, Volume 195, Issue 2, pp 175-181

Extensin gene expression is induced by mechanical stimuli leading to local cell wall strengthening in Nicotiana plumbaginifolia

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Abstract

Nicotiana plumbaginifolia Viv. harbors a single extensin gene, although related hydroxyproline-rich sequences are present in the genome. Northern analysis showed that the gene is highly expressed in roots and to a lesser extent in stems. Expression in leaves is low but mRNA levels are increased upon infection with the incompatible bacterium Pseudomonas syringae. Extensin transcript levels in leaves were slightly enhanced after wounding and salicylic acid treatment. In-situ hybridization experiments showed high accumulation of extensin mRNA in cells which, at certain stages of development, require reinforcement of their cell walls. The cortical cells in stem nodes and roots, which are put under severe mechanical stress by adjacent developing tissues, tend to express the gene to high levels. Immunolocalization of the extensin protein in stems and roots demonstrated a close association of the protein with lignin deposition. Mature tissues contained more extensin than younger tissues. The extensin promoter was fused to the β-glucuronidase gene.

The authors wish to thank Tom Gerats (Laboratorium voor Genetica, Universiteit Gent, Gent, Belgium) for reading the manuscript, D.J. Meyer (University of Nebraska, Neb., USA) and D.W. Galbraith (University of Arizona, Ariz., USA), and J. Ellis (University of Warwick, Coventry, UK) for providing the antibody 11D2 and the antibody directed against the chlorophyll a/b-binding protein, respectively, Vera Vermaercke and Karel Spruyt for preparing the figures, and Mieke Wynendaele for technical assistance. This work was supported by grants from the Belgian Programme on Interuniversity Poles of Attraction (Prime Minister's Office, Science Policy Programming, #38) and the “Vlaams Actieprogramma Biotechnologie” (ETC 002).