PLANT PROFILINS RESCUE THE ABERRANT PHENOTYPE OF PROFILIN-DEFICIENT DICTYOSTELIUM CELLS

To characterize the function of plant profilins in vivo, we expressed two pollen-specific Zea mays (maize) profilin isoforms in profilin-min us Dictyostelium discoideum mutants. In maize, profilins exist as a mu ltigene family containing 4 or more members which are highly similar t o each other but substantially less similar to profilins from animals and lower eukaryotes. previously we have shown that D. discoideum prof ilin-minus cells have an aberrant phenotype due to defects in cell sha pe, cytokinesis, and development. These defects could be rescued by in troducing the pollen-specific profilins 1 or 2 from maize using a newl y constructed expression vector. Expression of the heterologous profil ins in Dictyostelium clones was assayed by affinity purification of th e pollen profilins with poly-L-proline agarose and by immunoblotting w ith a polyclonal antiserum raised against maize pollen profilin. In co ntrast to the profilin-minus mutants, Dictyostelium cells expressing p lant profilins showed normal cell shape, contained less F-actin, and w ere able to form fruiting bodies. These data provide genetic evidence that maize pollen profilins, even though they are specific for a disti nct developmental stage, share functional properties with profilin fro m a lower eukaryote and apparently act as G-actin-sequestering protein s in this system. (C) 1996 Wiley-Liss, Inc.