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Induction of Hydroxycinnamoyl-Tyramine Conjugates in Pepper by Xanthomonas campestris, a Plant Defense Response Activated by hrp Gene-Dependent and hrp Gene-Independent Mechanisms

June 2001 , Volume 14 , Number  6
Pages  785 - 792

Mari-Anne Newman , 1 Edda von Roepenack-Lahaye , 1 Adrian Parr , 2 Michael J. Daniels , 1 and J. Maxwell Dow 1

1The Sainsbury Laboratory, John Innes Centre, Norwich Research Park, Colney Lane, Norwich NR4 7UH, U.K.; 2Institute of Food Research, Norwich Research Park, Colney Lane, Norwich NR4 7UH, U.K.

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Accepted 23 February 2001.

Inoculation of pepper leaves, Capsicum annuum cv. Early Calwonder ECW 10R, with strains of Xanthomonas campestris led to an accumulation of the phenolic conjugates feruloyltyramine (FT) and p-coumaroyltyramine (CT) 24 h postinoculation in nonhost- and gene-for-gene-determined incompatible interactions with X. campestris pv. campestris and X. campestris pv. vesicatoria, respectively. In contrast, neither compound was detected in compatible interactions with X. campestris pv. vesicatoria. The accumulation of FT and CT was preceded by an increase in the extractable activity of tyrosine decarboxylase as well as increases in the transcription of genes encoding phenylalanine ammonia-lyase and tyramine hydroxycinnamoyl transferase. No such changes were detected in compatible interactions. Very rapid accumulation of FT and CT occurred (4 h postinoculation) in pepper in response to a X. campestris pv. campestris mutant carrying a deletion of the hrp gene cluster. In contrast, hrp mutants of X. campestris pv. vesicatoria failed to elicit the production of FT and CT. These observations suggest the existence of hrp gene-dependent and -independent activation mechanisms of a defense response involving hydroxycinnamoyltyramines.

Additional keywords: antibacterial compounds ; avrBs1 avirulence gene ; Bs1 resistance gene.

© 2001 The American Phytopathological Society