Profilin plays a role in cell elongation, cell shape maintenance, and flowering in arabidopsis

Profilin (PFN) is an ubiquitous, low-M-r, actin-binding protein involved in the organization of the cytoskeleton of eukaryotes including higher plants . PFNs are encoded by a multigene family in Arabidopsis. We have analyzed i n vivo functions of Arabidopsis PFN by generating transgenic plants carryin g a 35S-PFN-1 or 35S-antisense PFN-1 transgene. Etiolated seedlings underex pressing PFN (PFN-U) displayed an overall dwarf phenotype with short hypoco tyls whose lengths were 20% to 25% that of wild type (WT) at low temperatur es. Light-grown PFN-U plants were smaller in stature and flowered early. Co mpared with equivalent cells in WT, most cells in PFN-U hypocotyls and root s were shorter, but more isodiametric, and microscopic observations of etio lated PFN-U hypocotyls revealed a rough epidermal surface. In contrast, lig ht-grown seedlings overexpressing PFN had longer roots and root hair althou gh etiolated seedlings overexpressing PFN were either the same size or slig htly longer than WT seedlings. Transgenic seedlings harboring a PFN-1-GUS t ransgene directed expression in root and root hair and in a ring of cells a t the elongating zone of the root tip. As the seedlings matured PFN-1-GUS w as mainly expressed in the vascular bundles of cotyledons and leaves. Our r esults show that Arabidopsis PFNs play a role in cell elongation, cell shap e maintenance, polarized growth of root hair, and unexpectedly, in determin ation of flowering time.