Search

Maize is one of the most successful crops with regard to the utilization of heterosis. The haploid induction technique is one of the fastest methods to obtain pure maize material at the present stage. However, the molecular mechanism of haploid doubling is rarely reported. In this study, we treated B73 and ZNC442 haploid young shoots with colchicine for 0 h, 6.2 h, and 10 h, and analyzed the differentially expressed genes (DEGs). We found that colchicine treatment for 6.2 h and 10 h compared to 0 h resulted in a total of 4868 co-DEGs. GO enrichment analysis and KEGG metabolic pathway analysis found significantly enriched 282 GO terms and 31 significantly pathways, respectively. Additionally, The GO term and KEGG pathway genes of spindle, cytoskeleton, microtubules and nuclear division were selected for analysis, and three candidate genes were screened by taking intersections. Zm00001d033112, Zm00001d010525, and Zm00001d043386 were annotated as kinesin-associated protein 13, kinesin-like protein KIN-10C, and kinesin light-chain LC6, respectively. The real-time fluorescence quantification (RT-PCR) results revealed that Zm00001d033112, Zm00001d010525, and Zm00001d043386 had the same trends as RNA-seq. Interestingly, Zm00001d033112 is homologous gene AT3G20150 in Arabidopsis, which was involved in the regulation of chromosome movement and mitotic spindle assembly. Our study suggests that kinesin genes may play an important role in doubling chromosomes, thus providing valuable information for future studies on the molecular mechanisms of chromosome doubling in maize. [ABSTRACT FROM AUTHOR]

Phosphorus (P) deficiency is one of the most critical factors for plant growth and productivity, including its inhibition of lateral root initiation. Auxin response factors (ARFs) play crucial roles in root development via auxin signaling mediated by genetic pathways. In this study, we found that the transcription factor ZmARF1 was associated with low inorganic phosphate (Pi) stress-related traits in maize. This superior root morphology and greater phosphate stress tolerance could be ascribed to the overexpression of ZmARF1. The knock out mutant zmarf1 had shorter primary roots, fewer root tip number, and lower root volume and surface area. Transcriptomic data indicate that ZmLBD1, a direct downstream target gene, is involved in lateral root development, which enhances phosphate starvation tolerance. A transcriptional activation assay revealed that ZmARF1 specifically binds to the GC-box motif in the promoter of ZmLBD1 and activates its expression. Moreover, ZmARF1 positively regulates the expression of ZmPHR1, ZmPHT1;2, and ZmPHO2, which are key transporters of Pi in maize. We propose that ZmARF1 promotes the transcription of ZmLBD1 to modulate lateral root development and Pi-starvation induced (PSI) genes to regulate phosphate mobilization and homeostasis under phosphorus starvation. In addition, ZmERF2 specifically binds to the ABRE motif of the promoter of ZmARF1 and represses its expression. Collectively, the findings of this study revealed that ZmARF1 is a pivotal factor that modulates root development and confers low-Pi stress tolerance through the transcriptional regulation of the biological function of ZmLBD1 and the expression of key Pi transport proteins. Author summary: Phosphorus (P) is a critical macronutrient for plant growth and development. Root system architecture (RSA) affects the ability of plants to obtain water and mineral nutrients from soil. Several auxin response factors (ARFs) are involved in auxin signaling and lateral root (LR) formation in P-deficient plants, but the molecular mechanisms underlying P deficiency-induced changes in the RSA of maize is not well understood. We found that ZmARF1 positively regulates root development and confers tolerance to low inorganic phosphate (Pi) stress in maize. ZmARF1 regulates root development by interacting with the promoter of ZmLBD1 and positively regulating its expression. Furthermore, we empirically revealed that ZmARF1 enhanced Pi mobilization under low Pi stress by positively regulating the expression of ZmPHR1, ZmPHT1;2, and ZmPHO2, which are key Pi transporters in the Pi transport machinery of maize. Overall, enhanced root development and expression of key Pi transporter proteins have been suggested as key nexuses mediating the biological function of ZmARF1 in conferring low-Pi stress tolerance in maize. [ABSTRACT FROM AUTHOR]

Spectral technology is theoretically effective in diagnosing N stress in maize (Zea mays L.), but its application is affected by varietal differences. In this study, the responses to N stress, leaf N spectral diagnostic models and the differences between two maize varieties were analysed. The variety "Jiyu 5817" exhibited a greater response to different N stresses at the 12-leaf stage (V12), while "Zhengdan 958" displayed a greater response in the silking stage (R1). Correlation analysis showed that the spectral bands more sensitive to leaf N content were 548–556 nm and 706–721 nm at the V12 stage in "Jiyu 5817" and 760–1142 nm at the R1 stage in "Zhengdan 958". An N spectral diagnostic model that considers the varietal effect improves the model fit and root mean square error (RMSE) with respect to the model without it by 10.6% and 29.2%, respectively. It was concluded that the V12 stage for "Jiyu 5817" and the R1 stage for "Zhengdan 958" were the best diagnostic stages and were more sensitive to N stress, which can further guide fertilization decision-making in precision fertilization. [ABSTRACT FROM AUTHOR]

SUMMARY: Lateral organ boundaries domain (LBD) proteins are plant‐specific transcription factors. Class‐I LBD genes have been widely demonstrated to play pivotal roles in organ development; however, knowledge on class‐II genes remains limited. Here, we report that ZmLBD5, a class‐II LBD gene, is involved in the regulation of maize (Zea mays) growth and the drought response by affecting gibberellin (GA) and abscisic acid (ABA) synthesis. ZmLBD5 is mainly involved in regulation of the TPS‐KS‐GA2ox gene module, which is comprised of key enzyme‐encoding genes involved in GA and ABA biosynthesis. ABA insufficiency increases stomatal density and aperture in overexpression plants and causes a drought‐sensitive phenotype by promoting water transpiration. Increased GA1 levels promotes seedling growth in overexpression plants. Accordingly, CRISPR/Cas9 knockout lbd5 seedlings are dwarf but drought‐tolerant. Moreover, lbd5 has a higher grain yield under drought stress conditions and shows no penalty in well‐watered conditions compared to the wild type. On the whole, ZmLBD5 is a negative regulator of maize drought tolerance, and it is a potentially useful target for drought resistance breeding. Significance Statement: Maize (Zea mays) ZmLBD5 is mainly associated with abscisic acid (ABA) and gibberellin (GA) synthesis by regulating the TPS‐KS‐GA2ox gene module, which is comprised of key enzyme‐encoding genes involved in GA and ABA biosynthesis. ZmLBD5 negatively regulates drought tolerance by repressing ABA synthesis and promoting stomatal development and opening; however, lbd5 mutants have higher grain yield under drought stress conditions and show no penalty in well‐watered conditions compared to the wild type. [ABSTRACT FROM AUTHOR]

Summary: Root architecture remodelling is critical for forage moisture in water‐limited soil. DEEPER ROOTING 1 (DRO1) in Oryza, Arabidopsis, and Prunus has been reported to improve drought avoidance by promoting roots to grow downward and acquire water from deeper soil. In the present study, we found that ZmDRO1 responded more strongly to abscisic acid (ABA)/drought induction in Zea mays ssp. mexicana, an ancestral species of cultivated maize, than in B73. It was proposed that this is one of the reasons why Zea mays ssp. mexicana has a more noticeable change in the downward direction angle of the root and fewer biomass penalties under water‐deficient conditions. Thus, a robust, synthetic ABA/drought‐inducible promoter was used to control the expression of ZmDRO1B73 in Arabidopsis and cultivated maize for drought‐resistant breeding. Interestingly, ABA‐inducible ZmDRO1 promoted a larger downward root angle and improved grain yield by more than 40% under water‐limited conditions. Collectively, these results revealed that different responses to ABA/drought induction of ZmDRO1 confer different drought avoidance abilities, and we demonstrated the application of ZmDRO1 via an ABA‐inducible strategy to alter the root architecture of modern maize to improve drought adaptation in the field. [ABSTRACT FROM AUTHOR]

Key message: Teosinte improves maize grain yield and broadens the maize germplasm. Seventy-one quantitative trait loci associated with 24 differential traits between maize and teosinte were identified. Maize is a major cereal crop with a narrow germplasm that has limited its production and breeding progress. Teosinte, an ancestor of maize, provides valuable genetic resources for maize breeding. To identify the favorable alien alleles in teosinte and its yield potential for maize breeding, 4 backcrossed maize-teosinte recombinant inbred line (RIL) populations were cultivated under five conditions. A North Carolina mating design II experiment was conducted on inbred lines with B73 and Mo17 pedigree backgrounds to analyze their combining ability. Abundant phenotypic variation on 26 traits of four RIL populations were found, of which barren tip length, kernel height, and test weight showed positive genetic improvement potential. The hybrid FM132 (BD138/MP116) showed a superior grain yield to that of the check, with an average yield gain of 4.86%. Moreover, inbred lines BD138 and MP048 showed a higher general grain yield combining ability than those of their corresponding checks. We screened 4,964,439 high-quality single-nucleotide polymorphisms in the BD (B73/Zea diploperennis) RIL population for bin construction and used 2322 bin markers for genetic map construction and quantitative trait loci (QTL) mapping. Via inclusive composite interval mapping, 71 QTL associated with 24 differential traits were identified. Gene annotation and transcriptional expression suggested that Zm00001eb352570 and Zm00001eb352580, both annotated as ethylene-responsive transcription factors, were key candidate genes that regulate ear height and the ratio of ear to plant height. Our results indicate that teosinte could broaden the narrow maize germplasm, improve yield potential, and provide desirable alleles for maize breeding. [ABSTRACT FROM AUTHOR]

The BRI1-EMS suppressor 1 (BES1)/brassinazole-resistant 1(BZR1) transcription factors play crucial roles in plant growth, development, and stress response. However, little is known about the function of maize's BES1/BZR1s. In this study, the ZmBES1/BZR1-3 and ZmBES1/BZR1-9 genes were cloned from maize's inbred line, B73, and they were functionally evaluated by analyzing their expression pattern, subcellular localization, transcriptional activation activity, as well as their heterologous expression in Arabidopsis, respectively. The results of the qRT-PCR showed that the ZmBES1/BZR1-3 and ZmBES1/BZR1-9 genes were predominantly expressed in the root, and their expression was significantly down-regulated by drought stress. The ZmBES1/BZR1-3 and ZmBES1/BZR1-9 proteins localized in the nucleus but showed no transcriptional activation activity as a monomer. Subsequently, it was found that the heterologous expression of the ZmBES1/BZR1-3 and ZmBES1/BZR1-9 genes in Arabidopsis decreased drought tolerance, respectively. The transgenic lines showed a more serious wilting phenotype, shorter root length, lower fresh weight, and higher relative electrolyte leakage (REL) and malondialdehyde (MDA) content compared to the control under drought stress. The RNA-sequencing data showed that the 70.67% and 93.27% differentially expressed genes (DEGs) were significantly down-regulated in ZmBES1/BZR1-3 and ZmBES1/BZR1-9 transgenic Arabidopsis, respectively. The DEGs of ZmBES1/BZR1-3 gene's expressing lines were mainly associated with oxidative stress response and amino acid metabolic process and enriched in phenylpropanoid biosynthesis and protein processing in the endoplasmic reticulum. But the DEGs of the ZmBES1/BZR1-9 gene's expressing lines were predominantly annotated with water deprivation, extracellular stimuli, and jasmonic acid and enriched in phenylpropanoid biosynthesis and plant hormone signal transduction. Moreover, ZmBES1/BZR1-9 increased stomatal aperture in transgenic Arabidopsis under drought stress. This study indicates that ZmBES1/BZR1-3 and ZmBES1/BZR1-9 negatively regulate drought tolerance via different pathways in transgenic Arabidopsis, and it provides insights into the underlying the function of BES1/BZR1s in crops. [ABSTRACT FROM AUTHOR]

Maize (Zea mays) is an important multi-functional crop. The growth and yield of maize are severely affected by drought stress. Previous studies have shown that microRNAs (miRNAs) in maize play important roles in response to abiotic stress; however, their roles in response to drought stress in maize roots is unclear. In our study, we found 375 miRNAs in the roots of 16 inbred lines. Of the 16 lines, zma-MIR168, zma-MIR156, and zma-MIR166 were highly expressed, whereas zma-MIR399, zma-MIR2218, and zma-MIR2275 exhibited low expression levels. The expression patterns of miRNA in parental lines and their derived RILs are different. Over 50% of miRNAs exhibited a lower expression in recombinant inbred lines than in parents. The expression of 50 miRNAs was significantly altered under water stress (WS) in at least three inbred lines, and the expression of miRNAs in drought-tolerant lines changed markedly. To better understand the reasons for miRNA response to drought, the degree of histone modifications for miRNA genes was estimated. The methylation level of H3K4 and H3K9 in miRNA precursor regions changed more noticeably after WS, but no such phenomenon was seen for DNA methylation and m6A modification. After the prediction of miRNA targets using psRNATarget and psRobot, we used correlation analysis and qRT-PCR to further investigate the relationship between miRNAs and target genes. We found that 87 miRNA–target pairs were significantly negatively correlated. In addition, a weighted gene co-expression network analysis using miRNAs, as well as their predicted targets, was conducted to reveal that miR159, miR394, and miR319 may be related to maize root growth. The results demonstrated that miRNAs might play essential roles in the response to drought stress. [ABSTRACT FROM AUTHOR]

Serine/threonine protein phosphatase 2C (PP2C) dephosphorylates proteins and plays crucial roles in plant growth, development, and stress response. In this study, we characterized a clade B member of maize PP2C family, i.e., ZmPP2C26, that negatively regulated drought tolerance by dephosphorylating ZmMAPK3 and ZmMAPK7 in maize. The ZmPP2C26 gene generated ZmPP2C26L and ZmPP2C26S isoforms through untypical alternative splicing. ZmPP2C26S lost 71 amino acids including an MAPK interaction motif and showed higher phosphatase activity than ZmPP2C26L. ZmPP2C26L directly interacted with, dephosphorylated ZmMAPK3 and ZmMAPK7, and localized in chloroplast and nucleus, but ZmPP2C26S only dephosphorylated ZmMAPK3 and localized in cytosol and nucleus. The expression of ZmPP2C26L and ZmPP2C26 was significantly inhibited by drought stress. Meanwhile, the maize zmpp2c26 mutant exhibited enhancement of drought tolerance with higher root length, root weight, chlorophyll content, and photosynthetic rate compared with wild type. However, overexpression of ZmPP2C26L and ZmPP2C26S significantly decreased drought tolerance in Arabidopsis and rice with lower root length, chlorophyll content, and photosynthetic rate. Phosphoproteomic analysis revealed that the ZmPP2C26 protein also altered phosphorylation level of proteins involved in photosynthesis. This study provides insights into understanding the mechanism of PP2C in response to abiotic stress. [ABSTRACT FROM AUTHOR]

Maximizing grain yields with effective fertilization technologies and minimizing nitrogen losses is essential in agroecosystems. In this research, we conducted a two-year field experiment to explore whether dripline spacing and fertilization rate would affect maize grain yield. Two dripline spacings (i.e., one drip line per row of maize with a row space of 60 cm and one drip line per two rows of maize) and two fertilization rates (i.e., high fertilization level: N, 180 kg ha−1; P2O5, 90 kg ha−1; and K2O, 90 kg ha−1 and low level: N, 139.5 kg ha−1; P2O5, 76.5 kg ha−1; and K2O, 76.5 kg ha−1) were employed in this research. The results showed that maize yield was significantly affected by both dripline spacing and fertilization rate. The maize yield was 10.2% higher in the treatment with one drip line per two rows than that in the treatment with one drip line per row. Maize yield increased by 10.9% at the high fertilization level compared to that at the low fertilization level. The quantity of cumulative ammonia volatilization was reduced by 15.1% with one drip line per two rows compared to that with one drip line per row, whereas it increased by 26.9% at the high fertilization level compared with that at the low fertilization level. These results indicated that one drip line per two rows with a high fertilization rate increased the yield and could reduce the environmental burden, which may be economically beneficial and environmentally sound for maize fertigation for green agricultural development. [ABSTRACT FROM AUTHOR]

Although plant-specific NAC transcription factors play crucial roles in response to abiotic stress, few reports describe the regulation of NAC genes in maize (Zea mays) by the cis -natural antisense transcripts (cis -NATs). In this study, 521 NAC genes from Gramineae were classified, of which 51 NAC genes contained cis -NATs. ZmNAC48 and cis- NAT ZmNAC48 co-localized to the same cell nucleus, and both transcripts responded to drought stress. Arabidopsis plants overexpressing ZmNAC 48 had improved drought tolerance, lower rate of water loss, enhanced stomatal closure, and higher rates of survival. Transient expression in both maize protoplasts and tobacco leaves indicated that cis- NAT ZmNAC48 reduced ZmNAC48 expression. Western blotting and ribosome profiling analyses confirmed that cis -NAT ZmNAC48 lacked protein coding potential. Furthermore, the cis -NAT-derived small-interfering RNAs (nat-siRNAs) generated from the overlapping regions of ZmNAC48 and cis- NAT ZmNAC48 were detected in maize and transgenic Arabidopsis. Cis -NAT ZmNAC48 overexpressing maize showed higher water loss rate, increased stomatal opening, and had more dead leaves. Expression of ZmNAC48 and nat-siRNA was decreased in these plants. Taken together, our study indicates that both ZmNAC48 and cis -NAT ZmNAC48 are involved in plant drought stress responses, and that the double-stranded RNA-dependent mechanism is involved in the interaction between cis -NAT ZmNAC48 and ZmNAC48. Additionally, cis -NAT ZmNAC48 may negatively regulate ZmNAC48 to affect stomatal closure of maize. [ABSTRACT FROM AUTHOR]

The BES1/BZR1 transcription factors regulate the expression of genes responsive to brassinosteroids and play pivotal roles in plant development, but their role in regulating kernel development in maize remains unclear. In this study, we found that ZmBES1/BZR1-5 positively regulates kernel size. Association analysis of candidate genes in 513 diverse maize inbred lines indicated that three SNPs related to ZmBES1/BZR1-5 were significantly associated with kernel width and whilst four SNPs were related to 100-kernel weight. Overexpression of ZmBES1/BZR1-5 in Arabidopsis and rice both significantly increased seed size and weight, and smaller kernels were produced in maize Mu transposon insertion and EMS mutants. The ZmBES1/BZR1-5 protein locates in the nucleus, contains bHLH and BAM domains, and shows no transcriptional activity as a monomer but forms a homodimer through the BAM domain. ChIP-sequencing analysis, and yeast one-hybrid and dual-luciferase assays demonstrated that the protein binds to the promoters of AP2/EREBP genes (Zm00001d010676 and Zm00001d032077) and inhibits their transcription. cDNA library screening showed that ZmBES1/BZR1-5 interacts with casein kinase II subunit β4 (ZmCKIIβ4) and ferredoxin 2 (ZmFdx2) in vitro and in vivo , respectively. Taken together, our study suggests that ZmBES1/BZR1-5 positively regulates kernel size, and provides new insights into understanding the mechanisms of kernel development in maize. [ABSTRACT FROM AUTHOR]

Aluminum (Al) toxicity is the primary limiting factor that affects crop yields in acid soil. However, the genes that contribute to the Al tolerance process in maize are still poorly understood. Previous studies have predicted that ZmAT6 is a novel protein which could be upregulated under Al stress condition. Here, we found that ZmAT6 is expressed in many tissues and organs and can be dramatically induced by Al in both the roots and shoots but particularly in the shoots. The overexpression of ZmAT6 in maize and Arabidopsis plants increased their root growth and reduced the accumulation of Al, suggesting the contribution of ZmAT6 to Al tolerance. Moreover, the ZmAT6 transgenic maize plants had lower contents of malondialdehyde and reactive oxygen species (ROS), but much higher proline content and even lower Evans blue absorption in the roots compared with the wild type. Furthermore, the activity of several enzymes of the antioxidant system, such as peroxidase (POD), superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX), increased in ZmAT6 transgenic maize plants, particularly SOD. Consistently, the expression of ZmSOD in transgenic maize was predominant upregulated by Al stress. Taken together, these findings revealed that ZmAT6 could at least partially confer enhanced tolerance to Al toxicity by scavenging ROS in maize. [ABSTRACT FROM AUTHOR]

Teosinte, an ancestor to modern maize, displays an excellent performance regarding resistance to stress, but its yield potential has rarely been reported. To evaluate the potential contribution of teosinte to maize improvement, two maize–teosinte backcrossed recombination inbred line (RIL) populations and their corresponding test‐cross hybrids were planted for trait assessment. In RN and ZP RIL populations, the average coefficients of variation of 31 agronomic traits were 9.14% (Range, 0.38%‒25.21%) and 6.85% (Range, 0.55%‒27.73%), respectively. The correlation coefficients of 13 common shared traits between RIL populations and test‐cross hybrid populations ranged from 0.10 to 0.60 and from 0.06 to 0.72, respectively. A total of 39 and 3 recombined inbred lines, and 29 and 47 test‐cross hybrids exhibited higher yields than their checks (RP125, Zheng58, CD189 and ZD958) with the BLUP data, respectively. Furthermore, four test‐cross hybrids including RN034/SCML1950, ZP068/Chang7‐2, ZP079/Chang7‐2 and ZP122/Chang7‐2 showed a more stable yield performance, with yield gains of +7.07%, +3.64%, +5.83% and +3.82% over checks, respectively. In conclusion, teosinte could serve as an alien germplasm for maize breeding. [ABSTRACT FROM AUTHOR]

Sweet corn juice is becoming increasingly popular in China. In order to provide valuable health-related information to consumers, the nutritional and physicochemical characteristics of raw and boiled purple sweet corn juices were herein investigated. Sugars, antinutrients, total free phenols, anthocyanins, and antioxidant activity were analyzed by conventional chemical methods. The viscosity and stability of juices were determined by Ubbelohde viscosity meter and centrifugation, respectively. Boiling process could elevate viscosity, stability and sugar content, and reduce antinutrients, total free phenols, anthocyanins, and antioxidant activity in corn juice. In addition, short time boiling efficiently reduced the degradation of anthocyanins during subsequent refrigeration. The content of amino acids, vitamin B1/B2 and E were detected by High Performance Liquid Chromatography. Gas Chromatography Mass Spectrometry was used for the analysis of fatty acids and aroma compounds. Several aroma compounds not previously reported in corn were identified, including 1-heptanol, 2-methyl-2-butenal, (Z)-3-nonen-1-ol, 3-ethyl-2-methyl-1,3-hexadiene, and 2,4-bis(1,1-dimethylethyl)phenol. Interestingly, the boiling process had no apparent effect on the amino acids profile, but it caused a 45.8% loss of fatty acids in the juice by promoting the retention of fatty acids in the corn residue. These results provide detailed information that could be used for increasing consumers' knowledge of sweet corn juice, further development of sweet corn juice by food producers, and maize breeding programs. [ABSTRACT FROM AUTHOR]

Whereas breeders have exploited diversity in maize for yield improvements, there has been limited progress in using beneficial alleles in undomesticated varieties. Characterizing standing variation in this complex genome has been challenging, with only a small fraction of it described to date. Using a population genetics scoring model, we identified 55 million SNPs in 103 lines across pre-domestication and domesticated Zea mays varieties, including a representative from the sister genus Tripsacum. We find that structural variations are pervasive in the Z. mays genome and are enriched at loci associated with important traits. By investigating the drivers of genome size variation, we find that the larger Tripsacum genome can be explained by transposable element abundance rather than an allopolyploid origin. In contrast, intraspecies genome size variation seems to be controlled by chromosomal knob content. There is tremendous overlap in key gene content in maize and Tripsacum, suggesting that adaptations from Tripsacum (for example, perennialism and frost and drought tolerance) can likely be integrated into maize. [ABSTRACT FROM AUTHOR]

Drought often delays developmental events so that plant height and above-ground biomass are reduced, resulting in yield loss due to inadequate photosynthate. In this study, plant height and biomass measured by the Normalized Difference Vegetation Index (NDVI) were used as criteria for drought tolerance. A total of 305 lines representing temperate, tropical and subtropical maize germplasm were genotyped using two single nucleotide polymorphism (SNP) chips each containing 1536 markers, from which 2052 informative SNPs and 386 haplotypes each constructed with two or more SNPs were used for linkage disequilibrium (LD) or association mapping. Single SNP- and haplotype-based LD mapping identified two significant SNPs and three haplotype loci [a total of four quantitative trait loci (QTL)] for plant height under well-watered and water-stressed conditions. For biomass, 32 SNPs and 12 haplotype loci (30 QTL) were identified using NDVIs measured at seven stages under the two water regimes. Some significant SNP and haplotype loci for NDVI were shared by different stages. Comparing significant loci identified by single SNP- and haplotype-based LD mapping, we found that six out of the 14 chromosomal regions defined by haplotype loci each included at least one significant SNP for the same trait. Significant SNP haplotype loci explained much higher phenotypic variation than individual SNPs. Moreover, we found that two significant SNPs (two QTL) and one haplotype locus were shared by plant height and NDVI. The results indicate the power of comparative LD mapping using single SNPs and SNP haplotypes with QTL shared by plant height and biomass as secondary traits for drought tolerance in maize. [ABSTRACT FROM AUTHOR]

The control of flowering is not only important for reproduction, but also plays a key role in the processes of domestication and adaptation. To reveal the genetic architecture for flowering time and photoperiod sensitivity, a comprehensive evaluation of the relevant literature was performed and followed by meta analysis. A total of 25 synthetic consensus quantitative trait loci (QTL) and four hot-spot genomic regions were identified for photoperiod sensitivity including 11 genes related to photoperiod response or flower morphogenesis and development. Besides, a comparative analysis of the QTL for flowering time and photoperiod sensitivity highlighted the regions containing shared and unique QTL for the two traits. Candidate genes associated with maize flowering were identified through integrated analysis of the homologous genes for flowering time in plants and the consensus QTL regions for photoperiod sensitivity in maize ( Zea mays L.). Our results suggest that the combination of literature review, meta-analysis and homologous blast is an efficient approach to identify new candidate genes and create a global view of the genetic architecture for maize photoperiodic flowering. Sequences of candidate genes can be used to develop molecular markers for various models of marker-assisted selection, such as marker-assisted recurrent selection and genomic selection that can contribute significantly to crop environmental adaptation. [ABSTRACT FROM AUTHOR]

Abstract: A total of 550 maize inbred lines collected from global breeding programs were evaluated for drought resistance under both well-watered and water-stressed environments. The evaluation was based on multiple measurements of biomass taken before and after the drought stress was applied using the normalized difference vegetation index (NDVI), along with other selection criteria including anthesis-silking interval, leaf senescence, chlorophyll content, root capacitance, final grain yield, and grain yield components. Kernel weight was the most stable trait under drought stress. Correlations between the primary trait (grain yield) and the secondary traits, except the root capacitance and ASI under water-stressed condition, were all significant. Root capacitance had relatively low heritability and low genetic correlation with other drought resistance criteria, and is not recommended as a drought resistance criterion. Significant reduction of NDVI values measured in the afternoon when the leaves became rolling, compared to those measured in the morning when the leaves were open, provides a reliable index for leaf rolling, which however was not significantly correlated with grain yield. NDVIs measured across different developmental stages were highly correlated with each other and with most of the secondary traits as well as, grain yield, indicating that NDVI can be used as a secondary trait for large-scale drought resistance screening. Regression models built based on non-yield drought criteria and yield components explained about 40% and 95% of the variation for the grain yield, respectively. Some maize lines developed in China for temperate regions showed strong drought resistance comparable to tropical maize lines when tested under tropical condition, indicating that temperate lines with a wide adaptability can be used in drought resistance breeding for both temperate and tropical environments. [Copyright &y& Elsevier]

Plant growth and development are closely related to phosphate (Pi) and auxin. However, data regarding auxin response factors (ARFs) and their response to phosphate in maize are limited. Here, we isolated ZmARF4 in maize and dissected its biological function response to Pi stress. Overexpression of ZmARF4 in Arabidopsis confers tolerance of Pi deficiency with better root morphology than wild-type. Overexpressed ZmARF4 can partially restore the absence of lateral roots in mutant arf7 arf19. The ZmARF4 overexpression promoted Pi remobilization and up-regulated AtRNS1, under Pi limitation while it down-regulated the expression of the anthocyanin biosynthesis genes AtDFR and AtANS. A continuous detection revealed higher activity of promoter in the Pi-tolerant maize P178 line than in the sensitive 9782 line under low-Pi conditions. Meanwhile, GUS activity was specifically detected in new leaves and the stele of roots in transgenic offspring. ZmARF4 was localized to the nucleus and cytoplasm of the mesophyll protoplast and interacted with ZmILL4 and ZmChc5, which mediate lateral root initiation and defense response, respectively. ZmARF4 overexpression also conferred salinity and osmotic stress tolerance in Arabidopsis. Overall, our findings suggest that ZmARF4, a pleiotropic gene, modulates multiple stress signaling pathways, and thus, could be a candidate gene for engineering plants with multiple stress adaptation. [ABSTRACT FROM AUTHOR]

DNA methylation is important for plant growth, development, and stress response. To understand DNA methylation dynamics in maize roots under water stress (WS), we reanalyzed DNA methylation sequencing data to profile DNA methylation and the gene expression landscape of two inbred lines with different drought sensitivities, as well as two of their derived recombination inbred lines (RILs). Combined with genotyping-by-sequencing, we found that the inheritance pattern of DNA methylation between RILs and parental lines was sequence-dependent. Increased DNA methylation levels were observed under WS and the methylome of drought-tolerant inbred lines were much more stable than that of the drought-sensitive inbred lines. Distinctive differentially methylated genes were found among diverse genetic backgrounds, suggesting that inbred lines with different drought sensitivities may have responded to stress in varying ways. Gene body DNA methylation showed a negative correlation with gene expression but a positive correlation with exon splicing events. Furthermore, a positive correlation of a varying extent was observed between small interfering RNA (siRNA) and DNA methylation, which at different genic regions. The response of siRNAs under WS was consistent with the differential DNA methylation. Taken together, our data can be useful in deciphering the roles of DNA methylation in plant drought-tolerance variations and in emphasizing its function in alternative splicing. [ABSTRACT FROM AUTHOR]

Drought stress is a common abiotic factor and restricts plant growth and development. Exploring maize stress-related genes and their regulatory mechanisms is crucial for ensuring agricultural productivity and food security. The BRI1-EMS1 suppressor (BES1)/brassinazole-resistant 1 (BZR1) transcription factors (TFs) play important roles in plant growth, development, and stress response. However, maize ZmBES1/BZR1s are rarely reported. In the present study, the ZmBES1/BZR1-1 gene was cloned from maize B73 and functionally characterized in transgenic Arabidopsis and rice in drought stress response. The ZmBES1/BZR1-1 protein possessed a conserved bHLH domain characterized by BES1/BZR1 TFs, localized in the nucleus, and showed transcription activation activity. The expression of ZmBES1/BZR1-1 exhibited no tissue specificity but drought-inhibitory expression in maize. Under drought stress, overexpression of ZmBES1/BZR1-1 resulted in the enhancement of drought sensitivity of transgenic Arabidopsis and rice with a lower survival rate, reactive oxygen species (ROS) level and relative water content (RWC) and a higher stomatal aperture and relative electrolyte leakage (REL). The RNA-seq results showed that 56 differentially expressed genes (DEGs) were regulated by ZmBES1/BZR1-1 by binding to E-box elements in their promoters. The GO analysis showed that the DEGs were significantly annotated with response to oxidative stress and oxygen level. The study suggests that the ZmBES1/BZR1-1 gene negatively regulates drought stress, which provides insights into further underlying molecular mechanisms in the drought stress response mediated by BZR1/BES1s. • The ZmBES1/BZR1-1 protein localized in the nucleus and showed transcription activation activity. • The expression of ZmBES1/BZR1-1 gene was responsive to drought stress. • Overexpression of ZmBES1/BZR1-1 negatively regulated drought tolerance in transgenic Arabidopsis and rice. [ABSTRACT FROM AUTHOR]

Nitrogen (N) fertilizer application has revolutionized agricultural productivity, but excessive N fertilizer application has resulted in low N use efficiency (NUE) and high N accumulation, increasing the risk of N losses. Here, we hypothesize that the apparent N balance can be used as an indicator to identify the N input for obtaining high yield with a high NUE. Thus, a 12-year field experiment involving seven N treatments (0, 120, 240, 360, 480, 600, and 720 kg N ha–1 per year) in a typical winter wheat-summer maize rotation system in North China was conducted to investigate the response of crop yield and NUE to the N balance under different N application rates and to identify the N input–output framework. The annual yield increased in a linear-platform and NUE decreased with increasing N fertilizer application. The N balance and yield are strongly correlated to predict changes in yield, and a critical N balance of 44.4–64.9 kg N ha–1 per year was recommended for optimal yield with minimal risk of N loss. The N balance and NUE can be presented in the framework of N input–output, and the critical N input estimated from the N balance of 217–252 kg N ha–1 could obtain high productivity with high NUE (74.3–79.6 %). Overall, the apparent N balance could be used as a key indicator for optimizing N input, providing a strong reference for limiting N excess in intensive production areas and evaluating agronomic and environmental performance in N management. The datasets generated during and analyzed during the current study are available from the corresponding author on reasonable request. • Apparent N balance could predict productivity of N output and N use efficiency. • The maximum yield derived N balance upper limit was 64.9 kg N ha−1. • Critical N application rate were determined to be 217–252 kg N ha−1. • The target range for NUE estimated from the N balance was 74.3–79.6 %. [ABSTRACT FROM AUTHOR]