Acts redundantly with DA1 and DAR2 to regulate endoreduplication during leaf development. Together with DA1 and DAR2, modulates the protein stability of the transcription factors TCP14 and TCP15, which repress endoreduplication by directly regulating the expression of cell-cycle genes. Interacts with ubiquitin, TCP14 and TCP15. Highly expressed during early stages leaf development, and expression decreases at the later stages of leaf development. The UIM domains bind molecules modified by monoubiquitin or ubiquitin chains and promote coupled monoubiquitination. Polyubiquitinated by DA2. No visible phenotype.