plant surface microbiology.pdf

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Marjatta Raudaskoski, Mika Tarkka and Sara Niini
TKRP125 is located in anaphase spindle and phragmoplast.A similar location
has been recently shown for a TKRP125 homologue and a KRP slightly deviating
from TKRP125 isolated from carrot tissue culture (Barroso et al. 2000).
In plants, a subfamily of kinesin-like genes encodes proteins with a calmodulin-binding
domain. Genes encoding members of this subfamily have been
isolated from Arabidopsis (AKCBP; Reddy et al. 1996a), potato (PKCBP; Reddy
et al. 1996b), and tobacco (TCK1; Wang et al. 1996). The genes encode minus
end-directed motor proteins with the calmodulin-binding region in the
motor domain at the very C-terminus of the polypeptide, suggesting that calcium/calmodulin
may be involved in the regulation of the microtubule-based
movements in plants. Genes encoding other types of minus end-directed
motor molecules are also present in Arabidopsis and they have been named
katA to katE (Mitsui et al. 1993, 1994). The production of minus end-directed
KatB and KatC kinesins increases during M-phase of the cell cycle in tobacco
BY-2 cell cultures, suggesting that mitotic spindle and phragmoplast may also
be their site of action (Mitsui et al. 1996). Dyneins are large minus enddirected
motors. Until now, no dynein heavy chain encoding gene has been
detected in expressed sequence tag (EST) databases from flowering plants or
in the recently sequenced Arabidopsis genome (Lawrence et al. 2002).
In endomycorrhiza, the organization of MT cytoskeleton changes when the
fungus colonizes the plant cell (Genre and Bonfante 1997). In addition, in P.
sylvestris ectomycorrhiza cortical cells surrounded by the Hartig net seem to
contain less cortical MTs than the noninfected cortical cells (Niini 1998). The
reorganization of the MT cytoskeleton takes place not only in the colonized
endomycorrhizal plant cells, but also in the cells adjacent to the colonized
ones, and when the arbuscules have completely collapsed, the transversely
oriented cortical MTs next to the plasma membrane reappear (Blancaflor et
al. 2001). The reorganization of the MT cytoskeleton observed in connection
with symbiosis requires destabilization (depolymerization) of existing cortical
MTs, polymerization of new MT areas at the plasma membrane next to the
colonizing fungus, and repolymerization of cortical MTs after the senescence
of the arbuscular structure. The observed changes present a very dynamic
behavior of MT cytoskeleton in endomycorrhiza, which probably involves the
function of both structural and motor MAPs in plant cells.
7.2 Fungal Hyphae
In filamentous fungi, the genes encoding MT-associated motor proteins
kinesins and dyneins have caught more attention than structural MAPs. The
first kinesin-related protein was cloned from ascomycete Aspergillus nidulans
(Enos and Morris 1990) as a temperature-sensitive mutation that blocked
mitosis in germinating conidia. Later studies have shown that this bimC
(blocked in mitosis) gene encodes a protein with amino-terminal motor and