Poster: Cytoskeleton: Structure & Function

Abs # 1123: The Arabidopsis Actin-Related Proteins AtARP4 and AtARP7 are Essential for Embryo Development

Presenter:	Kandasamy, Muthugapatti K, kandu@arches.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 about 20 to 60% sequence homology and the 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 suggested to be involved in chromatin remodeling, hence may effect transcriptional regulation and DNA repair. We found that AtARP4, a homolog of human BAF53 and yeast Arp4, and AtARP7, a novel plant-specific ARP, are localized to the nucleus in a cell cycle dependent manner. In interphase cells, both AtARP4 and AtARP7 proteins are concentrated in the nucleus, whereas in mitotic cells they are excluded from the chromosomes and dispersed throughout the cytoplasm in all the organs and tissues. To gain insight in to the role of these two ubiquitously expressed ARPs in plants, we have isolated T-DNA insertion mutants and generated RNAi suppression lines that are partially or completely defective in the expression of these proteins. Phenotypic and genetic analyses of ARP4-3 and ARP7-1 mutants, which have T-DNA insertion in the first intron and exon respectively, revealed aberrant embryo development and homozygous lethality. Partial reduction in the level of AtARP4 protein in the ARP4-1 mutant and RNAi lines resulted in sterility and severe defects in flower and silique development. We suggest that both AtARP4 and AtARP7 are essential for embryo morphogenesis and Arabidopsis plant development. Based on our results and data on the ortholog of AtARP4 in yeast and other organisms, we are considering possible roles for these two ARPs in chromatin remodeling-related transcriptional regulation in plants.