Abstract
BackgroundFusarium 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.ResultsA 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.ConclusionsThe 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 and may have relevance to study other pathosystems involving mycotoxin-producing fungi.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-710) contains supplementary material, which is available to authorized users.
Highlights
Fusarium verticillioides causes ear rot in maize (Zea mays L.) and accumulation of mycotoxins, that affect human and animal health
F. verticillioides growth on CO441 and CO354 maize genotypes The two maize inbreds CO441 and CO354, previously classified as resistant and susceptible to F. verticillioides according to their field behavior and growth assay by absolute quantification of the fungal β-tubulin2 (TUB2) transcript through real-time RT-PCR analysis, were used in this study [11,16,17]
The highest transcript copy number was found at 96 hpi in both genotypes, in the resistant line CO441 gene copy number was about twenty-nine times lower compared to the susceptible line CO354 (99.8 ± 16.1 vs. 2,856 ± 250, respectively; Table 1)
Summary
Fusarium verticillioides causes ear rot in maize (Zea mays L.) and accumulation of mycotoxins, that affect human and animal health. 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. F. verticillioides is associated with maize in most stages of this plant’s growth cycle. The fungus is both a parasite and a saprophyte. Disease control by chemical and agronomic approaches is often ineffective and increases the cost of production [6]. For this reason host resistance is the most durable and sustainable method to reduce losses
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