Signal interactions in pathogen and insect attack: expression of lipoxygenase, proteinase inhibitor II, and pathogenesis-related protein P4 in the tomato, Lycopersicon esculentum

Pathogens and insects can elicit different sets of plant host responses, su pporting the hypothesis for control by different signaling pathways. To eva luate the potential for signal interaction in plants attacked by pathogens and insects, the mRNA abundance for lipoxygenase (LOX), a wound-inducible p roteinase inhibitor (PINII), and a pathogenesis-related protein (P4) was ev aluated,in tomato leaves following challenge with a variety of agents. PINI I and P4 expression was determined as these proteins are induced in tomato leaves characteristically following attack by certain insects or pathogens, respectively. Expression studies of LOX, PINII, and P4 indicate that their induction in tomato does not follow a strict pattern based on the type of biologic inducer (insect vs, pathogen) or chemical treatment, with each spe cific treatment inducing a distinct pattern of gene expression. However, pl ants induced to express disease resistance with the synthetic salicylate mi mic benzothiadiazole-7-carbothioic acid S-methyl ester were compromised in their expression of the wound- or jasmonate-activated PINII, consistent wit h an observed increase in susceptibility to insect herbivory reported in a companion study. The results do not support the hypothesis for a strict dic hotomy of signaling by insects and pathogens of LOX, PINII and P4 in tomato , but point to a potential vulnerability of acquired resistance evident at the levels of gene expression and response to insect attack. (C) 1999 Acade mic Press.