Ezra, D., Department of Plant Pathology, ARO, Volcani Center, Bet Dagan, 50250, Israel, Department of Plant Sciences, Faculty of Life Sciences, Tel-Aviv University, Tel-Aviv 69978, Israel
Barash, I., Department of Plant Sciences, Faculty of Life Sciences, Tel-Aviv University, Tel-Aviv 69978, Israel
Weinthal, D.M., Department of Plant Pathology, ARO, Volcani Center, Bet Dagan, 50250, Israel, Department of Plant Sciences, Faculty of Life Sciences, Tel-Aviv University, Tel-Aviv 69978, Israel
Gaba, V., Department of Virology, ARO, Volcani Center, Bet Dagan, 50250, Israel
Manulis, S., Department of Plant Pathology, ARO, Volcani Center, Bet Dagan, 50250, Israel

Pantoea agglomerans pv. gypsophilae (Pag) causes root and crown gall disease on gypsophila, whereas P. agglomerans pv. betae (Pab) induces the disease on beet as well as gypsophila. Both pathovars harbour a pathogenicity plasmid (pPATHPag or pPATHPab) that determines disease development. We have previously isolated and partially characterized a pleiotropic gene from the pPATHPag, designated as pthG, that encodes a virulence factor in gypsophila and an elicitor of a hypersensitive-like response in beet roots. The present study was undertaken to characterize pthG further as an avr gene. The infiltration of beet leaves with strains expressing PthG (i.e. Pag or Pab containing pthG in trans) caused an hypersensitive reaction (HR) response within 48 h, whereas strains lacking intact pthG (i.e. Pab or Pag mutated in pthG) resulted in gall formation after 5 days. A hypersensitive reaction was elicited by PthG on multiple beet species, whereas a marker exchange mutant of Pag in pthG extended its host range on these beet species. A marker exchange mutant of Pag in hrpJ, encoding a component of the Type III secretion system, prevented HR elicitation. Mutations in each of the hrp regulatory genes (hrpY, hrpS and hrpL) substantially reduced the transcriptional activity of pthG in gypsophila cuttings. PthG could only be detected inside Pag cells during over-expression of hrpS or hrpL Particle bombardment of GFP-PthG fusion caused cell death in beet, but not in non-host (melon) leaves. Present and previous results have established pthG as a broad-host-range avr gene that functions in multiple host plant species and the first functional avr gene in Pantoea spp.