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PLANTS INTERACTING WITH OTHER ORGANISMS

Modulation of the Hormone Setting by Rhodococcus fascians Results in Ectopic KNOX Activation in Arabidopsis^1,[W],[OA]

Stephen Depuydt, Karel Doleal, Mieke Van Lijsebettens, Thomas Moritz, Marcelle Holsters^* and Danny Vereecke

Department of Plant Systems Biology, Flanders Institute for Biotechnology, and Department of Molecular Genetics, Ghent University, 9052 Gent, Belgium (S.D., M.V.L., M.H., D.V.); Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, SE–90183 Umeå, Sweden (K.D., T.M.); and Laboratory of Growth Regulators, Palack University and Institute of Experimental Botany, Academy of Sciences of the Czech Republic, 783 71 Olomouc, Czech Republic (K.D.)

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.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Danny Vereecke (danny.vereecke{at}psb.ugent.be).

^[W] The online version of this article contains Web-only data.

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www.plantphysiol.org/cgi/doi/10.1104/pp.107.113969

^* Corresponding author; e-mail marcelle.holsters{at}psb.ugent.be.

Received November 26, 2007; accepted January 3, 2008; published January 9, 2008.

This article has been cited by other articles:

				S. Depuydt, L. De Veylder, M. Holsters, and D. Vereecke Eternal Youth, the Fate of Developing Arabidopsis Leaves upon Rhodococcus fascians Infection Plant Physiology, March 1, 2009; 149(3): 1387 - 1398. [Abstract] [Full Text] [PDF]

				S. Depuydt, S. Trenkamp, A. R. Fernie, S. Elftieh, J.-P. Renou, M. Vuylsteke, M. Holsters, and D. Vereecke An Integrated Genomics Approach to Define Niche Establishment by Rhodococcus fascians Plant Physiology, March 1, 2009; 149(3): 1366 - 1386. [Abstract] [Full Text] [PDF]

				I. Pertry, K. Vaclavikova, S. Depuydt, P. Galuszka, L. Spichal, W. Temmerman, E. Stes, T. Schmulling, T. Kakimoto, M. C. E. Van Montagu, et al. Identification of Rhodococcus fascians cytokinins and their modus operandi to reshape the plant PNAS, January 20, 2009; 106(3): 929 - 934. [Abstract] [Full Text] [PDF]