Binds RNA. Associates with 28S, 18S and 5.8S mature rRNAs, several rRNA precursors and probably U3 small nucleolar RNA. May be involved in regulation of intermediate and late steps of rRNA processing. May be involved in ribosome assembly (By similarity). Required for expression of cell cycle genes such as CYCD3-1, RNR2A and CDKB1-1. Promotes, in a dose- and auxin-dependent manner, organ growth by stimulating both cell proliferation and expansion, via the regulation of RBR1 levels (PubMed:17024182). Component of a ribonucleoprotein complex (By similarity). Interacts with REIL1 AND REIL2 (PubMed:24603461). Strongly expressed in calls, roots and flowers, to a lower extent, in stems and siliques, but hardly detectable in leaves. Accumulates mostly in developing organs. During early stages of organ development, promotes cell proliferation, influences cell-size threshold for division and shortens the period of meristematic activity. In postmitotic cells, enhances cell expansion. Cell-cycle regulated expression with accumulation during the G1-to-S phase (PubMed:15689342). Accumulates in response to auxin. Expression levels correlate with genes involved in ribosome biogenesis and function (PubMed:17024182). Distorted reduced growth leading to small plants, and impaired fertility. At the seedling stage, a delay in leaf initiation and distorted leaf shape were characteristic of the silenced lines. Belongs to the peptidase M24 family.