Potential role of a maize metallothionein gene in pest resistance

Maize is grown worldwide and much of the world depends on its production, which is lessened by insect and fungal pests. Many maize genes with the potential to improve pest resistance exist in non-functional forms in several inbreds but are functional in those that show resistance. One such gene, encoding a metallothionein protein, was located from a resistance locus of maize inbred GE440, which shows resistance to some Fusarium spp. pathogens. The identified gene, encoding ZmMT10, is disrupted in many maize inbreds, including the commonly used inbred B73. When introduced into maize callus, transformants often significantly increased resistance to F. proliferatum, but were often less effective against F. graminearum. Some transformed callus with the ZmMT10 gene also retarded growth of two classes of insect pests, fall armyworms and corn earworms. Recombinant ZmMT10 was purified from Escherichia coli. The purified protein was found to bind zinc, copper, and nickel and scavenged reactive oxygen species in vitro, which are possible mechanisms for its antiinsect and antifungal activities. In bioassays, the purified protein retarded growth of fall armyworms and corn earworms, but did not show activity against fungi, suggesting that the antifungal activity observed in callus tissue is dependent on the interaction with other plant factors. The inclusion of the identified gene in new plant varieties should increase resistance to both insects and fungi.