Abstract
Actin occurs in all plant cells, as monomers, filaments and filament assemblies. In
interphase, actin filaments form a cortical network, co-align with cortical microtubules,
and extend throughout the cytoplasm functioning in cytoplasmic streaming. During mitosis,
they co-align with microtubules in the preprophase band and phragmoplast and are indispensable
for cell division. Actin filaments continually polymerise and depolymerise from a
pool of monomers, and signal transduction pathways affecting cell morphogenesis modify
the actin cytoskeleton. The interactions of actin monomers and filaments with actin-binding
proteins (ABPs) control actin dynamics. By binding to actin monomers, ABPs, such as
profilin, regulate the pool of monomers available for polymerisation. By breaking
filaments or capping filament ends, ABPs, such as actin depolymerising factor (ADF),
prevent actin filament elongation or loss of monomers from filament ends. By bivalent
cross-linking to actin filaments, ABPs, such as fimbrin and other members of the spectrin
family, produce a variety of higher order assemblies, from bundles to networks. The
motor protein ABPs, which are not covered in this review, move organelles along actin
filaments. The large variety of ABPs share a number of functional modules. A plant
representative of ABPs with particular modules, and therefore particular functions,
is treated in this review.
Key Words
Actin-binding proteins - ADF/cofilin - cytoskeleton - fimbrin - plant cells - profilin
- spectrin
