Christopher Staiger
Christopher J. Staiger
Associate Professor; Ph.D., California, Berkeley, 1990

A remarkable example of cellular morpho- genesis, pollen tube growth, is essential for plant reproduction. In order to deliver non-motile sperm to the embryo sac, the vegetative cell of the pollen grain forms a tip-growing protuberance that extends at rates up to 1 cm/h. A dynamic network of filaments and associated proteins, the actin cytoskeleton, organizes the pollen cytoplasm, provides the molecular railroad tracks for cytoplasmic streaming, and orchestrates the delivery of secretory vesicles to the growing apex. The organization and function of the actin cytoskeleton depends upon coordinated polymerization and depolymerization of actin filaments, as well as the regulated formation of higher-order structures from these polymers. We have identified and characterized several plant actin-binding proteins (ABPs) that are likely to be key regulators of actin function, such as gene families for the actin monomer-binding protein profilin, and for the filament crosslinking protein fimbrin.

We are also using the recently completed Arabidopsis genome to perform a high-throughput functional proteomic analysis of a large collection of known and novel ABPs. By studying the ability of these proteins to bind actin in vitro and analyzing their effects on actin organization in living cells, we hope to gain further insight into how they might regulate cytoskeletal organization and signaling events during pollen development.

Figure: A pair of Tradescantia stamen hair cells which are stained with fluorescent-phalloidin to visualize microfilaments. The lower cell shows the normal microfilament array. The upper cell demonstrates the effect of introducing an excess of the actin-binding protein ADF1 on actin organization.

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