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A Symbiotic Plant Peroxidase Involved in Bacterial Invasion of the Tropical Legume Sesbania rostrata^{1,[C],[W],[OA]}

Department of Plant Systems Biology, Flanders Institute for Biotechnology, and Department of Molecular Genetics, Ghent University, B–9052 Ghent, Belgium

Aquatic nodulation on the tropical legume Sesbania rostrata occurs at lateral root bases via intercellular crack-entry invasion. A gene was identified (Srprx1) that is transiently up-regulated during the nodulation process and codes for a functional class III plant peroxidase. The expression strictly depended on bacterial nodulation factors (NFs) and could be modulated by hydrogen peroxide, a downstream signal for crack-entry invasion. Expression was not induced after wounding or pathogen attack, indicating that the peroxidase is a symbiosis-specific isoform. In situ hybridization showed Srprx1 transcripts around bacterial infection pockets and infection threads until they reached the central tissue of the nodule. A root nodule extensin (SrRNE1) colocalized with Srprx1 both in time and space and had the same NF requirement, suggesting a function in a similar process. Finally, in mixed inoculation nodules that were invaded by NF-deficient bacteria and differed in infection thread progression, infection-associated peroxidase transcripts were not observed. Lack of Srprx1 gene expression could be one of the causes for the aberrant structure of the infection threads.

² These authors contributed equally to the article.

³ Present address: Department of Medical Protein Research, Flanders Institute for Biotechnology, Ghent University, Albert Baertsoenkaai 3, B–9000 Ghent, Belgium.

The authors 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) are: Marcelle Holsters (marcelle.holsters{at}psb.ugent.be) and Sofie Goormachtig (sofie.goormachtig{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.

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www.plantphysiol.org/cgi/doi/10.1104/pp.107.098764

^* Corresponding author; e-mail marcelle.holsters{at}psb.ugent.be; fax 32–9–3313809.

Received March 1, 2007; accepted March 22, 2007; published March 23, 2007.

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