Fig. 1. atbrm mutants isolated in a genetic screen for phenotypic enhancers of cuc2-1. (A-F) 10-day-old cuc2-1 (A) or atbrm-1 (B) seedlings have well separated cotyledons. By contrast, cuc2-1 atbrm-1 double mutants exhibit cotyledon separation defects ranging from very strong (D) to moderate (E). cuc2-1 atbrm-3 also shows strong cotyledon separation defects (F). The strong cotyledon fusion (D,F) resembles that of cuc1-1 cuc2-1 double mutants (C). Genotypes are indicated in each panel. The cotyledons in cuc2-1 are labeled as `c' (A) to distinguish them from the primary leaves that form between the cotyledons. The outermost border of each fusion event is indicated by red arrowheads (D-F). Scale bars: 2 mm. (G) Mapping and cloning of the atbrm mutants. Asterisks indicate the position of CAPS markers used for fine mapping of the mutation in the H48 line. Arrows indicate predicted genes. The gene structure of AtBRM is represented by boxes for exons and by lines for untranslated regions and introns. (H) Molecular defects of the three atbrm alleles we identified. Structural domains of the protein are indicated: I, domain 1; II, domain 2; ATPase, SNF2 ATPase domain; purple oval, AT-hook; BM, bromodomain (e.g. Farrona et al., 2004).