plant surface microbiology.pdf

18 Mycorrhizal Development and Cytoskeleton
Marjatta Raudaskoski, Mika Tarkka and Sara Niini
1 Introduction
The formation of mycorrhiza requires morphological changes, both in the
plant cells and fungal hyphae, necessary for the development and maintenance
of the signal and nutrient exchange at plant fungal interfaces. It is well
known that cytoskeletal elements play a central role both in the morphogenesis
of plant root cells (Barlow and Baluška 2000) and of fungal hyphae (Raudaskoski
et al. 2001). In the present review, the plant and fungal genes encoding
the structural proteins of main cytoskeletal elements, microtubules (MTs)
and microfilaments (MFs), are described. Some speculations of the functional
significance of cytoskeletal rearrangements observed in plant cells and fungal
hyphae at the formation of endo- and ectomycorrhiza are presented. The
reorganization of the cytoskeleton results from interactions with proteins that
serve by themselves as targets for intra- and extracellular signal mediating
pathways (Johnson 1999; Kost et al. 1999b). The presence of such pathways in
mycorrhiza is discussed. The different phases in the cell cycle also requires
rearrangements in the cytoskeleton (Mews et al. 1997; John et al. 2001). This
aspect is shortly discussed in association with known effects of mycorrhiza
on the plant cell cycle. Finally, the general methods used in visualization of
cytoskeletal components are shortly introduced.
2 Cytoskeletal Components
The cytoskeleton is composed of filamentous structures whose arrangements
are continuously changing in living cells in response to different developmental
and environmental cues. In plant and fungal cells there are two main
cytoskeletal proteins: actin and tubulin. Actin monomers polymerize to thin
filaments known as MFs or actin filaments. Tubulin polymerizes to MTs. Both
MFs and MTs are polarized structures with minus and plus ends. The minus
end is often attached to some subcellular structure while the plus end is
Plant Surface Microbiology
A.Varma, L. Abbott, D. Werner, R. Hampp (Eds.)
© Springer-Verlag Berlin Heidelberg 2004