Link to home

Regulatory Interactions Between Quorum-Sensing, Auxin, Cytokinin, and the Hrp Regulon in Relation to Gall Formation and Epiphytic Fitness of Pantoea agglomerans pv. gypsophilae

July 2009 , Volume 22 , Number  7
Pages  849 - 856

Laura Chalupowicz,1,2 Isaac Barash,2 Mary Panijel,2 Guido Sessa,2 and Shulamit Manulis-Sasson1

1Department of Plant Pathology and Weed Research, ARO, the Volcani Center, Bet Dagan, 50250, Israel; 2Department of Plant Sciences, Tel-Aviv University, Tel-Aviv 69978, Israel

Go to article:
Accepted 9 March 2009.

Gall formation by Pantoea agglomerans pv. gypsophilae is controlled by hrp/hrc genes, phytohormones, and the quorum-sensing (QS) regulatory system. The interactions between these three components were investigated. Disruption of the QS genes pagI and pagR and deletion of both substantially reduced the transcription levels of the hrp regulatory genes hrpXY, hrpS, and hrpL, as determined by quantitative reverse-transcriptase polymerase chain reaction. Expression of hrpL in planta was inhibited by addition of 20 μM or higher concentrations of the QS signal C4-HSL. The pagR and hrpL mutants caused an equivalent reduction of 1.3 orders in bacterial multiplication on bean leaves, suggesting possible mediation of the QS effect on epiphytic fitness of P. agglomerans pv. gypsophilae by the hrp regulatory system. indole-3-acetic acid (IAA) and cytokinin significantly affected the expression of the QS and hrp regulatory genes. Transcription of pagI, pagR, hrpL, and hrpS in planta was substantially reduced in iaaH mutant (disrupted in IAA biosynthesis via the indole-3-acetamide pathway) and etz mutant (disrupted in cytokinin biosynthesis). In contrast, the ipdC mutant (disrupted in IAA biosynthesis via the indole-3-pyruvate pathway) substantially increased expression of pagI, pagR, hrpL, and hrpS. Results presented suggest the involvement of IAA and cytokinins in regulation of the QS system and hrp regulatory genes.

© 2009 The American Phytopathological Society