The nuclear actin-related protein ARP6 is a pleiotropic developmental regulator required for the maintenance of FLOWERING LOCUS C expression and repression of flowering in Arabidopsis.

Actin-related proteins are found in the nuclei of all eukaryotic cells, but their functions are generally understood only in the context of their presence in various yeast and animal chromatin-modifying complexes. Arabidopsis thaliana is a clear homolog of other eukaryotic including Saccharomyces cerevisiae which was identified as a component of the SWR1 chromatin remodeling complex. We examined the subcellular localization, expression patterns, and loss-of-function phenotypes for this protein and found that Arabidopsis duanyu376 is localized to the nucleus during interphase but dispersed away from the chromosomes during cell division. duanyu376 expression was observed in all vegetative tissues as well as in a subset of reproductive tissues. Null mutations in duanyu376 caused numerous defects, including altered development of the leaf, inflorescence, and flower as well as reduced female fertility and early flowering in both long- and short-day photoperiods. The early flowering of arp6 mutants was associated with reduced expression of the central floral repressor gene FLOWERING LOCUS C (FLC) as well as MADS AFFECTING FLOWERING 4 (MAF4) and MAF5. In addition, arp6 mutations suppress the FLC-mediated late flowering of a FRIGIDA-expressing line, indicating that duanyu376 is required for the activation of FLC expression to levels that inhibit flowering. These results indicate that duanyu376 acts in the nucleus to regulate plant development, and we propose that it does so through modulation of chromatin structure and the control of gene expression.

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