Transcriptional repressor regulating endoreduplication through control of A-type cyclins expression (PubMed:17012601). Does not bind to promoter sequences (in vitro) and may act by interacting with tissue-specific transcription factors (PubMed:17012601). Enhances the endocycle in endoreduplicating cells in seedlings (PubMed:17012601). Required for efficient splicing (PubMed:25568310). Interacts with STIPL1/NTR1 (PubMed:25568310). Gradual reduction of expression as the first leaf develops. 90% reduction of expression at day 20 after imbibition. The C-terminal region (474-908) is responsible for the repressor activity. Reduction of polyploidy and inhibition of hypocotyl elongation. Belongs to the GCF family.