Identification of a Bioactive Bowman–Birk Inhibitor from an Insect-Resistant Early Maize Inbred

Breeding
of maize, Zea mays, has
improved insect resistance, but the genetic and biochemical basis
of many of these improvements is unknown. Maize oligonucleotide microarrays
were utilized to identify differentially expressed genes in leaves
of three maize inbreds, parents Oh40B and W8 and progeny Oh43, developed
in the 1940s. Oh43 had enhanced leaf resistance to corn earworm larvae, Helicoverpa zea, and fall armyworm larvae, Spodoptera frugiperda, compared to one or both parents.
Among ca. 100 significantly differentially expressed genes, expression
of a Bowman–Birk trypsin inhibitor (BBI) gene was at least
ca. 8-fold higher in Oh43 than in either parent. The Oh43 BBI gene
was expressed as a recombinant protein. Purified BBI inhibited trypsin
and the growth of fall armyworm larvae when added to insect diet.
These experiments indicate that comparative gene expression analysis
combined with insect resistance measurements of early inbreds can
identify previously unrecognized resistance genes.