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The Induction of Tomato Leucine Aminopeptidase Genes (LapA) After Pseudomonas syringae pv. tomato Infection Is Primarily a Wound Response Triggered by Coronatine

¹Laboratoire de Biologie Cellulaire, Institut National de la Recherche Agronomique, Route de St. Cyr, 78026 Versailles Cédex, France; ²Department of Botany and Plant Sciences, University of California, Riverside 92521-0124; ³Station de Recherches de Lutte Biologique, La Minière, 78285 Guyancourt Cédex, Institut National de la Recherche Agronomique, France

Tomato plants constitutively express a neutral leucine aminopeptidase (LAP-N) and an acidic LAP (LAP-A) during floral development and in leaves in response to insect infestation, wounding, and Pseudomonas syringae pv. tomato infection. To assess the physiological roles of LAP-A, a LapA-antisense construct (35S:asLapA1) was introduced into tomato. The 35S:asLapA1 plants had greatly reduced or showed undetectable levels of LAP-A and LAP-N proteins in healthy and wounded leaves and during floral development. Despite the loss of these aminopeptidases, no global changes in protein profiles were noted. The 35S:asLapA1 plants also exhibited no significant alteration in floral development and did not impact the growth and development of Manduca sexta and P. syringae pv. tomato growth rates during compatible or incompatible infections. To investigate the mechanism underlying the strong induction of LapA upon P. syringae pv. tomato infection, LapA expression was monitored after infection with coronatine-producing and -deficient P. syringae pv. tomato strains. LapA RNA and activity were detected only with the coronatine-producing P. syringae pv. tomato strain. Coronatine treatment of excised shoots caused increases in RNAs for jasmonic acid (JA)-regulated wound-response genes (LapA and pin2) but did not influence expression of a JA-regulated pathogenesis-related protein gene (PR-1). These results indicated that coronatine mimicked the wound response but was insufficient to activate JA-regulated PR genes.

Additional keywords: defense response, exopeptidases, Lycopersicon esculentum, methyl jasmonate, octadecanoid pathway, phytotoxin.