1.1.21
SYRINGOLIN, A NOVEL DEPSIPEPTIDE ELICITOR FROM PSEUDOMONAS SYRINGAE PV. SYRINGAE THAT INDUCES DISEASE RESISTANCE IN RICE

U WAESPI 1, T WINKLER2, E FREYDL1, PO HASSA1 and R DUDLER1

1Institute for Plant Biology, University of Zurich, Switzerland; 2Novartis AG, Basel, Switzerland

Background and objectives
Local acquired resistance of rice (Oryza sativa) against the rice blast fungus Pyricularia oryzae can be induced by inoculation of rice leaves with the non-host pathogen Pseudomonas syringae pv. syringae. Complementary DNAs have been cloned in our laboratory that correspond to transcripts accumulating concomitantly with resistance induction. We are interested in the molecular recognition of the pathogen and in the signalling cascade leading to gene induction.

Results and conclusions
An elicitor of defence responses in rice derived from Pseudomonas syringae pv. syringae has been purified to homogeneity by gel permeation chromatography and RP-HPLC. By NMR and MS analysis the structure of the compound, which we refer to as syringolin, could be elucidated. Syringolin is a novel and unusual cyclic tetrapeptide of molecular mass 493 Da, consisting of a 12-membered ring formed by two non-proteinogenic amino acids connected to valine and by a urea bond to another valine. Syringolin induces the whole set of resistance-associated genes and resistance against Pyricularia oryzae in rice. In vitro it is not toxic against Pyricularia oryzae. Syringolin induces Pir7b protein in amounts as low as 250 fMol per leaflet.

Syringolin is one, but not the only, active principle by which Pseudomonas syringae pv. syringae strains induce resistance in rice plants. Strain SM does not produce syringolin, but does induce resistance against Pyricularia oryzae, indicating another inducing principle involved. We are now looking for a receptor for syringolin in rice and are interested in the signalling cascade leading to gene induction.