Abstract
Polyamine oxidase (PAO) catalyzes the oxidative catabolism of spermidine and spermine, generating hydrogen peroxide. In wild-type tobacco (Nicotiana tabacum 'Xanthi') plants, infection by the compatible pathogen Pseudomonas syringae pv tabaci resulted in increased PAO gene and corresponding PAO enzyme activities; polyamine homeostasis was maintained by induction of the arginine decarboxylase pathway and spermine was excreted into the apoplast, where it was oxidized by the enhanced apoplastic PAO, resulting in higher hydrogen peroxide accumulation. Moreover, plants overexpressing PAO showed preinduced disease tolerance against the biotrophic bacterium P. syringae pv tabaci and the hemibiotrophic oomycete Phytophthora parasitica var nicotianae but not against the Cucumber mosaic virus. Furthermore, in transgenic PAO-overexpressing plants, systemic acquired resistance marker genes as well as a pronounced increase in the cell wall-based defense were found before inoculation. These results reveal that PAO is a nodal point in a specific apoplast-localized plant-pathogen interaction, which also signals parallel defense responses, thus preventing pathogen colonization. This strategy presents a novel approach for producing transgenic plants resistant to a broad spectrum of plant pathogens.
Highlights
Polyamine oxidase (PAO) catalyzes the oxidative catabolism of spermidine and spermine, generating hydrogen peroxide
In wild-type tobacco leaves infiltrated with the pathogenic bacterium PS strain SFP-2124, PAO was an early-responsive gene; the abundance of its transcript level increased significantly at 12 h postinoculation compared with the corresponding control, as shown by reverse transcription (RT)-PCR analysis (Fig. 1A; NtPAO gene)
We showed recently that abiotic stress induces secretion of Spd into the apoplastic compartment, where it is oxidized by the cell wall-associated PAO; the generated H2O2, depending on its size, signals either molecular stress defense responses or programmed cell death (PCD) (Moschou et al, 2008c)
Summary
Polyamine oxidase (PAO) catalyzes the oxidative catabolism of spermidine and spermine, generating hydrogen peroxide. In transgenic PAO-overexpressing plants, systemic acquired resistance marker genes as well as a pronounced increase in the cell wall-based defense were found before inoculation. These results reveal that PAO is a nodal point in a specific apoplast-localized plant-pathogen interaction, which signals parallel defense responses, preventing pathogen colonization. Polyamine Oxidase Restricts Pathogens levels (“signatures”) and the intracellular PA homeostasis, the generated H2O2 signals tolerance-effector genes to abiotic stress or induces the execution of the programmed cell death (PCD) syndrome (Moschou et al, 2008a)
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