Studying gene expression in fungus and planta to understand the interaction Fusarium verticillioides-maize.

Fusarium verticillioides is a plant pathogen able to produce fumonisin in maize kernels. A study on the pathosystem F. verticillioides-maize has been developed speculating on both in vitro and in planta perspectives. The former studied the effects of temperature (T) and water activity (aw) on fumonisin B (FB) production and expression of FUM genes 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 FUM gene expression was sensibly affected by aw, rather than T, indicating that fungal 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, similarly to FB production, underlining that gene expression and secondary metabolite production followed the same trend. At 21 days of incubation, FUM14 and FUM3 -regulating the production of FB1 and FB2 from FB3 and FB4, respectively,- were maximally expressed, while FUM21 –coding for a transcription factor for FB biosynthesis - was 10x less expressed; aw=0.900 was inhibitory for culture growth and FB production. 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.