A wound- and systemin-inducible polygalacturonase in tomato leaves

Oligogalacturonide fragments that activate defensive genes in plant leaves heretofore have been thought to be generated only by pathogen-derived pecti n-degrading enzymes, because polygalacturonase (PG) activity has not been r eported in leaves. Here, we report that mRNAs encoding a PG catalytic subun it protein and its regulatory (beta-subunit) protein are expressed in tomat o leaves in response to wounding, systemin, and oligosaccharide elicitors. Synthesis of the two subunits in response to wounding is systemic and is ac companied by an increase in PG activity in extracts from both wounded and u nwounded leaves. The finding that PG subunit mRNAs and PG enzyme activity a re induced by wounding indicates that herbivore attacks can produce endogen ous oligogalacturonide elicitors that may be involved in the local and syst emic activation of defense responses against both herbivores and pathogens.