Pollen specific expression of maize genes encoding actin depolymerizing factor-like proteins.

Abstract

In pollen development, a dramatic reorganization of the actin cytoskeleton takes place during the passage of the pollen grain into dormancy and on activation of pollen tube growth. A identical to ZmABPI and ZmABP2, respectively, and its expression is suppressed in pollen and germinated pollen. The fundamental biochemical characteristics of the ZmABP proteins has been elucidated using bacterially expressed ZmABP3 protein. This has the ability to bind monomeric actin (G-actin) and filamentous actin (F-actin). Moreover, it decreases the viscosity of polymerized actin solutions consistent with an ability to depolymerize filaments. These biochemical characteristics, taken together with the sequence comparisons, support the inclusion of the ZmABP proteins in the ADF group.

F-actin and G-actin binding are uncoupled by mutation of conserved tyrosine residues in maize actin depolymerizing factor (ZmADF)

“…As pollen grains enter dormancy, F-actin is condensed into spiculate aggregates; during pollen germination and tube growth these are replaced by a microfilament array that is required for tip growth (4)(5)(6). The identification in pollen grains of specifically expressed isogenes of plant profilin and actin depolymerizing factor has led to the suggestion that these proteins may be specifically involved in the dynamics of this actin reorganization (7)(8)(9). Both the plant profilins and the plant actin depolymerizing factors have been shown to function in vitro in a manner similar to their animal and fungal counterparts (8)(9)(10).…”

“…The identification in pollen grains of specifically expressed isogenes of plant profilin and actin depolymerizing factor has led to the suggestion that these proteins may be specifically involved in the dynamics of this actin reorganization (7)(8)(9). Both the plant profilins and the plant actin depolymerizing factors have been shown to function in vitro in a manner similar to their animal and fungal counterparts (8)(9)(10).…”

“…9 and 20) interact with both monomeric and filamentous actin, in vitro, and sever filaments (9,17,(21)(22)(23). The members of the ADF group show a high conservation of primary structure and function.…”

“…Competition studies using a synthetic heptapeptide patterned on the sequence Asp-122 to Leu-128 suggest that this region may also constitute part of the actin binding domain (31). These actin and PIP 2 binding regions are highly conserved in the equivalent plant ADF sequences (9). The tertiary structures of destrin, yeast cofilin, and Acanthamoeba actophorin have recently been reported from nuclear magnetic resonance studies (32) and x-ray analysis (33,34).…”

Soluble expression and characterization of a GFP-fused pea actin isoform (PEAc1)

“…Although some methods have been developed to get relatively high yields of actin from plant pollens [24,25], it is still very difficult to purify actin (especially actin isoforms) from most of the plants [26]. Expression of proteins in E. coli has greatly facilitated our understanding of physicochemical properties of proteins including plant actin binding protein [27,28]. Unfortunately, there is still no successful example of the expression of active eukaryotic actin in E. coli.…”