Inhibiting the α-amylase from Aspergillus flavus: A novel approach to reduce aflatoxin contamination in corn

The fungus Aspergillus flavus is a ubiquitous pathogen of corn, figs, pistachio, cotton and nut trees. On corn, aspergillus causes an ear and kernel rot especially when the plants are stressed by drought, heat or insect injuries. Fungal infections result in the production of aflatoxins, a series of structurally related compounds known to be carcinogenic. In an attempt to identify host factors involved in aflatoxin biosynthesis, simple sugars were found to induce toxin production. α-amylases are endoglucuronidases produced by many organisms to digest starch into simple sugars. Disruption of Amy1, the α-amylase gene in A. flavus, limited the ability of the fungus to produce aflatoxin in the endosperms of infected corn kernels. A number of α-amylase inhibitors have been isolated from plants and have been found to enhance resistance against insects. They are known to be very specific in their action, and none of the characterized inhibitors affected fungal α-amylases. We screened plant sources for inhibitors of A. flavus α-amylase and identified a 36-kDa protein from the legume Lablab purpureus. The α-amylase inhibitor from Lablab purpureus, AILP, was purified and characterized. AILP inhibits α-amylases from A. flavus as well as those produced by a number of other fungi, but does not inhibit α-amylases from animal and plant sources. The N-terminal sequence of AILP shows high similarity to a lectin identified in Phaseolus acutifolius and to an α-amylase-like inhibitor from Phaseolus lunatus. AILP has anti-fungal activities affecting both conidial germination and hyphal growth of A. flavus. Inhibiting the α-amylase from A. flavus reduces the ability of the fungus to produce aflatoxin on infected kernels. Introducing the gene encoding for AIL in corn hybrids may therefore enhance their resistance to A. flavus