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Research article - Peer-reviewed, 2008

Modulation of the hormone setting by Rhodococcus fascians results in ectopic KNOX activation in Arabidopsis

Depuydt, Stephen; Dolezal, Karel; Van Lijsebettens, Mieke; Moritz, Thomas; Holsters, Marcelle; Vereecke, Danny


The biotrophic actinomycete Rhodococcus fascians has a profound impact on plant development and a common aspect of the symptomatology is the deformation of infected leaves. In Arabidopsis ( Arabidopsis thaliana), the serrated leaf margins formed upon infection resemble the leaf phenotype of transgenic plants with ectopic expression of KNOTTED-like homeobox (KNOX) genes. Through transcript profiling, we demonstrate that class-I KNOX genes are transcribed in symptomatic leaves. Functional analysis revealed that BREVIPEDICELLUS/KNOTTED-LIKE1 and mainly SHOOT MERISTEMLESS were essential for the observed leaf dissection. However, these results also positioned the KNOX genes downstream in the signaling cascade triggered by R. fascians infection. The much faster activation of ARABIDOPSIS RESPONSE REGULATOR5 and the establishment of homeostatic and feedback mechanisms to control cytokinin (CK) levels support the overrepresentation of this hormone in infected plants due to the secretion by the pathogen, thereby placing the CK response high up in the cascade. Hormone measurements show a net decrease of tested CKs, indicating either that secretion by the bacterium and degradation by the plant are in balance, or, as suggested by the strong reaction of 35S:CKX plants, that other CKs are at play. At early time points of the interaction, activation of gibberellin 2-oxidase presumably installs a local hormonal setting favorable for meristematic activity that provokes leaf serrations. The results are discussed in the context of symptom development, evasion of plant defense, and the establishment of a specific niche by R. fascians.

Published in

Plant Physiology
2008, volume: 146, number: 3, pages: 1267-1281

Authors' information

Depuydt, Stephen
Ghent University
Dolezal, Karel
Swedish University of Agricultural Sciences, Department of Forest Genetics and Plant Physiology
Dolezal, Karel
Palacký University Olomouc
Dolezal, Karel
The Czech Academy of Sciences
Van Lijsebettens, Mieke
Ghent University
Swedish University of Agricultural Sciences, Department of Forest Genetics and Plant Physiology
Holsters, Marcelle
Ghent University
Vereecke, Danny
Ghent University

UKÄ Subject classification

Forest Science

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