plant surface microbiology.pdf

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Marjatta Raudaskoski, Mika Tarkka and Sara Niini
analyzed sample represented a pool of young and mature ectomycorrhizal
roots. In the future, the analysis of different developmental stages of ectomycorrhiza
might improve our understanding of the expression pattern of the S.
bovinus actin genes in symbiosis. From S. commune, a nonectomycorrhizal
homobasidiomycete closely related to S. bovinus, two actin-encoding genes
were also isolated (Tarkka et al. 2000), which indicates that filamentous
homobasidiomycetes differ from filamentous deutero- and ascomycetes, having
only a single actin gene. Recently, two actin-encoding genes have also
been identified in the genome sequence of Schizosaccharomyces pombe
(Wood et al. 2002).
3 Organization of Cytoskeleton in Endomycorrhiza
3.1 Root Cells
Indirect immunofluorescence (IIF) microscopy and related methods have been
used to study the structure of the cytoskeleton in nonmycorrhizal and
endomycorrhizal root cells of tobacco (Genre and Bonfante 1997, 1998),
Asparagus (Matsubara et al. 1999), Medicago truncatula (Blancaflor et al.
2001), and in protocorms of orchid seeds (Uetake et al. 1997; Uetake and
Peterson 1997,1998). Protocorms develop at the base of germinating orchid
seeds and invasion of the parenchyma cells by a symbiotic fungus is necessary
for the further development of the embryo. Several common features were
observed in the reorganization of MT cytoskeleton in roots and protocorms
after invasion of the symbiotic fungus into the plant cells. In all three cases the
fungus invades differentiated parenchyma cells containing mainly transversely
orientated cortical (below the plasma membrane) MTs connected with
a few cytoplasmic MTs to the nucleus. After hyphal penetration, the plasma
membrane separating the fungal hyphae from the plant cell cytoplasm, the
perifungal membrane (Uetake and Peterson 1998), expands to follow the
branching of the fungal hyphae. The growth of the hyphae in the intracellular
space leads to formation of an arbuscule in endomycorrhiza and a peloton of
hyphal coils in orchid mycorrhiza. The hyphal growth is associated with profound
reorganization of MT cytoskeleton in the plant cell (Uetake et al. 1997;
Uetake and Peterson 1997; Genre and Bonfante 1997, 1998; Matsubara et al.
1999; Blancaflor et al. 2001). During fungal invasion the cortical MTs of the
plant cell disappear probably through depolymerization, and new MTs, less
well orientated, reappear at the plasma membrane surrounding the intracellular
hyphae.
The signals and mechanisms behind the observed reorganization of MT
cytoskeleton in plant cells colonized by endomycorrhizal fungi are not yet
known. However, it can be speculated that the invasion and proliferation of
fungal hyphae in the space between cell wall and plasma membrane of a dif-