Acts redundantly with DA1 and DAR1 to regulate endoreduplication during leaf development. Together with DA1 and DAR1, modulates the protein stability of the transcription factors TCP14 and TCP15, which repress endoreduplication by directly regulating the expression of cell-cycle genes (PubMed:25757472). Involved in root phloem development. Is an essential component of early phloem development, long-distance delivery of phloem content, and proper maintenance of root system architecture (PubMed:21749503). Involved in the control of root meristem size. Functions genetically downstream of cytokinin and IAA3 to maintain normal auxin distribution by influencing polar auxin transport. Acts through the PLETHORA pathway, upstream of PLT1 and PLT2 to influence root stem cell niche activity and thus control root meristem size (PubMed:23296689). Interacts with ubiquitin, TCP14 and TCP15. Expressed in the vasculature of leaves, inflorescence stems, flowers, hypocotyls, and primary and lateral roots. In roots, expressed in phloem companion cells. 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. Reduced primary root growth, increased lateral root formation, and altered root system architecture, due to altered early phloem development. Exogenous treatment with auxin rescues the phloem defects of the lrd3 knockout mutant.