Poster Session: MPMI-Bacteria

570-P

Polar auxin transport is mandatory for gall formation by Pantoea agglomerans on gypsophila.
L. Chalupowicz (1), D. Weinthal (1), V. Gaba (1), G. Sessa (2), I. BARASH (2), S. Manulis-Sasson (1)
(1) ARO The Volcani Center, Bet Dagan, Israel; (2) Tel Aviv University, Tel Aviv, Israel

Virulence of Pantoea agglomerans pv. gypsophilae (Pag) on gypsophila is dependent on the pPATH plasmid containing a functional hrp/hrc gene cluster, genes encoding for type III effectors and a cluster of genes for biosynthesis of indole-3-acetic acid (IAA) and cytokinin (CK). Mutation in the hrp/hrc gene cluster abolished gall formation, whereas simultaneous inactivation of the pathways for IAA and CK biosynthesis reduced gall size by only 50%. The hypothesis that plant-produced IAA is involved in gall development was tested by disruption of polar auxin transport with the specific inhibitors 2,3,5-tri-iodobenzoic acid (TIBA) or N-1-naphthylphthalamic acid (NPA) applied as a lanolin ring around gypsophila stems. Pag inoculation was performed below and above the lanolin rings containing TIBA or NPA. Galls were developed above rings containing either TIBA or NPA, but not below. Colonization of Pag was reduced by 2 orders of magnitude after 96h on inoculated gypsophila stems below the lanolin-TIBA ring. Transcription of the hrp regulatory gene hrpL and the quorum sensing-regulatory gene pagR were significantly reduced in Pag inoculated-stem below the TIBA treatment. Expression of a putative auxin efflux carrier PIN2 was significantly affected in Pag-inoculated gypsophila at initial 24h. Results presented demonstrate that plant-produced auxin is crucial for gall formation as opposed to the significant but secondary role of pathogen-produced IAA.