TRANSCRIPTOMIC, GENOMIC AND METABOLOMIC ANALYSIS OF THE PATHOSYSTEM MAIZE-FUSARIUM VERTICILLIOIDES.

Fusarium ear rot is caused by Fusarium verticillioides. Ear infection causes yield loss and the accumulation of fumonisins, frequently found in symptomless kernels. We investigated global gene expression in maize ears at several time points after infection with Fusarium verticillioides. In kernels at 48 h post infection with a fumonisin-producing strain, about 800 differentially expressed sequences were identified and nearly 10% assigned to the category cell rescue, defence and virulence. The expression analysis was extended to early (12, 24 h) and late (72, 96 h) phases after infection. During the very early stages of infection a small proportion of the host transcripts was induced and none of them was involved in defence processes. The highest number of differentially expressed genes was attained at 48 h after infection. The number decreased to 140 and 98 genes at 72 and 96 h following infection, respectively. When resistant and susceptible maize genotypes were compared, in the resistant lines the expression of defence genes were detected before infection, indicative of a basal defence response against the fungus. In the susceptible genotypes defence genes were induced after pathogen infection. The basal defence response was also active against several fungal species invading maize kernels. To clarify the molecular processes undergoing in maize upon infection, the RNA-Seq technology has been applied to characterize the expression profile of resistant and susceptible genotypes after F. verticillioides infection. The identification of differentially expressed plant genes that interact with fungus will produce useful tools for the identification of candidate genes, the development of molecular markers and their use for selection of resistant maize genotypes by means of marker assisted selection. With the aim to identify QTLs, two hundred F3 progenies derived from the cross between the resistant x susceptible genotypes were infected with a fumonisin-producing strain of F. verticillioides with two methods of infection (pinbar and toothpick) in two different locations. 217 SSRs were used to construct a linkage map. SNP markers will be obtained from RNA-Seq. Finally new candidate genes will be considered after metabolic analysis of resistant and susceptible maize genotypes infected with fumonisin producing and fumonisin non-producing strains of F. verticillioides.