Differential location of alpha-expansin proteins during the accommodation of root cells to an arbuscular mycorrhizal fungus.
alpha-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 alpha-expansins was investigated by use of two polyclonal antibodies (anti-EXPA1 and anti-EXPA2, prepared against two different cucumber alpha-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 alpha-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 alpha-expansins. Taken together, the results demonstrate that alpha-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.
Balestrini
R
R
Istituto per la Protezione delle Piante del CNR, Sezione di Micologia and Dipartimento di Biologia Vegetale dell'Università, Viale Mattioli 25, 10125, Turin, Italy.
Cosgrove
D J
DJ
Bonfante
P
P
D002473:Cell Wall / Q000378:metabolism / Q000382:microbiology / Q000648:ultrastructure; D002482:Cellulose / Q000378:metabolism; D018553:Cucumis sativus / Q000378:metabolism* / Q000382:microbiology; D005455:Fluorescent Antibody Technique; D005658:Fungi / Q000502:physiology*; D015870:Gene Expression; D015151:Immunoblotting; D007150:Immunohistochemistry; D046529:Microscopy, Electron, Transmission; D038821:Mycorrhizae / Q000502:physiology*; D010940:Plant Proteins / Q000378:metabolism*; D018517:Plant Roots / Q000166:cytology / Q000382:microbiology* / Q000648:ultrastructure
D010940:Plant Proteins; C095825:expansin protein, plant; D002482:Cellulose