Analysis of global gene expression profiles in tobacco roots under drought stress

Tobacco (Nicotiana tabacum L.) is an economically important and relatively drought-tolerant crop grown around the world. However, the molecular regulatory mechanisms involved in tobacco root development in response to drought stress are not wellknown. To gain insight into the transcriptome dynamics associated with drought resistance, genome-wide gene expression profiling of roots from a tobacco cultivar (Honghua Dajinyuan, a major flue-cured tobacco cultivar in Southwest China) under 20% PEG6000 treatment for 0, 6 h and 48 h were conducted using Solexa sequencing (Illumina Inc., San Diego, CA, USA). Over five million tags were generated from tobacco roots, including 229,344, 221,248 and 242,065 clean tags in three libraries, respectively. The most differentially expressed tags, with either log2FC > 2.0 for up-regulated genes or log2FC < -2.0 for down regulated genes (p < 0.001), were analyzed further. In comparison to the control, 1476 up-regulated and 1574 down-regulated differentially expressed genes (DEGs) were identified, except for unknown transcripts, which were grouped into 43 functional categories involved in seven significant pathways. The most enriched categories were those that were populated by transcripts involved in metabolism, signal transduction and cellular transport. Many genes and/or biological pathways were found to be common among the three libraries, for example, genes participating in transport, stress response, auxin transport and signaling, etc. Next, the expression patterns of 12 genes were assessed with quantitative real-time PCR, the results of which agreed with the Solexa analysis. In conclusion, we revealed complex changes in the transcriptome during tobacco root development related to drought resistance, and provided a comprehensive set of data that is essential to understanding the molecular regulatory mechanisms involved. These data may prove valuable in future studies of the molecular mechanisms regulating root development in response to drought stress in tobacco and other plants.

The dynamics of DNA methylation in maize roots under Pb stress

Plants adapt to adverse conditions through a series of physiological, cellular, and molecular processes, culminating in stress tolerance. However, little is known about the associated regulatory mechanisms at the epigenetic level in maize under lead (Pb) stress. Therefore, in this study, we aimed to compare DNA methylation profiles during the dynamic development of maize roots following Pb treatment to identify candidate genes involved in the response to Pb stress. Methylated DNA immunoprecipitation-sequencing (MeDIP-seq) was used to investigate the genome-wide DNA methylation patterns in maize roots under normal condition (A1) and 3 mM Pb(NO₃)₂ stress for 12 h (K2), 24 h (K3) and 48 h (K4). The results showed that the average methylation density was the highest in CpG islands (CGIs), followed by the intergenic regions. Within the gene body, the methylation density of the introns was higher than those of the UTRs and exons. In total, 3857 methylated genes were found in 4 tested samples, including 1805 differentially methylated genes for K2 versus A1, 1508 for K3 versus A1, and 1660 for K4 versus A1. Further analysis showed that 140 genes exhibited altered DNA methylation in all three comparisons, including some well-known stress-responsive transcription factors and proteins, such as MYB, AP2/ERF, bZIP, serine-threonine/tyrosine-proteins, pentatricopeptide repeat proteins, RING zinc finger proteins, F-box proteins, leucine-rich repeat proteins and tetratricopeptide repeat proteins. This study revealed the genome-scale DNA methylation patterns of maize roots in response to Pb exposure and identified candidate genes that potentially regulate root dynamic development under Pb stress at the methylation level.

[Mapping of QTLs controlling Pb(2+) content in maize kernels under Pb(2+)stress]

Lead (Pb(2+)) is one of the most abundant heavy-metal elements in the environment. Pb(2+) pollution has become increasingly serious in maize planting areas, especially in the southwest of China, which even threatens food security. In the present study, a RILpopulation derived from 178 (an inbred line with low accumulation of Pb(2+) in the kernels) and 9782 (a Pb(2+)-hyperaccumulator in the kernels) was used for QTL mapping. A molecular genetic map with the length of 1499.85 cM and an average inter-marker distance of 9.07 cM was constructed with 165 pairs of SSR markers. QTLs controlling Pb(2+) content in maize kernels were then analyzed to provide the basis for breeding elite maize varieties with low Pb(2+)in the kernels. Two QTLs, qPC1 and qPC4, related to Pb(2+) content in maize kernels were identified on chromosome 1 and 4, respectively. qPC1 was located between markers umc1661 and phi002, accounting for 11.13% of phenotypic variance with an additive effect value of 0.062. While qPC4 was located between markers umc1117 and nc005, explaining 5.55% of the phenotypic variance with an additive effect value of -0.044. However, there was no significant correlation observed between Pb(2+) content in the kernels and any of yield-related traits including ear length, ear diameter, kernel row number and weight of per-hundred kernels, indicating that yield-related traits would not be changed in the process of low-Pb(2+)maize breeding. This suggested that the Pb(2+)content in maize kernel under Pb(2+)stress was an independent genetic trait.

Heterosis in early maize ear inflorescence development: a genome-wide transcription analysis for two maize inbred lines and their hybrid

Heterosis, or hybrid vigor, contributes to superior agronomic performance of hybrids compared to their inbred parents. Despite its importance, little is known about the genetic and molecular basis of heterosis. Early maize ear inflorescences formation affects grain yield, and are thus an excellent model for molecular mechanisms involved in heterosis. To determine the parental contributions and their regulation during maize ear-development-genesis, we analyzed genome-wide digital gene expression profiles in two maize elite inbred lines (B73 and Mo17) and their F₁ hybrid using deep sequencing technology. Our analysis revealed 17,128 genes expressed in these three genotypes and 22,789 genes expressed collectively in the present study. Approximately 38% of the genes were differentially expressed in early maize ear inflorescences from heterotic cross, including many transcription factor genes and some presence/absence variations (PAVs) genes, and exhibited multiple modes of gene action. These different genes showing differential expression patterns were mainly enriched in five cellular component categories (organelle, cell, cell part, organelle part and macromolecular complex), five molecular function categories (structural molecule activity, binding, transporter activity, nucleic acid binding transcription factor activity and catalytic activity), and eight biological process categories (cellular process, metabolic process, biological regulation, regulation of biological process, establishment of localization, cellular component organization or biogenesis, response to stimulus and localization). Additionally, a significant number of genes were expressed in only one inbred line or absent in both inbred lines. Comparison of the differences of modes of gene action between previous studies and the present study revealed only a small number of different genes had the same modes of gene action in both maize seedlings and ear inflorescences. This might be an indication that in different tissues or developmental stages, different global expression patterns prevail, which might nevertheless be related to heterosis. Our results support the hypotheses that multiple molecular mechanisms (dominance and overdominance modes) contribute to heterosis.

Genome-wide analysis of water-stress-responsive microRNA expression profile in tobacco roots

MicroRNAs (miRNAs) play a pivotal role in post-transcriptional regulation of gene expression in plants. In this study, we investigate miRNAs in an agronomically important common tobacco in China, named Honghua Dajinyuan (a drought-tolerant cultivar). Here, we report a comprehensive analysis of miRNA expression profiles in mock-treat grown (CK) and 20 % polyethylene glycol-grown (PEG-grown) tobacco roots using a high-throughput sequencing approach. A total of 656 unique miRNAs representing 53 miRNA families were identified in the two libraries, of which 286 unique miRNAs representing 162 microRNAs were differentially expressed. In addition, nine differentially expressed microRNAs selected from different expressed miRNA family with high abundance were subjected to further analysis and validated by quantitative real-time PCR (Q-PCR). In addition, the expression pattern of these identified candidate conserved miRNA and target genes of three identified miRNA (nta-miR172b, nta-miR156i, and nta-miR160a) were also validated by Q-PCR. Gene ontology (GO) enrichment analysis suggests that the putative target genes of these differentially expressed miRNAs are involved in metabolic process and response to stimulus. In particular, 25 target genes are involved in regulating plant hormone signal transduction and metabolism, indicating that these association microRNAs may play important regulatory roles in responding to PEG resistance. Moreover, this study adds a significant number of novel miRNAs to the tobacco miRNome.

A luciferase-based method for assay of 5'-adenylylsulfate reductase

A luciferase-based method was developed for measurement of 5'-adenylylsulfate (APS) reductase (APR), an enzyme of the reductive sulfate assimilation pathway in prokaryotes and plants. APR catalyzes the two-electron reduction of APS and forms sulfite and adenosine 5'-monophospahate (AMP). The luciferase-based assay measures AMP production using an enzyme-coupled system that generates luminescence. The method is shown to provide an accurate measurement of APR kinetic properties and can be used for both endpoint and continuous assays. APR activity can be measured from pure enzyme preparations as well as from crude protein extracts of tissues. In addition, the assay is ideally suited to high-throughput sample analysis of APR activity in a microtiter dish format. The method adds new capability to the study of the biochemistry and physiology of APR.

Validation of potential reference genes for qPCR in maize across abiotic stresses, hormone treatments, and tissue types

The reverse transcription quantitative polymerase chain reaction (RT-qPCR) is a powerful and widely used technique for the measurement of gene expression. Reference genes, which serve as endogenous controls ensure that the results are accurate and reproducible, are vital for data normalization. To bolster the literature on reference gene selection in maize, ten candidate reference genes, including eight traditionally used internal control genes and two potential candidate genes from our microarray datasets, were evaluated for expression level in maize across abiotic stresses (cold, heat, salinity, and PEG), phytohormone treatments (abscisic acid, salicylic acid, jasmonic acid, ethylene, and gibberellins), and different tissue types. Three analytical software packages, geNorm, NormFinder, and Bestkeeper, were used to assess the stability of reference gene expression. The results revealed that elongation factor 1 alpha (EF1α), tubulin beta (β-TUB), cyclophilin (CYP), and eukaryotic initiation factor 4A (EIF4A) were the most reliable reference genes for overall gene expression normalization in maize, while GRP (Glycine-rich RNA-binding protein), GLU1(beta-glucosidase), and UBQ9 (ubiquitin 9) were the least stable and most unsuitable genes. In addition, the suitability of EF1α, β-TUB, and their combination as reference genes was confirmed by validating the expression of WRKY50 in various samples. The current study indicates the appropriate reference genes for the urgent requirement of gene expression normalization in maize across certain abiotic stresses, hormones, and tissue types.

Identification of candidate genes for drought tolerance by whole-genome resequencing in maize

BACKGROUND

Drought stress is one of the major limiting factors for maize production. With the availability of maize B73 reference genome and whole-genome resequencing of 15 maize inbreds, common variants (CV) and clustering analyses were applied to identify non-synonymous SNPs (nsSNPs) and corresponding candidate genes for drought tolerance.

RESULTS

A total of 524 nsSNPs that were associated with 271 candidate genes involved in plant hormone regulation, carbohydrate and sugar metabolism, signaling molecules regulation, redox reaction and acclimation of photosynthesis to environment were detected by CV and cluster analyses. Most of the nsSNPs identified were clustered in bin 1.07 region that harbored six previously reported QTL with relatively high phenotypic variation explained for drought tolerance. Genes Ontology (GO) analysis of candidate genes revealed that there were 35 GO terms related to biotic stimulus and membrane-bounded organelle, showing significant differences between the candidate genes and the reference B73 background. Changes of expression level in these candidate genes for drought tolerance were detected using RNA sequencing for fertilized ovary, basal leaf meristem tissue and roots collected under drought stressed and well-watered conditions. The results indicated that 70% of candidate genes showed significantly expression changes under two water treatments and our strategies for mining candidate genes are feasible and relatively efficient.

CONCLUSIONS

Our results successfully revealed candidate nsSNPs and associated genes for drought tolerance by comparative sequence analysis of 16 maize inbred lines. Both methods we applied were proved to be efficient for identifying candidate genes for complex traits through the next-generation sequencing technologies (NGS). These selected genes will not only facilitate understanding of genetic basis of drought stress response, but also accelerate genetic improvement through marker-assisted selection in maize.

Genome expression profile analysis of the maize sheath in response to inoculation to R. solani

Currently, the molecular regulation mechanisms of disease-resistant involved in maize leaf sheaths infected by banded leaf and sheath blight (BLSB) are poorly known. To gain insight into the transcriptome dynamics that are associated with their disease-resistant, genome-wide gene expression profiling was conducted by Solexa sequencing. More than four million tags were generated from sheath tissues without any leaf or development leaf, including 193,222 and 204,824 clean tags in the two libraries, respectively. Of these, 82,864 (55.4 %) and 91,678 (51.5 %) tags were matched to the reference genes. The most differentially expressed tags with log2 ratio >2 or <-2 (P < 0.001) were further analyzed, representing 1,476 up-regulated and 1,754 down-regulated genes, except for unknown transcripts, which were classified into 11 functional categories. The most enriched categories were those of metabolism, signal transduction and cellular transport. Next, the expression patterns of 12 genes were assessed by quantitative real-time PCR, and it is showed the results were general agreement with the Solexa analysis, although the degree of change was lower in amplitude. In conclusion, we first reveal the complex changes in the transcriptome during the early development of maize sheath infected by BLSB and provide a comprehensive set of data that are essential for understanding its molecular regulation mechanism.

Identification of miRNAs and their target genes in developing maize ears by combined small RNA and degradome sequencing

BACKGROUND

In plants, microRNAs (miRNAs) are endogenous ~22 nt RNAs that play important regulatory roles in many aspects of plant biology, including metabolism, hormone response, epigenetic control of transposable elements, and stress response. Extensive studies of miRNAs have been performed in model plants such as rice and Arabidopsis thaliana. In maize, most miRNAs and their target genes were analyzed and identified by clearly different treatments, such as response to low nitrate, salt and drought stress. However, little is known about miRNAs involved in maize ear development. The objective of this study is to identify conserved and novel miRNAs and their target genes by combined small RNA and degradome sequencing at four inflorescence developmental stages.

RESULTS

We used deep-sequencing, miRNA microarray assays and computational methods to identify, profile, and describe conserved and non-conserved miRNAs at four ear developmental stages, which resulted in identification of 22 conserved and 21-maize-specific miRNA families together with their corresponding miRNA*. Comparison of miRNA expression in these developmental stages revealed 18 differentially expressed miRNA families. Finally, a total of 141 genes (251 transcripts) targeted by 102 small RNAs including 98 miRNAs and 4 ta-siRNAs were identified by genomic-scale high-throughput sequencing of miRNA cleaved mRNAs. Moreover, the differentially expressed miRNAs-mediated pathways that regulate the development of ears were discussed.

CONCLUSIONS

This study confirmed 22 conserved miRNA families and discovered 26 novel miRNAs in maize. Moreover, we identified 141 target genes of known and new miRNAs and ta-siRNAs. Of these, 72 genes (117 transcripts) targeted by 62 differentially expressed miRNAs may attribute to the development of maize ears. Identification and characterization of these important classes of regulatory genes in maize may improve our understanding of molecular mechanisms controlling ear development.

Long-term self-renewal of human pluripotent stem cells on peptide-decorated poly(OEGMA-co-HEMA) brushes under fully defined conditions

Realization of the full potential of human induced pluripotent stem cells (hiPSC) in clinical applications requires the development of well-defined culture conditions for their long-term growth and directed differentiation. This paper describes a novel fully defined synthetic peptide-decorated substrate that supports self-renewal of hiPSC in commercially available xeno-free, chemically defined medium. The Au surface was deposited by a poly(OEGMA-co-HEMA) film, using the surface-initiated polymerization method (SIP) with the further step of carboxylation. The hiPSC generated from umbilical cord mesenchymal cells were successfully cultured for 10 passages on the peptide-tethered poly(OEGMA-co-HEMA) brushes for the first time. Cells maintained their characteristic morphology, proliferation and expressed high levels of markers of pluripotency, similar to the cells cultured on Matrigel™. Moreover, the cell adhesion could be tuned by the pattern and peptide concentration on the substrate. This well-defined, xeno-free and safe substrate, which supports long-term proliferation and self-renewal of hiPSC, will not only help to accelerate the translational perspectives of hiPSC, but also provide a platform to elucidate the underlying molecular mechanisms that regulate stem cell proliferation and differentiation via SIP technology.

Combined small RNA and degradome sequencing reveals microRNA regulation during immature maize embryo dedifferentiation

Genetic transformation of maize is highly dependent on the development of embryonic calli from the dedifferentiated immature embryo. To better understand the regulatory mechanism of immature embryo dedifferentiation, we generated four small RNA and degradome libraries from samples representing the major stages of dedifferentiation. More than 186 million raw reads of small RNA and degradome sequence data were generated. We detected 102 known miRNAs belonging to 23 miRNA families. In total, we identified 51, 70 and 63 differentially expressed miRNAs (DEMs) in the stage I, II, III samples, respectively, compared to the control. However, only 6 miRNAs were continually up-regulated by more than fivefold throughout the process of dedifferentiation. A total of 87 genes were identified as the targets of 21 DEM families. This group of targets was enriched in members of four significant pathways including plant hormone signal transduction, antigen processing and presentation, ECM-receptor interaction, and alpha-linolenic acid metabolism. The hormone signal transduction pathway appeared to be particularly significant, involving 21 of the targets. While the targets of the most significant DEMs have been proved to play essential roles in cell dedifferentiation. Our results provide important information regarding the regulatory networks that control immature embryo dedifferentiation in maize.

Stabilization by hydrophobic protection as a molecular mechanism for organic carbon sequestration in maize-amended rice paddy soils

The hydrophobic components of soil organic matter (SOM) are reckoned to play an important role in the stabilization of soil organic carbon (SOC). The contribution of hydrophobic substances to SOC sequestration was evaluated in four different paddy soils in the South of China, following a 6-month incubation experiment with maize straw amendments. Soil samples included: a well developed paddy soil (TP) derived from clayey lacustrine deposits in the Tai Lake plain of Jiangsu; an acid clayey paddy soil (RP) derived from red earth in the rolling red soil area of Jiangxi; a weakly developed neutral paddy soil (PP) formed on Jurassic purple shale from Chongq; and a calcic Fluvisol (MS) derived from riverine sediments from a wetland along the Yangtze valley of Anhui, China. The SOC molecular composition after 30 and 180 days of incubation, was determined by off-line thermochemolysis followed by gas chromatography-mass spectrometry analysis. Lignin, lipids and carbohydrates were the predominant thermochemolysis products released from the treated soils. A selective preservation of hydrophobic OM, including lignin and lipids, was shown in maize amended soils with prolonged incubation. The decomposition of lignin and lipids was significantly slower in the TP and RP soils characterized by a larger content of extractable iron oxyhydrates (Fed) and lower pH. The overall increase in hydrophobic substances in maize incubated samples was correlated, positively, with total content of clay and Fed, and, negatively, with soil pH. Moreover, yields of both lignin and lipid components showed a significant relationship with SOC increase after incubation. These findings showed that the larger the lipid and lignin content of SOM, the greater was the stability of SOC, thereby suggesting that OM hydrophobic components may have an essential role in controlling the processes of OC sequestration in paddy soils of South China.

Facile preparation of high-quality Pt/reduced graphene oxide nanoscrolls for methanol oxidation

A simple and novel approach for the preparation of a Pt/reduced graphene oxide nanoscroll (Pt/RGOS) nanocatalyst is reported for the first time. The Pt/reduced graphene oxide (Pt/RGO) was fabricated by the co-reduction of GO and Pt salt using ethylene glycol under microwave irradiation, then the Pt/RGOSs were obtained by oxygen implosion in situ rolling up of the Pt/RGO using catalytic decomposition of Pt towards H2O2 under ultrasonication. Transmission electron microscopy shows that the Pt nanoparticles are uniformly dispersed on the reduced graphene oxide nanoscrolls with tubular structure, open edges and ends, and tubular diameter ranging from 10 to 100 nm. X-ray diffraction indicates that the crystal structure and diffraction intensity of the platinum practically remains unchanged, and the RGO has not been oxidized before or after rolling. Raman spectroscopy reveals that the Pt/RGOSs have a higher D/G ratio (1.2) than Pt/RGO (1.1). BET (Brunauer, Emmett and Teller) results exhibit that the Pt/RGOSs possess higher specific surface area and broader pore size range (188 m(2) g(-1), 25-45 nm) than Pt/RGO (122 m(2) g(-1), 30-38 nm). Additionally, the electrocatalytic performance of the Pt/RGOSs for methanol oxidation was evaluated, and the results show that the Pt/RGOSs possess significantly higher electrocatalytic activity and stability than Pt/RGO.

Genome expression profile analysis reveals important transcripts in maize roots responding to the stress of heavy metal Pb

Lead (Pb) has become one of the most abundant heavy metal pollutants of the environment. With its large biomass, maize could be an important object for studying the phytoremediation of Pb-contaminated soil. In our previous research, we screened 19 inbred lines of maize for Pb concentration, and line 178 was identified to be a hyperaccumulator for Pb in both the roots and aboveground parts. To identify important genes and metabolic pathways related to Pb accumulation and tolerance, line 178 was underwent genome expression profile under Pb stress and a control (CK). A total of approximately 11 million cDNA tags were sequenced and 4 665 539 and 4 936 038 clean tags were obtained from the libraries of the test and CK, respectively. In comparison to CK, 2379 and 1832 genes were identified up- or downregulated, respectively, more than fivefolds under Pb stress. Interestingly, all the genes were related to cellular processes and signaling, information storage and processing or metabolism functions. Particularly, the genes involved in posttranslational modification, protein turnover and chaperones; signal transduction, carbohydrate transport and metabolism; and lipid transport and metabolism significantly changed under the treatment. In addition, seven pathways including ribosome, photosynthesis, and carbon fixation were affected significantly, with 118, 12, 34, 21, 18, 72 and 43 differentially expressed genes involved. The significant upregulation of the ribosome pathway may reveal an important secret for Pb tolerance of line 178. And the sharp increase of laccase transcripts and metal ion transporters were suggested to account in part for Pb hyperaccumulation in the line.

Preparation and characterization of EDTAD-modified magnetic-Fe3O4 chitosan composite: application of comparative adsorption of dye wastewater with magnetic chitosan

Ethylenediaminetetraacetic dianhydride (EDTAD)-modified magnetic-Fe3O4 chitosan (EMC), prepared using the cross-link agent glutaraldehyde and chemicals Fe3O4, chitosan, and EDTAD, was used to compare the adsorption of methylene blue (MB) with magnetic chitosan (MC). The composite structure was confirmed by multiple characterization techniques, including scanning electron microscopy (SEM), X-ray powder diffraction, Fourier transform infrared spectroscopy (FTIR), and potentiometric titration methods. The characterization results suggest that Fe3O4 particles successfully bound on the surface of chitosan, and the EDTAD thoroughly modified the MC. Furthermore, EMC had more amino, carboxyl, and hydroxy groups than typical MC. Adsorption conditions, such as pH values, initial concentrations of MB, reaction temperature, and contact time were systematically examined. In comparison, the maximum adsorption capacity of EMC was approximately twice as much as that of MC. The recovery efficiency for EMC was >80% using 0.1 M HCl as an eluent solution. Therefore, the results reported herein indicate that EMC is very attractive and imply a practical application for dye wastewater treatment.

The genetic architecture of flowering time and photoperiod sensitivity in maize as revealed by QTL review and meta analysis

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.

Development of a difenoconazole/propiconazole microemulsion and its antifungal activities against Rhizoctonia solani AG1-IA

According to its physical and chemical properties, the composition of difenoconazole/propiconazole microemulsion was as follows: xylene as solvent, emulsifier HSH as surfactant and methanol as cosurfactant. The optimal formulation of difenoconazole/propiconazole microemulsion was oil/SAA/water = 1/2/5 (w/w), in which the SAA consisted of emulsifier HSH and methanol with ratio of 3/2 (w/w). The cloud point of difenoconazole/propiconazole microemulsion was 70 degrees C and its effective ingredient content was 2.5% measured by High Performance Liquid Chromatography (HPLC). Its heat storage stability was studied according to the standards. The decomposition rates of the difenoconazole/propiconazole microemulsion were merely 2.45%, 2.63% respectively and met the Food and Agriculture Organization (FAO) standards of pesticide microemulsion. Investigated by Transmission Electron Microscopy (TEM) the particle size of difenoconazole/propiconazole microemulsion was 90-140 nm and its antifungal activities against Rhizoctonia solani AG1-IA were tested and compared with that of Meiyu. We found that the inhibition rates in the difenoconazole/propiconazole microemulsion treatment group were significantly higher than that of the emulsion group with the same content of effective ingredients and the study also revealed that its inhibiting ability on the formation and germination of sclerotia was significant.

Cloning and characterization of miRNAs from maize seedling roots under low phosphorus stress

MicroRNAs (miRNAs) are a class of small, non-coding regulatory RNAs that regulate gene expression by guiding target mRNA cleavage or translational inhibition in plants and animals. In this study, a small RNA library was constructed to identify conserved miRNAs as well as novel miRNAs in maize seedling roots under low level phosphorus stress. Twelve miRNAs were identified by high throughput sequencing of the library and subsequent analysis, two belong to conserved miRNA families (miRNA399b and miRNA156), and the remaining ten are novel and one of latter is conserved in gramineous species. Based on sequence homology, we predicted 125 potential target genes of these miRNAs and then expression patterns of 7 miRNAs were validated by semi-RT-PCR analysis. MiRNA399b, Zma-miR3, and their target genes (Zmpt1 and Zmpt2) were analyzed by real-time PCR. It is shown that both miRNA399b and Zma-miR3 are induced by low phosphorus stress and regulated by their target genes (Zmpt1 and Zmpt2). Moreover, Zma-miR3, regulated by two maize inorganic phosphate transporters as a newly identified miRNAs, would likely be directly involved in phosphate homeostasis, so was miRNA399b in Arabidopsis and rice. These results indicate that both conserved and maize-specific miRNAs play important roles in stress responses and other physiological processes correlated with phosphate starvation, regulated by their target genes. Identification of these differentially expressed miRNAs will facilitate us to uncover the molecular mechanisms underlying the progression of maize seedling roots development under low level phosphorus stress.

Genome expression profile analysis of the immature maize embryo during dedifferentiation

Maize is one of the most important cereal crops worldwide and one of the primary targets of genetic manipulation, which provides an excellent way to promote its production. However, the obvious difference of the dedifferentiation frequency of immature maize embryo among various genotypes indicates that its genetic transformation is dependence on genotype and immature embryo-derived undifferentiated cells. To identify important genes and metabolic pathways involved in forming of embryo-derived embryonic calli, in this study, DGE (differential gene expression) analysis was performed on stages I, II, and III of maize inbred line 18-599R and corresponding control during the process of immature embryo dedifferentiation. A total of ∼21 million cDNA tags were sequenced, and 4,849,453, 5,076,030, 4,931,339, and 5,130,573 clean tags were obtained in the libraries of the samples and the control, respectively. In comparison with the control, 251, 324 and 313 differentially expressed genes (DEGs) were identified in the three stages with more than five folds, respectively. Interestingly, it is revealed that all the DEGs are related to metabolism, cellular process, and signaling and information storage and processing functions. Particularly, the genes involved in amino acid and carbohydrate transport and metabolism, cell wall/membrane/envelope biogenesis and signal transduction mechanism have been significantly changed during the dedifferentiation. To our best knowledge, this study is the first genome-wide effort to investigate the transcriptional changes in dedifferentiation immature maize embryos and the identified DEGs can serve as a basis for further functional characterization.

Microbial degradation of microcystin-LR by Ralstonia solanacearum

A bacterial strain was isolated from Lake Dianchi (China) and its degradability and degradative pathways of the cyanobacterial toxin microcystin-LR (MC-LR) were studied. On the basis of morphological, physiological and biochemical tests, the strain was identified as Ralstonia solanacearum. The acute oral toxicity tests showed that Ralstonia solanacearum belongs to a non-toxic class. This bacterium degraded MC-LR at the rate of 9.4 mg/L per day, which was higher than those of the other bacterial strains reported in the literature. As for the degradative pathways, the results showed that the Adda-Arg peptide bond of MC-LR was initially hydrolysed by Ralstonia solanacearum to form a linear molecule as an intermediate. The intermediate product subsequently underwent a cyclisation reaction via dehydration to form a final product with a small peptide ring at one end of the molecule. These biodegradative pathways were different from those reported with other bacterial strains, suggesting that MC-LR may undergo different transformations, and different products were formed due to different compositions of bacteria present in natural lakes and reservoirs. These results suggest that there is a significant potential for Ralstonia solanacearum as a degrader for MC-LR removal from wastewater.