Profilin Plays a Role in Cell Elongation, Cell Shape Maintenance, and Flowering in Arabidopsis

Abstract

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 in vivo functions of Arabidopsis PFN by generating transgenic plants carrying a 35S-PFN-1 or 35S-antisense PFN-1 transgene. Etiolated seedlings underexpressing PFN (PFN-U) displayed an overall dwarf phenotype with short hypocotyls whose lengths were 20% to 25% that of wild type (WT) at low temperatures. Light-grown PFN-U plants were smaller in stature and flowered early. Compared with equivalent cells in WT, most cells in PFN-U hypocotyls and roots were shorter, but more isodiametric, and microscopic observations of etiolated PFN-U hypocotyls revealed a rough epidermal surface. In contrast, light-grown seedlings overexpressing PFN had longer roots and root hair although etiolated seedlings overexpressing PFN were either the same size or slightly longer than WT seedlings. Transgenic seedlings harboring a PFN-1-GUS transgene directed expression in root and root hair and in a ring of cells at the elongating zone of the root tip. As the seedlings matured PFN-1-GUS was mainly expressed in the vascular bundles of cotyledons and leaves. Our results show that Arabidopsis PFNs play a role in cell elongation, cell shape maintenance, polarized growth of root hair, and unexpectedly, in determination of flowering time.

A Class I ADP-Ribosylation Factor GTPase-Activating Protein Is Critical for Maintaining Directional Root Hair Growth in Arabidopsis

“…Actin-disrupting drugs inhibited or delocalized root hair growth (Bibikova et al, 1999;Ketelaar et al, 2003), consistent with reports showing that knockouts to the vegetative ACT2 gene in Arabidopsis have distorted root hair morphology (Ringli et al, 2002). Moreover, altering the expression of genes encoding proteins that affect actin turnover, such as profilin, actin-depolymering factor, formin, actininteracting protein, and cyclase-associated protein, disrupted normal root hair development (Ramachandran et al, 2000;Dong et al, 2001;Yi et al, 2005;Deeks et al, 2007;Ketelaar et al, 2007).…”

Actin Interacting Protein1 and Actin Depolymerizing Factor Drive Rapid Actin Dynamics inPhyscomitrella patens

“…Indeed genetic studies support the requirement for a number of actin binding proteins in the expansion of tip-growing cells . These include actin-nucleating proteins, such as formins (Vidali et al, 2009c;Ye et al, 2009;Cheung et al, 2010) and the Arp2/3 complex (Harries et al, 2005;Perroud and Quatrano, 2006;Finka et al, 2008), the filament-stabilizing fimbrins , actin monomer binding proteins like profilin (Ramachandran et al, 2000;Vidali et al, 2007Vidali et al, , 2009b, and actin turnover proteins like actin depolymerizing factor (ADF) (Augustine et al, 2008;Vidali et al, 2009b), villin Zhang et al, 2011), and actin interacting protein1 (AIP1) (Ketelaar et al, 2004). It is tempting to suggest that these actin binding proteins are important for tip growth by promoting the reorganization of F-actin.…”

Directional cell expansion — turning toward actin

“…Traditionally, microtubules have been implicated in the direction of expansion, probably by orienting newly synthesized cellulose microfibrils [1,2]. By contrast, actin has been implicated in the rate (or overall extent) of expansion [3][4][5][6], probably through delivery of Golgi vesicles that contain membrane and wall materials to the site of growth. This traditional distinction is well illustrated by tip-growing cells, such as pollen tubes.…”