The Arabidopsis BRAHMA Chromatin-Remodeling ATPase Is Involved in Repression of Seed Maturation Genes in Leaves    

Abstract

Synthesis and accumulation of seed storage proteins (SSPs) is an important aspect of the seed maturation program. Genes encoding SSPs are specifically and highly expressed in the seed during maturation. However, the mechanisms that repress the expression of these genes in leaf tissue are not well understood. To gain insight into the repression mechanisms, we performed a genetic screen for mutants that express SSPs in leaves. Here, we show that mutations affecting BRAHMA (BRM), a SNF2 chromatin-remodeling ATPase, cause ectopic expression of a subset of SSPs and other embryogenesis-related genes in leaf tissue. Consistent with the notion that such SNF2-like ATPases form protein complexes in vivo, we observed similar phenotypes for mutations of AtSWI3C, a BRM-interacting partner, and BSH, a SNF5 homolog and essential SWI/SNF subunit. Chromatin immunoprecipitation experiments show that BRM is recruited to the promoters of a number of embryogenesis genes in wild-type leaves, including the 2S genes, expressed in brm leaves. Consistent with its role in nucleosome remodeling, BRM appears to affect the chromatin structure of the At2S2 promoter. Thus, the BRM-containing chromatin-remodeling ATPase complex involved in many aspects of plant development mediates the repression of SSPs in leaf tissue.

Genetic analysis of functional redundancy of BRM ATPase and ATSWI3C subunits of Arabidopsis SWI/SNF chromatin remodelling complexes

“…These alleles correspond to nonsense mutations that presumably permit the synthesis of truncated protein products lacking various domains important for the biological function of BRM ). The brm-5 point mutation results in the exchange of Gly to Arg in the catalytic domain of BRM protein (Tang et al 2008). We have compared brm-6 (identiWed in this study) and the published phenotypic analyses of all aforementioned mutant lines and found that the brm-1, -2, -4 and -6 insertion mutations and brm-101, -102 and -103 point mutations resulted in the manifestation of all highly reproducible brm phenotypic traits described above.…”

“…We have compared brm-6 (identiWed in this study) and the published phenotypic analyses of all aforementioned mutant lines and found that the brm-1, -2, -4 and -6 insertion mutations and brm-101, -102 and -103 point mutations resulted in the manifestation of all highly reproducible brm phenotypic traits described above. The brm-3 and brm-5 mutants displayed less severe developmental alterations showing intermediate elongation and growth defects compared with wild-type and brm null mutant plants (Hurtado et al 2006;Tang et al 2008).…”

“…A portion of anti-BRM antibody was subsequently puriWed by aYnity chromatography (Eurogentec). For Western-blot analysis of the BRM protein, 30-day-old Col-0, brm-1, and -2, -3, and -4 and point mutations brm-101, -102, -103, and brm-5 were characterised previously (Hurtado et al 2006;Kwon et al 2006;Farrona et al 2007;Tang et al 2008). The brm-1 and brm-6 mutations were used in the genetic analyses described in this work.…”

“…The brm-1 (SALK-030046) and brm-2 (GABI-kat-854D01) insertion mutations were originally identiWed by Hurtado et al (2006). Similar to brm-4 (WiscDs/Lox436E9), which carries a transposon insertion (Tang et al 2008), both brm-1 and brm-2 were shown to represent null mutations. In contrast, the brm-3 (SALK-088462) insertion mutant expresses a truncated BRM protein that lacks a C-terminal segment of 454 amino acids encompassing the bromodomain motif (Farrona et al 2007).…”

“…Functional studies of Snf2-type ATPases showed that the Arabidopsis syd mutant is viable and its phenotypic characteristics are clearly diVerent from those of atswi3c and atswi3d mutants (Wagner and Meyerowitz 2002;Su et al 2006). In contrast, phenotypic traits of brm and atswi3c insertion mutants are intriguingly similar (Sarnowski et al 2005;Hurtado et al 2006;Tang et al 2008). The interaction of ATSWI3C with BRM in the yeast two-hybrid system (Farrona et al 2004) suggests that ATSWI3C is a core subunit of a BRM ATPase-associated SWI/SNF complex.…”