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.