plant surface microbiology.pdf

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Marjatta Raudaskoski, Mika Tarkka and Sara Niini
solin-like headpiece, villin may also act as an actin-severing protein, although
this activity has not yet been demonstrated for plant villins.
In Arabidopsis, 17 myosin encoding genes have been identified, which on
the basis of phylogenetic analysis, fall into plant-specific myosin classes VIII
(4 genes) and XI (13 genes). The three cloned myosins from maize and four
from Helianthus annuus also fall into these classes (Reddy and Day 2001). The
true structure, enzymatic properties, intracellular localization and physiology
of plant myosin are not yet known.
The structure and function of actin binding proteins in association with
the reorganization of the actin cytoskeleton in plant cells at mycorrhiza formation
has not yet been studied, but seems to require attention. In endomycorrhiza,
rearrangement of actin cytoskeleton was observed at the colonization
of tobacco cortical cells by endomycorrhizal fungus (Genre and Bonfante
1997). Actin cables, typical for noncolonized cortical root cells, disappeared
and MF polymerized to a network at the plasma membrane surrounding the
arbuscule branches. The observed changes may be hypothesized to require
both the activation and function of proteins involved in the reorganization of
the actin cytoskeleton as a consequence of the perception of signals from the
intruding fungus.
The research on actin binding proteins in filamentous fungi seems to be
restricted to myosin (McGoldrick et al. 1995), in Aspergillus nidulans and to
actin-related proteins Arp1 (Plamann et al. 1994) in Neurospora crassa,
although in yeast, Saccharomyces cerevisiae, most actin binding proteins previously
described in plants are present and have been studied in detail
(Ayscough 1998). In A. nidulans, the myosin I encoding gene myoA has been
cloned and different mutational studies have indicated that MYOA is necessary
for the maintenance of polarized growth, secretion and endocytosis
(McGoldrick et al. 1995; Osherov et al. 1998; Yamashita and May 1998). The
yeast S. cerevisiae and Schizosaccharomyces pombe, similar to animal cells,
contain myosins from classes II and V in addition to those belonging to class
I which predicts that additional myosins will be detected in future from filamentous
fungi.
7 Microtubule-Associated Proteins
7.1 Plant Cells
Microtubule-associated proteins (MAPs) are divided into structural and
motor proteins. Several genes encoding structural plant MAPs have been isolated
in the last few years. One of the MAP encoding genes was isolated from
Arabidopsis, where its heat-sensitive mutation resulted in the disintegration of
cortical microtubules in leaf, hypocotyl and root cells. The gene was named