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First published online December 31, 2008; 10.1104/pp.108.131797 Plant Physiology 149:1387-1398 (2009) © 2009 American Society of Plant Biologists OPEN ACCESS ARTICLE
Eternal Youth, the Fate of Developing Arabidopsis Leaves upon Rhodococcus fascians Infection1,[C],[W],[OA]Department of Plant Systems Biology, Flanders Institute for Biotechnology, and Department of Plant Biotechnology and Genetics, Ghent University, 9052 Ghent, Belgium
The phytopathogenic actinomycete Rhodococcus fascians induces neoplastic shooty outgrowths on infected hosts. Upon R. fascians infection of Arabidopsis (Arabidopsis thaliana), leaves are formed with small narrow lamina and serrated margins. These symptomatic leaves exhibit reduced tissue differentiation, display more but smaller cells that do not endoreduplicate, and accumulate in the G1 phase of the cell cycle. Together, these features imply that leaf growth occurs primarily through mitotic cell division and not via cell expansion. Molecular analysis revealed that cell cycle gene expression is activated continuously throughout symptomatic leaf development, ensuring persistent mitotic cycling and inhibition of cell cycle exit. The transition at the two major cell cycle checkpoints is stimulated as a direct consequence of the R. fascians signals. The extremely reduced phenotypical response of a cyclind3;1-3 triple knockout mutant indicates that the D-type cyclin/retinoblastoma/E2F transcription factor pathway, as a major mediator of cell growth and cell cycle progression, plays a key role in symptom development and is instrumental for the sustained G1-to-S and G2-to-M transitions during symptomatic leaf growth.
1 This work was supported by the Bijzonder Onderzoeksfonds of Ghent University (predoctoral fellowship to S.D.). 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). [C] Some figures in this article are displayed in color online but in black and white in the print edition. [W] The online version of this article contains Web-only data. [OA] Open Access articles can be viewed online without a subscription. www.plantphysiol.org/cgi/doi/10.1104/pp.108.131797 * Corresponding author; e-mail marcelle.holsters{at}psb.ugent.be. Received October 28, 2008; accepted December 25, 2008; published December 31, 2008. Related articles in Plant Physiol.:
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