Altered Transcript Abundances in Aspergillus flavus grown on Transgenic Maize Overexpressing a Bacterial Glutamate Dehydrogenase (GDH)

Aspergillus flavus is a filamentous fungus that causes an ear and kernel rot in maize (Zea mays L.). Ear rots are often associated with the accumulation of aflatoxin in the infected plant. The ability of A. flavus to produce aflatoxin depends on the nature and the composition of the substrate. Transgenic maize lines expressing a bacterial NADPH dependent gdhA (glutamate dehydrogenase) gene showed increased nitrogen use efficiency (NUE) based on enhanced nitrogen metabolism with an overall increase in some amino acids in the ear. Studies showed that A. flavus exhibits decreased conidiation and aflatoxin accumulation on GDH⁺ maize lines. The aim here was to use microarray studies to assess changes in the expression patterns of A. flavus genes on GDH⁺ maize.  Used was artificial inoculation in the field of dough stage maize kernels of inbred ‘H99’ transgenic or non transgenic with gdhA. The mRNA was isolated  after harvest. Increased by more than 2 fold on GDH⁺ maize were 747 A. flavus transcripts, only 27 decreased. Hydrolases (EC 3.-), kinases (EC 7.-) and ABC transporters (non-enymatic) were the major protein families increased. No effect on toxin pathway genes was detected. No maize transcripts were increased by GDH⁺, though 95 were reduced significantly by two fold or more including key regulators of C metabolism.  Increased by GDH⁺ were cellulose to lignin ratios; some amino acids; and some toxic products of special nitrogen metabolism. Therefore, the gdhA gene was inferred to confer partial resistance to A. flavus by repressing pathways in a way that lead to altered cell walls and  increased defense metabolite concentrations, pathways different from endogenous resistance mechanisms. Therefore, engineering NUE can have several side benefits for crop production