Role of AREA, a regulator of nitrogen metabolism, during colonization of maize kernels and fumonisin biosynthesis in Fusarium verticillioides

Fumonisin B1 (FB1) biosynthesis is repressed in cultures containing ammonium as the nitrogen source and when grown on blister kernels, the earliest stages of kernel development. In this study AREA, a regulator of nitrogen metabolism, was disrupted in Fusarium verticilliodes. The mutant (ΔareA) grew poorly on mature maize kernels, but grew similar to wild type (WT) with the addition of ammonium phosphate. FB1 was not produced by ΔareA under any condition or by the WT with added ammonium phosphate. Constitutive expression of AREA (strain AREA-CE) rescued the growth and FB1 defects in ΔareA. Growth of WT, ΔareA, and AREA-CE on blister-stage kernels was similar. After 7 days of growth, none of the strains produced FB1 and the pH of the kernel tissues was 8.0. Addition of amylopectin to the blister kernels resulted in a pH near 6.6 and FB1 production by WT and AREA-CE. The results support the hypothesis that FB1 biosynthesis is regulated by AREA. Also the failure to produce FB1 in blister kernels is due to high pH conditions generated because of an unfavorable carbon/nitrogen environment.