Fusarium verticillioides-maize: a gene expression approach to study the fungus-planta interactions.

Fusarium verticillioides is a filamentous fungus, worldwide pathogen of maize, on which it causes Fusarium ear rot and it is able to produce fumonisin. A study on the interaction between F. verticillioides and its main host-maize has been carried on, considering both in vitro and in planta perspectives. The former studied the effects of water activity (aw) and temperature (T) on fumonisin B (FB) production and expression of FUM genes (FUM2-FUM3-FUM8-FUM13- FUM14-FUM21) in F.verticillioides strains. The latter monitored which genes were differentially expressed in resistant and susceptible maize lines at several time points after inoculation by a fumonisin-producing strain of F. verticillioides. The in vitro study showed that aw had a significant influence on FUM gene expression rather than T, indicating that fungal secondary metabolism is more overturned by low aw than by T decrease. Most of FUM genes were highly expressed at aw=0.990 compared to 0.955, and the same was observed for FB production. This common trend suggests that even if the expression of genes and the product of the metabolite are far events in terms of “biochemical times”, a close regulation of FUM gene expression and production of FB can subsist. At 21 days of incubation, FUM14 and FUM3 -regulating the production of FB1 and FB2 from FB3 and FB4, respectively,- were maximally expressed. On the contrary FUM21 –coding for a transcription factor for FB biosynthesis - was 10x less expressed. The in planta study showed that in kernels at 48 h after inoculation (hai) about 800 genes were differentially regulated and nearly 10% assigned to the defence category. During the very early stages of incubation a small proportion of the host transcripts was induced and none of them was involved in defence processes. Early response genes encoded signalling or regulatory components. The highest number of differentially expressed genes was attained at 48 hai. The late response genes encoded effector proteins. When resistant and susceptible maize genotypes were compared, in the resistant line the expression of defence genes was detected before inoculation, while in the susceptible genotype they were induced only after pathogen inoculation. The identification of differentially expressed plant genes that interact with the fungus will produce useful tools to detect candidate genes, useful to select resistant maize genotypes by means of marker assisted selection.