Differential location of α-expansin proteins during the accommodation of root cells to an arbuscular mycorrhizal fungus
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α-Expansins are extracellular proteins that increase plant cell-wall extensibility. We analysed their pattern of expression in cucumber roots in the presence and in the absence of the mycorrhizal fungus, Glomus versiforme. The distribution of α-expansins was investigated by use of two polyclonal antibodies (anti-EXPA1 and anti-EXPA2, prepared against two different cucumber α-expansins) in immunoblotting, immunofluorescence, and immunogold experiments. Immunoblot results indicate the presence of a 30-kDa band specific for mycorrhizal roots. The two antibodies identify antigens with a different distribution in mycorrhizal roots: anti-EXPA1 labels the interface zone, but the plant cell walls only weakly. By contrast, the anti-EXPA2 labels only the plant cell walls. In order to understand the potential role of α-expansins during the accommodation of the fungus inside root cells, we prepared semi-thin sections to measure the size of cortical cells and the thickness of cortical cell walls in mycorrhizal and non-mycorrhizal root. Mycorrhizal cortical cells were significantly larger than non-mycorrhizal cells and had thicker cell walls. In double-labelling experiments with cellobiohydrolase–gold complex, we observed that cellulose was co-localized with α-expansins. Taken together, the results demonstrate that α-expansins are more abundant in the cucumber cell walls upon mycorrhizal infection; we propose that these wall-loosening proteins are directly involved in the accommodation of the fungus by infected cortical cells.
KeywordsArbuscular mycorrhizae Expansin Cell expansion Cellulose Cell wall
This research was funded by the Italian FIRB Project (RBNE01KZE7), by IPP-CNR and CEBIOVEM (D.M. 193/2003) grants. Confocal and electron microscope facilities were available at LMA-Dipartimento di Biologia Vegetale dell’Università di Torino.
- Balestrini R, Josè-Estanyol M, Puigdomènech P, Bonfante P (1997) Hydroxyproline-rich glycoprotein mRNA accumulation in maize root cells colonized by the arbuscular mycorrhizal fungus as revealed by in situ hybridization. Protoplasma 198:36–42Google Scholar
- Bonfante P (2001) At the interface between mycorrhizal fungi and plants: the organization of cell wall, plasma membrane and cytoskeleton. In: Hock B (ed) The mycota IX fungal associations. Springer, Berlin Heidelberg New York, pp 45–61Google Scholar
- Bonfante P, Vian B, Perotto S, Faccio A, Known JP (1990) Cellulose and pectin localization in roots of mycorrhizal Allium porrum: labelling continuity between host cell wall and interfacial material. Planta 180:537–547Google Scholar
- Cho H-T, Cosgrove DJ (2000) Altered expression of expansin modulates leaf growth and pedicel abscission in Arabidopsis thaliana. Proc Natl Acad Sci USA 97:9783–9788Google Scholar
- Cosgrove DJ, Bedinger P, Durachko DM (1997) Group I allergens of grass pollen as cell wall-loosening agents. Proc Natl Acad Sci USA 94:6559–6564Google Scholar
- Kende H, Bradford K, Brummell DA, Cho H-T, Cosgrove DJ, Fleming AJ, Gehring C, Lee Y, McQueen-Mason SJ, Rose JKC, Voesenek LACJ (2004) Nomenclature for members of the expansin superfamily of genes and proteins. Plant Mol Biol (in press)Google Scholar
- Maldonado-Mendoza IE, Harrison MJ (1998) A xyloglucan endo-transglycosylase (XET) gene from Medicago truncatula induced in arbuscular mycorrhizae. In: Abstract from 2nd International Conference on Mycorrhiza, 5–10 July 1998, UppsalaGoogle Scholar
- McQueen-Mason S, Cosgrove DJ (1994) Disruption of hydrogen bonding between wall polymers by proteins that induce plant wall extension. Proc Natl Acad Sci USA 91:6574–6578Google Scholar
- Pien S, Wyrzykowska J, McQueen-Mason S, Smart C, Fleming A (2001) Local expression of expansin induces the entire process of leaf development and modifies leaf shape. Proc Natl Acad Sci USA 98:11812–11817Google Scholar
- Schüßler A, Schwartzott D, Walker C (2001) A new fungal phylum, the Glomeromycota: phylogeny and evolution. Mycol Res 105(12):1413–1421Google Scholar