Poster: Cytoskeleton structure & dynamics

Abs # 679: Knocking down the nuclear actin-related protein AtARP4 induces early flowering and delays senescence of the perianth in Arabidopsis

Presenter:	Kandasamy, Muthugapatti K, kandu@uga.edu
Authors	Kandasamy, Muthugapatti K (A)   Deal, Roger B (A)   McKinney, Elizabeth C (A)   Meagher, Richard B (A)
Affiliations:	(A): University of Georgia

Actin-related proteins (ARPs), which share moderate sequence homology and basal structure with conventional actins, are found in a wide variety of organisms, including plants. While their functions are not clear, several ARPs are localized to the nucleus and are identified as components of various chromatin-modifying complexes that are involved in transcriptional regulation. We found that AtARP4, a homolog of human BAF53 and yeast Arp4, is concentrated in the nucleus of all Arabidopsis tissues. In addition, the orthologs of AtARP4 in Brassica and tobacco are associated with the nucleus. To gain insight into the role of ARP4 in plants, we have isolated a T-DNA insertion mutant line and generated RNAi suppression lines in Arabidopsis. Phenotypic and genetic analyses of the arp4-1 mutant, which has a T-DNA insertion in the promoter region and a moderate reduction in the level of AtARP4 protein expression, revealed partial sterility, and defects in anther and pollen development. Targeting the distinct 3ŽUTR of AtARP4 transcripts in RNAi plants caused a drastic reduction in the level of AtARP4 protein expression, and resulted in early flowering under long-day photoperiods and delayed senescence of the perianth. Moreover, ARP4-RNAi expression induced pleiotropic effects such as reduced plant size and fertility, and altered organization of plant organs. Immunolabeling demonstrated a clear correlation between reductions in the level of ARP4 protein expression in the nucleus and severity of the phenotypes. Based on our results and data on the ortholog of AtARP4 in yeast and other organisms, we suggest that AtARP4 protein has possible roles in chromatin remodeling that mediates global changes in plant gene regulation.