Actin-binding proteins in plant cells

Actin occurs in all plant cells, as monomers, filaments and filament assemb lies. 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 t he preprophase band and phragmoplast and are indispensable for cell divisio n. Actin filaments continually polymerise and depolymerise from a pool of m onomers, and signal transduction pathways affecting cell morphogenesis modi fy the actin cytoskeleton. The interactions of actin monomers and filaments with actin-binding proteins (ABPs) control actin dynamics. By binding to a ctin monomers, ABPs, such as profilin, regulate the pool of monomers availa ble for polymerisation. By breaking filaments or capping filament ends, ABP s, such as actin depolymerising factor (ADF), prevent actin filament elonga tion or loss of monomers from filament ends. By bivalent cross-linking to a ctin filaments, ABPs, such as fimbrin and other members of the spectrin fam ily, produce a variety of higher order assemblies, from bundles to networks . The motor protein ABPs, which are not covered in this review, move organe lles along actin filaments. The large variety of ABPs share a number of fun ctional modules. A plant representative of ABPs with particular modules, an d therefore particular functions, is treated in this review.