Integrated database for identifying candidate genes for Aspergillus flavus resistance in maize

BACKGROUND: Aspergillus flavus Link:Fr, an opportunistic fungus that produces aflatoxin, is pathogenic to maize and other oilseed crops. Aflatoxin is a potent carcinogen, and its presence markedly reduces the value of grain. Understanding and enhancing host resistance to A. flavus infection and/or subsequent aflatoxin accumulation is generally considered an efficient means of reducing grain losses to aflatoxin. Different proteomic, genomic and genetic studies of maize (Zea mays L.) have generated large data sets with the goal of identifying genes responsible for conferring resistance to A. flavus, or aflatoxin. RESULTS: In order to maximize the usage of different data sets in new studies, including association mapping, we have constructed a relational database with web interface integrating the results of gene expression, proteomic (both gel-based and shotgun), Quantitative Trait Loci (QTL) genetic mapping studies, and sequence data from the literature to facilitate selection of candidate genes for continued investigation. The Corn Fungal Resistance Associated Sequences Database (CFRAS-DB) (http://agbase.msstate.edu/) was created with the main goal of identifying genes important to aflatoxin resistance. CFRAS-DB is implemented using MySQL as the relational database management system running on a Linux server, using an Apache web server, and Perl CGI scripts as the web interface. The database and the associated web-based interface allow researchers to examine many lines of evidence (e.g. microarray, proteomics, QTL studies, SNP data) to assess the potential role of a gene or group of genes in the response of different maize lines to A. flavus infection and subsequent production of aflatoxin by the fungus. CONCLUSIONS: CFRAS-DB provides the first opportunity to integrate data pertaining to the problem of A. flavus and aflatoxin resistance in maize in one resource and to support queries across different datasets. The web-based interface gives researchers different query options for mining the database across different types of experiments. The database is publically available at http://agbase.msstate.edu

Identification of Maize Genes Associated with Host Plant Resistance or Susceptibility to Aspergillus flavus Infection and Aflatoxin Accumulation

infection and aflatoxin accumulation. inoculation were compared in two resistant maize inbred lines (Mp313E and Mp04∶86) in contrast to two susceptible maize inbred lines (Va35 and B73) by microarray analysis. Principal component analysis (PCA) was used to find genes contributing to the larger variances associated with the resistant or susceptible maize inbred lines. The significance levels of gene expression were determined by using SAS and LIMMA programs. Fifty candidate genes were selected and further investigated by quantitative RT-PCR (qRT-PCR) in a time-course study on Mp313E and Va35. Sixteen of the candidate genes were found to be highly expressed in Mp313E and fifteen in Va35. Out of the 31 highly expressed genes, eight were mapped to seven previously identified quantitative trait locus (QTL) regions. A gene encoding glycine-rich RNA binding protein 2 was found to be associated with the host hypersensitivity and susceptibility in Va35. A nuclear pore complex protein YUP85-like gene was found to be involved in the host resistance in Mp313E. infection and aflatoxin accumulation. These findings will be important in identification of DNA markers for breeding maize lines resistant to aflatoxin accumulation

POTENCIES OF THE RESISTANT MAIZE GENOTYPES AGAINST BIOTIC STRESSES AND UNDERSTANDING THEIR STRATEGIES

Maize is an important food crop in most parts of the world including the United States. The plants growing in the field are constantly challenged with various biotic stresses like insect herbivores and fungal pathogens. The physical wounds produced on the growing crops by the insects render the plants more vulnerable to the fungal pathogens. Hence developing both insect and fungal resistant maize varieties is crucial to benefit more from the harvest. Several studies have been in advance in this direction and as a consequence insect, in particular lepidopteran larve resistant maize genotype Mp708 and Aspergillus flavus resistant genotype Mp313E were developed. This study particularly focuses on understanding the functional involvement of the major phytohormones in the signal transduction and expression of the unique defense protein, Maize insect resistance 1-cysteine protease (Mir1-CP) shown to accumulate in response to herbivory by lepidopteran larvae, Spodoptera frugiperda (Fall armyworm, FAW) as a defense mechanism. Using a pharmacological approach involving exogenous hormone and hormone inhibitor treatments and analyzing the expression and accumulation of Mir1-CP protein and mir1 transcript by immunoblot and qRT-PCR analysis respectively, both JA and ET were found to be involved in mediating Mir1-CP accumulation with JA acting upstream of ET. Results also indicate that Mir1-CP accumulation involves both transcriptional and post-transcriptional (or post-translational) regulations. A different part of the study involved in understanding and evaluating the performance of Aspergillus flavus on the resistant and susceptible maize genotypes during infection. As of part of this study I also analyzed and compared the defense response offered by the resistant maize genotype, Mp313E and the susceptible genotype, Va35 by looking at the expression levels of the various defense related genes. The potency of the resistant maize genotype in sustaining the fungal infection in the field was of particular focus. Resistant maize genotype Mp313E was found to potentially oppose A.flavus proliferation and colonization and also delay aflatoxin biosynthesis unlike Va35. The up regulation of the maize defense genes during the early time points of infection, in Mp313E, indicate the potential role of these genes in conferring resistance against fungal pathogens