p-Coumaroylnoradrenaline, a novel plant metabolite implicated in tomato defense against pathogens.

The Avr9 peptide elicitor from the fungus Cladosporium fulvum, the bacterial pathogen Pseudomonas syringae pathovar tomato carrying the avirulence gene avrPto (Pst (avrPto)), and the organophosphorous insecticide fenitrothion induce resistance-related responses in tomato lines carrying the Cf-9, Pto, and Fen genes, respectively. These responses were associated with synthesis of p-coumaroyloctopamine and p-coumaroylnoradrenaline, a novel compound for plants. In susceptible near isogenic tomato lines (Cf-0, pto, fen) and wounded tomato leaves, the levels of these compounds were reduced or undetectable. The elevated levels of p-coumaroyloctopamine and p-coumaroylnoradrenaline were accompanied by elevated mRNA levels of genes encoding phenylalanine ammonia lyase, p-coumarate CoA ligase, and hydroxycinnamoyl-CoA:tyramine N-(hydroxycinnamoyl)transferase (THT), enzymes that are involved in the hydroxycinnamic acid amide biosynthesis. Southern hybridization indicated that THT is encoded by a multigene family in tomato. Four different THT full-length cDNAs were derived by reverse transcriptase-PCR using degenerate primers based on potato and tobacco THT sequences. Transcripts for all four homologs were present in unchallenged tomato leaves, but only tomTHT1-3 was highly expressed following challenge with Pst (avrPto). Furthermore, tomTHT1-3 showed a more substantial and rapid induction in the incompatible interaction than in the compatible interaction. The cDNAs tomTHT1-3, tomTHT7-1, and tomTHT7-8 encoded proteins with a high degree of amino acid sequence homology, although the recombinant proteins had different preferences for octopamine and noradrenaline. The fourth cDNA, tomTHT1-4, directed synthesis of a truncated enzymatically inactive protein due to the presence of a premature stop codon.