A unique 33-kD cysteine proteinase accumulates in response to larval feeding in maize genotypes resistant to fall armyworm and other Lepidoptera.

Plants respond to insect feeding with a number of defense mechanisms. Using maize genotypes derived from Antiquan germ plasm that are resistant to Lepidoptera, we have demonstrated that a unique 33-kD cysteine proteinase accumulates in the whorl in response to larval feeding. The abundance of the proteinase increased dramatically at the site of larval feeding after 1 hr of infestation and continued to accumulate for as long as 7 days. The 33-kD cysteine proteinase was most abundant in the yellow-green portion of the whorl-the normal site of larval feeding and the tissue that has the greatest inhibitory effect on larval growth in bioassays. The proteinase was expressed in response to wounding and was found in senescent leaves. It may be a marker of programmed cell death. The gene coding for the proteinase, mir1, has been transformed into Black Mexican Sweet callus. When larvae were reared on callus expressing the proteinase, their growth was inhibited approximately 60 to 80%. The expression of a cysteine proteinase, instead of a cysteine proteinase inhibitor, may be a novel insect defense mechanism in plants.