Arabidopsis E2FA stimulates proliferation and endocycle separately through RBR-bound and RBR-free complexes

• Published in: The EMBO journal 2012-03, Vol.31 (6), p.1480-1493
• Main Authors: Magyar, Zoltán, Horváth, Beatrix, Khan, Safina, Mohammed, Binish, Henriques, Rossana, De Veylder, Lieven, Bakó, László, Scheres, Ben, Bögre, László
• Format: Article
• Language: English
• Subjects: a-type cyclin; Arabidopsis; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Cell Differentiation - genetics; Cell Growth Processes - genetics; cell proliferation; Cellular biology; Chromatin - genetics; Chromatin - metabolism; cyclin-dependent kinase; Cyclins - genetics; Cyclins - metabolism; dna-replication; E2F; E2F Transcription Factors - genetics; E2F Transcription Factors - metabolism; EMBO06; EMBO30; endocycle; follicle cells; Gene Expression Regulation, Plant; genome-wide identification; leaf development; Leaves; Meristem - genetics; Meristem - metabolism; Mutation; Plant biology; plant development; Plant growth; Plant Leaves - genetics; Plant Leaves - metabolism; Plants, Genetically Modified - genetics; Plants, Genetically Modified - metabolism; Promoter Regions, Genetic; Protein Binding; Proteins; retinoblastoma; retinoblastoma-related protein; Roots; stem-cell maintenance; Sucrose - metabolism; transcription factor
• ISSN: 0261-4189; 1460-2075; 1460-2075
• DOI: 10.1038/emboj.2012.13

Post‐embryonic growth in plants depends on the continuous supply of undifferentiated cells within meristems. Proliferating cells maintain their competence for division by active repression of differentiation and the associated endocycle entry. We show by upregulation and downregulation of E2FA that it is required for maintaining proliferation, as well as for endocycle entry. While E2FB–RBR1 (retinoblastoma‐related protein 1) complexes are reduced after sucrose addition or at elevated CYCD3;1 levels, E2FA maintains a stable complex with RBR1 in proliferating cells. Chromatin immunoprecipitation shows that RBR1 binds in the proximity of E2F promoter elements in CCS52A1 and CSS52A2 genes, central regulators for the switch from proliferation to endocycles. Overexpression of a truncated E2FA mutant (E2FA ΔRB ) lacking the RBR1‐binding domain interferes with RBR1 recruitment to promoters through E2FA, leading to decreased meristem size in roots, premature cell expansion and hyperactivated endocycle in leaves. E2F target genes, including CCS52A1 and CCS52A2 , are upregulated in E2FA ΔRB and e2fa knockout lines. These data suggest that E2FA in complex with RBR1 forms a repressor complex in proliferating cells to inhibit premature differentiation and endocycle entry. Thus, E2FA regulates organ growth via two distinct, sequentially operating pathways. The transcription factor E2FA stimulates mutually exclusive plant cell‐cycle states, mitotic proliferation and differentiation‐associated endocycles. In complex with retinoblastoma protein RBR1, E2FA first maintains proliferation by repressing differentiation genes, while later acting independently to promote endocycle entry.