The Arabidopsis thaliana SNF2 homolog AtBRM controls shoot development and flowering

Chromatin remodeling is essential for the reprogramming of transcription associated with development and cell differentiation. The SWI/SNF complex was the first chromatin remodeling complex characterized in yeast and Drosophila. In this work we have characterized an Arabidopsis thaliana homolog of Brahma, the ATPase of the Drosophila SWI/SNF complex. As its Drosophila counterpart, Arabidopsis thaliana BRAHMA (AtBRM) is a nuclear protein present in a high molecular mass complex. Furthermore, the N terminus of AtBRM interacts, in the two-hybrid system, with CHB4 (AtSWI3C), an Arabidopsis homolog of the yeast SWI/SNF complex subunit SWI3. The AtBRM gene is primarily expressed in meristems, organ primordia and tissues with active cell division. Silencing of the expression of the AtBRM gene by RNA interference demonstrated that AtBRM is required for vegetative and reproductive development. The AtBRM silenced plants exhibited a reduction in overall plant size with small and curled leafs, as well as a reduction in the size of the inflorescence meristem. In the absence of AtBRM, Arabidopsis flowers have small petals and stamens, immature anthers, homeotic transformations and reduced fertility. The AtBRM silenced plants flower earlier than wild-type plants both under inductive and non-inductive photoperiods. Furthermore, levels of CO, FT and SOC1 transcripts were up-regulated under non-inductive conditions suggesting that AtBRM is a repressor of the photoperiod-dependent flowering pathway.