo, Guzmán and Casanoves (DGC) test, while High Resolution Melting and difference curves were generated with the R package “HRM.curve”. Curves were created as a negative first derivative (−d(RFU)/d(T)) using normalized relative fluorescence values (RFUs) after background removal. The kinase gene ZeaATM1 was amplified and sequenced in B73, Mo17, P1 and P2. Multiple sequence alignment of DNA and aminoacid sequences was performed using ClustalW. Protein sequence analysis was done in UniProt to compare the resulting aminoacid sequences from maize to the available sequences from Arabidopsis thaliana ecotype Col-0 (ATM protein code: Q9M3G7).ResultsSingle-cell electrophoresis results of statistical significance suggested that the landrace P1-Pujagua Santa Cruz is resistant to damage caused by the radiomimetic agent Zeocin, and landrace P2-Pujagua La Cruz was able to repair all DNA damage after 24 h of treatment and 1 h of recovery time. In contrast, line Mo17 was unable to repair the damage, but B73 and the landraces Jocopilas (Guatemalan), Orotina Congo, and Talamanca were partially able to repair the DNA damage. High resolution melting analysis of the putative homologous DNA repair gene ZeaATM1 revealed that landraces P1 and P2 may harbor polymorphisms for this gene, and P1 may harbor other polymorphisms for the transcription factor ZeaSOG1 as well as the tumor suppressor ZeaRAD51 and recombinase ZeaBRCA1. The kinase gene ZeaATM1 was sequenced, and results indicate that in lines P1 and P2 there are polymorphisms near and within the FATC domain, a domain required for the activation of ATM1-mediated repair of DNA damage.ConclusionsSignificant differences in DNA repair efficiency exist between inbred lines and landraces of maize and may be linked to allelic diversity in key genes for homologous recombination. Thus, Central American landraces could be used for breeding tolerance to genotoxic stress.

Determination of maize genotypes performance under water deficit using ISSR molecular index

Shortage of water is disastrous for crop production. The aim of this work is to obtain a group of maize inbred lines and hybrids that tolerates water deficit and collecting molecular characterizations for selection. This work was conducted in the 2019 and 2020. Five maize pure inbred lines B73, A132, NA30, S7 and DR-B1 were planted according to the design of half-diallel cross-breeding of the second Griffing method, and then 10 hybrids and 5 inbred lines were planted under the impact of irrigation intervals of 5, 10 and 15 days according to the Randomized Complete Block Design (RCBD) in split plot with 3 replicates. Results showed significance genotypes responses. The hybrid DR-B1 × S7 recorded the highest means of seed number per row (34.49 seed row-1), weight of 300 seed (80.77 g), and single plant yield (167.2 g). The shortest irrigation interval of 5 days recorded the highest number of seeds per row (35.39 seed row-1) and single plant yield (162.3 g). Similarity analysis showed a highest genetic diversity (lowest genetic similarity) was 0.83 between inbred 4 and 5. The highest genetic divergence (the least genetic similarity) between hybrids and inbred lines was 0.78 in inbred 4 and hybrid 3 x 2, while the highest genetic divergence of 0.92 was found between hybrids of 3 x 1 and 5 x 4. UPGMA analysis showed that inbred 5 (DR-B1) and inbred 4 (S7) in addition to 1×3, 1×2 and 1×4 hybrids high divergence. Therefore, yield components characteristics can be used for selection in breeding programmes and ISSR (inter simple sequence repeats) is a promising and efficient technique in identification of maize genotypes DNA molecular markers for water deficit tolerance selection.

Transcriptome analysis of maize pathogen Fusarium verticillioides revealed FvLcp1, a secreted protein with type-D fungal LysM and chitin-binding domains, that plays important roles in pathogenesis and mycotoxin production

Fusarium verticillioides is a key maize pathogen and produces fumonisins, a group of mycotoxins detrimental to humans and animals. Unfortunately, our understanding on how this fungus interacts with maize to trigger mycotoxin biosynthesis is limited. We performed a systematic computational network-based analysis of large-scale F. verticillioides RNA-seq datasets to identify gene subnetwork modules associated with virulence and fumonisin regulation. F. verticillioides was inoculated on two different maize lines, moderately resistant line hybrid 33K44 and highly susceptible line maize inbred line B73, to generate time-course RNA-Seq data. Among the highly discriminative subnetwork modules, we identified a putative hub gene FvLCP1, which encodes a putative a type-D fungal LysM protein with a signal peptide, three LysM domains, and two chitin binding domains. FvLcp1 is a unique protein that harbors these domains amongst five representative Fusarium species. FvLcp1 is a secreted protein important for fumonisin production with the LysM domain playing a critical role. The chitin-binding domain was essential for in vitro chitin binding. Using Magnaporthe oryzae, we learned that FvLcp1 accumulates in appressoria, suggesting that FvLcp1 is involved in host recognition and infection. Full length FvLcp1 suppressed BAX-triggered plant cell death in Nicotiana benthamiana. This unique type-D LysM secreted protein with a chitin-binding domain in F. verticillioides was shown to be potentially involved in suppressing host cell death and promoting fumonisin biosynthesis while the pathogen colonizes maize kernels.

Wearable Plant Sensor for In Situ Monitoring of Volatile Organic Compound Emissions from Crops.

Methanol is a major volatile organic compound (VOC) emitted from plants. Methanol emission reflects indirect plant defense against insects, promotes cell-to-cell communication, and adapts plants to various environmental stresses. This paper reports a wearable plant sensor that can monitor methanol emission directly on the leaf of a plant under field conditions with low cost, high portability, and easy installation and use. The sensor technology eliminates the need for complex sampling, expensive instruments, and skilled operators for conventional gas chromatography-mass spectrometry. The sensor uses a composite of conducting polymer microcrystallites and platinum nanoparticles (PtNPs). The conducting poly(2-amino-1,3,4-thiadiazole) or poly(ATD) provides a high electrocatalytic activity with redox behavior. The modification of poly(ATD) with catalytic PtNPs enables efficient electrochemical oxidation of methanol at a specific potential. The advantages of poly(ATD) and PtNPs are synergized for high sensitivity and selectivity of the sensor for detecting methanol emissions with a sub-ppm limit of detection. Further, the infusion of a polymer electrolyte into the porous electrode of the sensor enables an all-solid-state VOC sensor. The sensor is integrated into a miniature gas collection chamber and capped with a hydrophobic gas diffusion membrane to minimize the influence of environmental humidity on the sensor performance. The sensor is installed on the leaf surface. In situ detection shows a difference in methanol emission between the lower and upper leaves of greenhouse maize plants. Further, under field conditions, the sensor reveals a noticeable difference in methanol emission concentration between two genotypes (Mo17 and B73 inbred lines) of maize plants. Therefore, the sensor will provide a promising new means of directly monitoring volatile emission of plants, which is a physiological phenotype as a function of genes and environment.

Transcription factor ZmWRKY20 interacts with ZmWRKY115 to repress expression of ZmbZIP111 for salt tolerance in maize.

Maize (Zea mays) is an important cereal crop worldwide. However, its yield and quality are adversely affected by salt stress resulting from soil hypersalinity. Exploring the regulatory mechanisms of stress responses is of vital importance to increase maize seed production. In the present study, we screened ethyl methanesulfonate-induced maize mutants and identified a salt-tolerant mutant. A single base was mutated in ZmWRKY20, leading to the formation of a truncated protein variant. A detailed phenotypic analysis revealed that this mutant had significantly higher resistance to wilting and lower reactive oxygen species levels than the inbred line B73. ZmWRKY20 showed transcriptional activity in yeast and specifically bound W-boxes according to the results of our yeast one-hybrid, electrophoretic mobility shift, and dual-luciferase assays. Overexpression of ZmWRKY20 decreased salt tolerance in maize. Transcriptome profiling revealed that ZmWRKY20 overexpression extensively reprogrammed genes involved in regulating defense and oxidation-reduction responses. The results substantiate that ZmWRKY20 is directly targeted to the basic leucine zipper (bZIP) motif in the transcription factor ZmbZIP111. It was also verified that ZmWRKY20 interacts with ZmWRKY115 and both proteins act jointly to enhance ZmbZIP111 repression. The results indicate that the ZmWRKY20 and ZmWRKY115 transcription factors interact in the nucleus, leading to repression of ZmbZIP111 expression by directly binding its promoter, and increase the sensitivity of maize seedlings to salt stress. The current study improves our understanding of the complicated responses of maize to salt stress.

Identification of Fusarium verticillioides Resistance Alleles in Three Maize Populations With Teosinte Gene Introgression.

Fusarium ear rot (FER) is a common fungal disease in maize (Zea mays L.) caused by Fusarium verticillioides. Resistant germplasm resources for FER are rare in cultivated maize; however, teosintes (Z. mays ssp. parviglumis and Z. mays ssp. diploperennis), which are wild-type species of maize, have the potential to offer a novel source of resistance alleles to enhance pathogen resistance in modern maize. Therefore, the aim of this study was to identify favorable alleles that confer significant levels of resistance toward FER. Three populations of BC2F8 recombinant inbred lines (RILs) were developed by crossing two different teosintes, Z. diploperennis and Z. parviglumis, with maize inbred lines B73 and Zheng58, and were screened for FER resistance. We found that Z. diploperennis and Z. parviglumis had higher resistance toward F. verticillioides in the leaves than B73 and Zheng58. However, the resistance toward F. verticillioides in the leaf and ear was unrelated among RILs. FER resistance was positively correlated with grain yield in the B73 × diploperennis (BD) and Zheng58 × parviglumis (ZP) populations, partly because the quantitative trait loci (QTLs) of FER resistance and yield traits were located close together. Four coincident QTLs (qFERbd5.177, qFERbd10.140, qFERzp4.066, and qFERzp5.116) and two highly reliable resistance-yield synergistic QTLs (qFERbd10.140 and qFERzp4.066) were identified in the BD and ZP populations, opening up the possibility of breeding for FER resistance without reducing yield.

ZmMYC7 directly regulates ZmERF147 to increase maize resistance to Fusarium graminearum

The jasmonic acid (JA) signaling pathway is involved in plant growth, development, and response to abiotic or biotic stresses. MYC2, a bHLH transcription factor, is a regulatory hub in the pathway. The function of ZmMYC7, a putative MYC2 ortholog, in jasmonate-signaled defense responses of maize has not been reported. In this study, we found that ZmMYC7 possesses JID, TAD, bHLH and Zip domains and essential characteristics of transcription factors: a nuclear location and transactivation activity. The ZmMYC7 mutants showed markedly increased sensitivity to Fusarium graminearum and Setosphaeria turcica. The expression levels of the defense-associated genes ZmPR1, ZmPR2, ZmPR3, ZmPR5, ZmPR6, and ZmPR7 in response to F. graminearum infection were downregulated in ZmMYC7 mutants, while ZmPR4 and ZmPR10 were up-regulated. ZmMYC7 interacted with members of the ZmJAZ family, including ZmJAZ8, ZmJAZ11, and ZmJAZ12. ZmMYC7 physically interacted with G-box cis-elements in the ZmERF147 promoter in vitro and transcriptional activation of ZmERF147 by ZmMYC7 was inhibited by ZmJAZ11 and ZmJAZ12. ZmERF147 mutants were more susceptible to F. graminearum infection than inbred line B73 with concomitant down-regulation of all defense-associated ZmPRs except ZmPR4. These findings indicate that ZmMYC7 functions in maize resistance to F. graminearum and sheds light on maize defense responses to pathogenic fungi via the JA signaling pathway.

Genetic Analysis of Maternal Haploid Inducibility for In Vivo Haploid Induction in Maize

Doubled haploid (DH) technology based on in vivo haploid induction has gradually become the key technology in modern maize breeding. The ability of maternal germplasm to be induced into haploids, inducibility, varies among genotypes. To dissect the genetic basis of maternal haploid inducibility (MHI), an F2 population derived from inbred lines B73 and Zheng58 was used for single environment QTL analysis and QTL by environment interaction analysis. The mapping population was genotyped by the 48K liquid-phase hybridization probe capture technique and phenotyped in multi-environment trials for MHI. A total of ten QTLs located on chromosome bins 4.05, 4.09, 5.05/5.06, 6.07, 7.00, 7.01, 7.02, 7.03, 9.02, and 10.06 were identified for MHI. The PVE value of each QTL ranged from 4.79% to 10.01%. The QTL qMHI5 is a stable QTL identified in JSH, HN, and across environments with the highest PVE value of 10.01%. Three QTLs, qMHI4-1, qMHI5, and qMHI 9-1, were detected by both methods. Three genes, Zm00001d017366, Zm00001d017420, and Zm00001d017432, involved in seed development were the most likely candidate genes. This study provides valuable information for the genetic basis of MHI.

Molecular cloning of two maize (<italic>Zea mays</italic>) <italic>ZmCOP1</italic> genes and their transcription abundances in response to different light treatments

<p id="C3">As an E3 ubiquitin ligase, CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1) mediates ubiquitination and degradation of positive regulatory factors such as HY5, LAF1, HFR1, and CO of the light signal transduction in <italic>Arabidopsis thaliana</italic>, thus mediating seedling photomorphogenesis, anthocyanin synthesis, and flowering time. To explore functional differentiation of <italic>ZmCOP1</italic> genes, we cloned two <italic>ZmCOP1</italic> genes, designated as <italic>ZmCOP1a</italic> and <italic>ZmCOP1b</italic>, from maize inbred line B73 by reverse transcription PCR (RT-PCR). The physicochemical properties, domain prediction and phylogenetic tree of ZmCOP1 were analyzed by bioinformatics software and website. The transcription abundances of two <italic>ZmCOP1</italic> genes in different tissues and their responses to different light treatments at seedling stage were further analyzed by quantitative RT-PCR (qRT-PCR). We found that the open reading frames (ORFs) of <italic>ZmCOP1a</italic> and <italic>ZmCOP1b</italic> possessed 2082 and 2061 nucleotides, encoding 693 and 686 amino acids, respectively. The COP1 proteins of maize, rice, sorghum, millet, and <italic>Arabidopsis</italic> shared the same structural domains and high amino acid sequence identity, indicating that they may have similar functions. The two <italic>ZmCOP1</italic> genes were mainly expressed in the above-ground tissues. Both of them could rapidly respond to different light treatments, while the transcription abundances of <italic>ZmCOP1a</italic> were generally higher than those of <italic>ZmCOP1b</italic>. It might suggest that <italic>ZmCOP1a</italic> may play more important roles under different light conditions. Under long-day or short-day condition, the transcription abundances of both <italic>ZmCOP1a</italic> and <italic>ZmCOP1b</italic> during the dark phase were higher than those during the light phase. Another interesting case is that both genes kept similar expression patterns during the light phase, while, transcription abundances of <italic>ZmCOP1b</italic> were higher than those of <italic>ZmCOP1a</italic> during the dark phase. It might imply that <italic>ZmCOP1b</italic> may be more important than <italic>ZmCOP1a</italic> in response to long-day or short-day treatment. In conclusion, both <italic>ZmCOP1a</italic> and <italic>ZmCOP1b</italic> had got functional redundancy and differentiation. Both genes could participate in different light signal pathways, and regulate maize photomorphogenesis and flowering period. Our results also provide a research foundation for further exploration of two <italic>ZmCOP1</italic> genes and application in molecular breeding in maize.

Genetic mapping and prediction of flowering time and plant height in a maize Stiff Stalk MAGIC population.

The Stiff Stalk heterotic pool is a foundation of US maize seed parent germplasm and has been heavily utilized by both public and private maize breeders since its inception in the 1930s. Flowering time and plant height are critical characteristics for both inbred parents and their test crossed hybrid progeny. To study these traits, a 6-parent multiparent advanced generation intercross population was developed including maize inbred lines B73, B84, PHB47 (B37 type), LH145 (B14 type), PHJ40 (novel early Stiff Stalk), and NKH8431 (B73/B14 type). A set of 779 doubled haploid lines were evaluated for flowering time and plant height in 2 field replicates in 2016 and 2017, and a subset of 689 and 561 doubled haploid lines were crossed to 2 testers, respectively, and evaluated as hybrids in 2 locations in 2018 and 2019 using an incomplete block design. Markers were derived from a practical haplotype graph built from the founder whole genome assemblies and genotype-by-sequencing and exome capture-based sequencing of the population. Genetic mapping utilizing an update to R/qtl2 revealed differing profiles of significant loci for both traits between 635 of the DH lines and 2 sets of 570 and 471 derived hybrids. Genomic prediction was used to test the feasibility of predicting hybrid phenotypes based on the per se data. Predictive abilities were highest on direct models trained using the data they would predict (0.55-0.63), and indirect models trained using per se data to predict hybrid traits had slightly lower predictive abilities (0.49-0.55). Overall, this finding is consistent with the overlapping and nonoverlapping significant quantitative trait loci found within the per se and hybrid populations and suggests that selections for phenology traits can be made effectively on doubled haploid lines before hybrid data is available.

A Three-Year Plant Study of Salt-Tolerant Transgenic Maize Showed No Effects on Soil Enzyme Activity and Nematode Community.

The environmental effects of genetically modified crops are now a global concern. It is important to monitor the potential environmental impact of transgenic corn after commercial release. In rhizosphere soil, plant roots interact with soil enzymes and microfauna, which can be affected by the transgenes of genetically modified crops. To determine the long-term impact of transgenic plant cultivation, we conducted a field study for 3 consecutive years (2018–2020) and observed the enzyme activities and nematode populations in plots planted with transgenic maize BQ-2, non-transgenic wild-type maize (Qi319), and inbred line B73. We took soil samples from three cornfields at four different growth stages (V3, V9, R1, and R6 stages); determined soil dehydrogenase, urease, and sucrase activities; and collected and identified soil nematodes to the genus level. The results demonstrated seasonal variations in dehydrogenase, urease, and sucrase activities. However, there was a consistent trend of change. The generic composition and diversity indices of the soil nematodes did not significantly differ, although significant seasonal variation was found in the individual densities of the principal trophic groups and the diversity indices of the nematodes in all three cornfields. The results of the study suggest that a 3-year cultivation of transgenic corn had no significant effects on soil enzyme activity and the soil nematode community. This study provides a theoretical basis for the environmental impact monitoring of transgenic corn.

Genetic analysis and molecular characterization of a novel maize &amp;lt;italic&amp;gt;Bt2 &amp;lt;/italic&amp;gt;gene mutant

<p id="C3">The research of the molecular mechanism underlying maize kernel development is particularly important for the genetic improvement of maize yield and quality traits. In this study, we characterized a new shrunken kernel mutant <italic>5601Q</italic>, which was generated by a random transposon insertion. Genetic analysis indicated that the kernel phenotype was stably controlled by a single recessive gene. F₂ segregating population was constructed by crossing <italic>5601Q</italic> into B73 inbred line, and the mutant gene was located in the genetic interval of 60.19-62.58 Mb on chromosome 4. Sequence annotation showed that the <italic>BRITTLE ENDOSPERM2 </italic>(<italic>Bt2</italic>) gene, previously reported to be involved in maize kernel development, was located in this region. Maize<italic> Bt2</italic> gene encoded the small subunit of ADP-glucose pyrophosphorylase (AGPase), the first rate-limiting enzyme in the starch biosynthetic pathway of higher plants. Compared with wild type, 100-grain weight and starch content of mutant <italic>5601Q</italic> decreased significantly, but the soluble sugar content increased dramatically 4.67 times. We confirmed that <italic>5601Q</italic> was a new allele mutant of <italic>Bt2</italic> by allelic test of <italic>Bt2</italic> mutant <italic>1774 </italic>and<italic> 5601Q</italic>. Sequencing analysis revealed that <italic>Mutator 19 </italic>transposon was inserted in the 2nd exon of <italic>Bt2</italic> gene. In summary, our results indicated that the shrunken kernel in <italic>5601Q </italic>was caused by the loss-of-function of <italic>Bt2 </italic>gene, which provided a new germplasm resource to elucidate the mechanism of maize <italic>Bt2 </italic>gene in endosperm storage substance accumulation.

Transcriptomic Responses of Fall Armyworms (Spodoptera frugiperda) Feeding on a Resistant Maize Inbred Line Xi502 with High Benzoxazinoid Content

The fall armyworm (Spodoptera frugiperda) is a devastating invasive insect herbivore. Its success on its preferred host plant, maize (Zea mays), is supported by numerous specialized detoxification mechanisms that suppress the defense responses of maize. In this study, we used a resistant Chinese maize cultivar, Xi502, which showed slower growth and lower yield-related phenotypes compare with maize inbred line B73. Comparative transcriptomic analyses demonstrated that B73-fed fall armyworm larvae have a significantly faster transcriptomic re-configuration toward maturation compared to their siblings fed with Xi502 leaves, whereas a number of putative aromatic breakdown -related DEGs were specifically induced when feeding on Xi502. Targeted metabolomic quantification demonstrated that Xi502 contains significantly higher levels of various benzoxazinoid compounds. Artificial feeding with the structural analog of a benzoxazinoid compound preferentially accumulated in Xi502 demonstrated a significant growth inhibition effect on FAW larvae. These results provide important genetic material and preliminary evidence for further dissection of the FAW-resistance mechanism in maize.