Resistance to Fusarium verticillioides and fumonisin accumulation in maize inbred lines involves an earlier and enhanced expression of lipoxygenase (LOX) genes.

Fusarium verticillioides causes ear rot in maize and contaminates the kernels with the fumonisin myco-toxins. It is known that plant lipoxygenase (LOX)-derived oxylipins regulate defence against pathogensand that the host-pathogen lipid cross-talk influences the pathogenesis. The expression profiles of fif-teen genes of the LOX pathway were studied in kernels of resistant and susceptible maize lines, grownin field condition, at 3, 7 and 14 days post inoculation (dpi) with F. verticillioides. Plant defence responseswere correlated with the pathogen growth, the expression profiles of fungal FUM genes for fumonisinbiosynthesis and fumonisin content in the kernels. The resistant genotype limited fungal growth andfumonisin accumulation between 7 and 14 dpi. Pathogen growth became exponential in the susceptibleline after 7 dpi, in correspondence with massive transcription of FUM genes and fumonisins augmentedexponentially at 14 dpi. LOX pathway genes resulted strongly induced after pathogen inoculation in theresistant line at 3 and 7 dpi, whilst in the susceptible line the induction was reduced or delayed at 14 dpi.In addition, all genes resulted overexpressed before infection in kernels of the resistant genotype alreadyat 3 dpi. The results suggest that resistance in maize may depend on an earlier activation of LOX genesand genes for jasmonic acid biosynthesis

Functional genomic analysis of constitutive and inducible defense responses to Fusarium verticillioides infection in maize genotypes with contrasting ear rot resistance.

Background: Fusarium verticillioides causes ear rot in maize (Zea mays L.) and accumulation of mycotoxins, that affect human and animal health. Currently, chemical and agronomic measures to control Fusarium ear rot are not very effective and selection of more resistant genotypes is a desirable strategy to reduce contaminations. A deeper knowledge of molecular events and genetic basis underlying Fusarium ear rot is necessary to speed up progress in breeding for resistance. Results: A next-generation RNA-sequencing approach was used for the first time to study transcriptional changes associated with F. verticillioides inoculation in resistant CO441 and susceptible CO354 maize genotypes at 72 hours post inoculation. More than 100 million sequence reads were generated for inoculated and uninoculated control plants and analyzed to measure gene expression levels. Comparison of expression levels between inoculated vs. uninoculated and resistant vs. susceptible transcriptomes revealed a total number of 6,951 differentially expressed genes. Differences in basal gene expression were observed in the uninoculated samples. CO441 genotype showed a higher level of expression of genes distributed over all functional classes, in particular those related to secondary metabolism category. After F. verticillioides inoculation, a similar response was observed in both genotypes, although the magnitude of induction was much greater in the resistant genotype. This response included higher activation of genes involved in pathogen perception, signaling and defense, including WRKY transcription factors and jasmonate/ ethylene mediated defense responses. Interestingly, strong differences in expression between the two genotypes were observed in secondary metabolism category: pathways related to shikimate, lignin, flavonoid and terpenoid biosynthesis were strongly represented and induced in the CO441 genotype, indicating that selection to enhance these traits is an additional strategy for improving resistance against F. verticillioides infection. Conclusions: The work demonstrates that the global transcriptional analysis provided an exhaustive view of genes involved in pathogen recognition and signaling, and controlling activities of different TFs, phytohormones and secondary metabolites, that contribute to host resistance against F. verticillioides. This work provides an important source of markers for development of disease resistance maize genotypes andmay have relevance to study other pathosystems involving mycotoxin-producing fungi

Identification of genes, QTLs and metabolites for Fusarium aer rot resistance in maize

Fusarium verticillioides è responsabile della fusariosi della spiga in mais e della contaminazione della granella con micotossine. Sono state individuate le regioni geniche e i geni candidati per la resistenza a Fusarium dal confronto tra una linea di mais resistente (CO441) e una suscettibile (CO354), impiegando tre diversi approcci: analisi QTL, analisi trascrittomica (RNASeq) e analisi metabolomica. 184 famiglie F2:3 (CO441xCO354) sono state valutate in due diversi ambienti nell’anno 2011 e inoculate artificialmente con due diverse tecniche (forchetta e stuzzicadente). E’ stata rilevata una significativa variazione genotipica in risposta all’infezione. Sulla base di una mappa preliminare di linkage molecolare contenente 74 marcatori microsatelliti polimorfici, sono stati determinati 8 QTLs comuni alla resistenza alla fusariosi della spiga e alla riduzione della contaminazione da fumonisine. Sono stati considerati geni candidati per la resistenza i geni differenzialmente espressi, risultanti dall’ RNASeq, in semi di mais CO441 prima e 72 ore dopo l’infezione. I metaboliti putativi correlati alla resistenza sono stati rilevati tramite high resolution LC-MS in entrambe le linee di mais. I geni candidati e i metaboliti mappano in pathway coinvolti nei meccanismi di difesa: fenilalanina, tirosina e triptofano biosintesi, fenilpropanoidi e flavonoidi biosintesi, metabolismo dell’acido linoleico e α-linolenico. Abbondanti trascritti derivano dalla biosintesi dei terpenoidi e dei diterpenoidi. Nei geni candidati verranno ricercati polimorfismi fra le due linee di mais e che andranno ad arricchire la mappa di linkage molecolare.Fusarium verticillioides is responsible for Fusarium ear rot in maize and mycotoxin contamination of grain. Genomic regions and candidate genes for resistance to Fusarium were detected through the comparison of resistant (CO441) and susceptible (CO354) maize lines, by following three different approaches: Quantitative Trait Locus (QTL), transcriptomic (RNASeq) and metabolomic analyses. 184 F2:3 families (CO441xCO354) were evaluated in two different environments in 2011 and artificially infected with two side-needle inoculation methods (pin-bar and toothpick). Significant genotypic variation in response to infection was detected. On the basis of a genetic draft map containing 74 polymorphic SSRs markers, 8 common QTLs for Fusarium ear rot resistance and fumonisin contamination reduction were revealed. Candidate genes for resistance resulted from differentially expressed genes before and 72 hours post infection of CO441 kernels through RNASeq technology. Putative metabolites related to resistance were detected through high resolution LC-MS in both maize lines. Candidate genes and metabolites mapped in pathways involved in defense mechanism: phenylalanine, tyrosine and tryptophan biosynthesis, phenylpropanoid and flavonoid biosynthesis, linoleic and α-linolenic acid metabolism. Abundant genic transcripts derived from terpenoid and diterpenoid biosynthesis. Candidate genes will be screened for polymorphisms between the two maize lines in order to enrich the linkage map

“I know but I can’t explain it”: a starting point for the development of argumentation abilities in prospective primary teacher education

Argumentation is a complex ability both from the cognitive and from the linguistic-communicative point of view and the development of argumentation abilities is a very important part of teaching programs in the Italian school system. Argumentation is also a crucial topic in mathematics education research from kindergarten to university level. This paper considers the topic of argumentation from the perspective of teacher education and presents the first results of a research involving the collaboration between mathematicians and linguists with the common objective of promoting the development of argumentation skills in students attending the university course in Sciences of Primary Education. After introducing the issue of argumentation in language and mathematics education, we recall Toulmin’s model for the analysis of arguments and discuss the specific approaches to argumentation in linguistics and in mathematics education. Then, we present the first data derived from our analysis of prospective primary teachers’ argumentation skills in written and oral presentations. What emerges is that our students tend to describe rather than argue, as testified also by a limited presence of linguistic markers of argumentation; moreover, also when they produce claims, they do not seem aware of the necessity to support their claims with data and warrants. These preliminary data show that both written and oral argumentation abilities need to be developed and trained in the students in Sciences of Primary Education and that Toulmin’s model and its adaptation by Lo Cascio can be an adequate basis for this development

Infection with toxigenic and atoxigenic strains of induces different transcriptional signatures in maize kernels

The application of atoxigenic Aspergillus flavus strains in maize fields has been shown to be an effective strategy for controlling contamination of aflatoxins, potent carcinogens produced by the fungus. This study monitored the expression levels of 18 defense genes against toxigenic and atoxigenic A. flavus strains in developing maize kernels over a time course of 96 h after inoculation. A stronger upregulation of genes encoding pathogenesis-related proteins, oxidative stress-related proteins, transcriptional factors and lipoxygenases were observed in response to the atoxigenic strain. On the other side, this strain showed a significant enhanced growth in the later stages of infection, measured as copy number of the constitutive calmodulin gene. These results suggest that overexpression of maize-defense-associated genes observed in response to the atoxigenic strain could contribute to an aflatoxin reduction. The identification of genes significantly affecting the resistance to A. flavus or aflatoxin accumulation would accelerate the development of resistant cultivars

Defense responses to mycotoxin-producing fungi Fusarium proliferatum, F. subglutinans, and Aspergillus flavus in kernels of susceptible and resistant maize genotypes

Developing kernels of resistant and susceptible maize genotypes were inoculated with Fusarium proliferatum, F. subglutinans, and Aspergillus flavus. Selected defense systems were investigated using real-time reverse transcription-polymerase chain reaction to monitor the expression of pathogenesis-related (PR) genes (PR1, PR5, PRm3, PRm6) and genes protective from oxidative stress (peroxidase, catalase, superoxide dismutase and ascorbate peroxidase) at 72 h postinoculation. The study was also extended to the analysis of the ascorbate-glutathione cycle and catalase, superoxide dismutase, and cytosolic and wall peroxidases enzymes. Furthermore, the hydrogen peroxide and malondialdehyde contents were studied to evaluate the oxidation level. Higher gene expression and enzymatic activities were observed in uninoculated kernels of resistant line, conferring a major readiness to the pathogen attack. Moreover expression values of PR genes remained higher in the resistant line after inoculation, demonstrating a potentiated response to the pathogen invasions. In contrast, reactive oxygen species-scavenging genes were strongly induced in the susceptible line only after pathogen inoculation, although their enzymatic activity was higher in the resistant line. Our data provide an important basis for further investigation of defense gene functions in developing kernels in order to improve resistance to fungal pathogens. Maize genotypes with overexpressed resistance traits could be profitably utilized in breeding programs focused on resistance to pathogens and grain safety

Infection with toxigenic and atoxigenic strains of <i>Aspergillus flavus</i> induces different transcriptional signatures in maize kernels

<p>The application of atoxigenic <i>Aspergillus flavus</i> strains in maize fields has been shown to be an effective strategy for controlling contamination of aflatoxins, potent carcinogens produced by the fungus. This study monitored the expression levels of 18 defense genes against toxigenic and atoxigenic <i>A. flavus</i> strains in developing maize kernels over a time course of 96 h after inoculation. A stronger upregulation of genes encoding pathogenesis-related proteins, oxidative stress-related proteins, transcriptional factors and lipoxygenases were observed in response to the atoxigenic strain. On the other side, this strain showed a significant enhanced growth in the later stages of infection, measured as copy number of the constitutive <i>calmodulin</i> gene. These results suggest that overexpression of maize-defense-associated genes observed in response to the atoxigenic strain could contribute to an aflatoxin reduction. The identification of genes significantly affecting the resistance to <i>A. flavus</i> or aflatoxin accumulation would accelerate the development of resistant cultivars.</p

Molecular Basis of Resistance to Fusarium Ear Rot in Maize

The impact of climate change has been identified as an emerging issue for food security and safety, and the increased incidence of mycotoxin contamination in maize over the last two decades is considered a potential emerging hazard. Disease control by chemical and agronomic approaches is often ineffective and increases the cost of production; for this reason the exploitation of genetic resistance is the most sustainable method for reducing contamination. The review focuses on the significant advances that have been made in the development of transcriptomic, genetic and genomic information for maize, Fusarium verticillioides molds, and their interactions, over recent years. Findings from transcriptomic studies have been used to outline a specific model for the intracellular signaling cascade occurring in maize cells against F. verticillioides infection. Several recognition receptors, such as receptor-like kinases and R genes, are involved in pathogen perception, and trigger down-stream signaling networks mediated by mitogen-associated protein kinases. These signals could be orchestrated primarily by hormones, including salicylic acid, auxin, abscisic acid, ethylene, and jasmonic acid, in association with calcium signaling, targeting multiple transcription factors that in turn promote the down-stream activation of defensive response genes, such as those related to detoxification processes, phenylpropanoid, and oxylipin metabolic pathways. At the genetic and genomic levels, several quantitative trait loci (QTL) and single-nucleotide polymorphism markers for resistance to Fusarium ear rot deriving from QTL mapping and genome-wide association studies are described, indicating the complexity of this polygenic trait. All these findings will contribute to identifying candidate genes for resistance and to applying genomic technologies for selecting resistant maize genotypes and speeding up a strategy of breeding to contrast disease, through plants resistant to mycotoxin-producing pathogens

Mapping candidate genes for Fusarium ear rot resistance

Fusarium ear rot is one of the most important disease of maize, that is of concerns because Fusarium verticillioides produces the mycotoxins fumonisins. Resistance to Fusarium ear rot is polygenic with nearly complete dominance or overdominance of resistance alleles. The availability of molecular markers associated to resistance genes could be a successful strategy to select lines resistant to F. verticillioides. Mapping of quantitative trait loci (QTLs) provides a powerful method to understand the genetic relationships between correlated traits. We attempt to use a genetical-genomics strategy to localize candidate genes for resistance to F. verticillioides on the high density molecular map