African Journal of Biotechnology Vol. 6 (14), pp. 1608-1616, 18 July 2007   

ISSN 1684–5315 © 2007 Academic Journals        

Full Length Research Paper

Expression of an expansin carbohydrate-binding module affects xylem and phloem formation

Olawole O. Obembe^{1, 2}, Evert Jacobsen¹, Richard Visser¹ and Jean-Paul Vincken¹*

¹Graduate School Experimental Plant Sciences, Laboratory of Plant Breeding, Wageningen University P O Box 386, 6700 AJ, Wageningen, The Netherlands.

²Department of Biotechnology, The Bells University of Technology, Ota Nigeria.

*Corresponding author. E -mail: jean-paul.vincken@wur.nl. Tel: +31317483998   Fax: +31317483457.

Abbreviations: Cryo-SEM, cryo-scanning electron microscopy; CBM, carbohydrate-binding module; CaMV, cauliflower mosaic virus; PCR, polymerase chain reaction; MS, Murashige-Skoog; NAA, α-naphtalene acetic acid; BAP, 6-benzylaminopurine; rubisco, ribulose 1,5-biphosphate carboxylase/oxygenase.

Accepted 14 June, 2007

Expansins are believed to be involved in disrupting the non-covalent adhesion of cellulose to matrix polysaccharides, thereby promoting wall creep. We have targeted a putative potato expansin (EXPA) carbohydrate-binding module (CBM) to the cell walls of tobacco plants. Histological examinations and electron microscopy indicated that 30% of the xylem cells of the transgenic stems with high expression of the expansin CBM are wider (radial surface area) than those of the controls. Similarly, 37% of the xylem cells of the stems of the high expressers have thinner cell walls than those of the controls. There were no such phenotypes in the low and none expressers, as well as in the control plants. The transgenic tobacco plants expressing the potato expansin CBM did not exhibit marked change in plant morphology. Analysis of cellulose content in the stem cell walls was similar between the high expresser of the transgene and the control plants. Nonetheless, our results taken together demonstrate that expansin CBM alone can bring about changes in the plant cell walls.

Key words: Expansin, carbohydrate binding modules, cell wall modification, homology modelling, cell expansion, transgenic.