Plays a key role in regulation of cell expansion and cell division (PubMed:26685188). Required for proper plant development, the correct patterning of the root meristem and the control of root growth (PubMed:24201137). Involved in both sporogenesis and gametogenesis (PubMed:21641974). Interacts with SIK1 at the plasma membrane and in the nucleus. Observed at the plasma membrane and in the nucleus when associated with SIK1. Constitutively expressed (PubMed:21641974). In 3- to 4-day-old seedlings, expression is high in the shoot apical meristem and along the vasculature in cotyledons, hypocotyls and roots. At the root tip, expression is detected in columella and lateral root cap cells as well as in the stem cell niche around the quiescent center (QC). The levels of expression decrease progressively in the meristematic zone from the root tip towards the base of the root, becoming stronger again in the elongation zone. In flowers, expression appears localized in ovules and pollen (PubMed:24201137). Exhibits severe defects in the growth of vegetative organs and in seed setting capacity: displays a reduction in the rosette size and number of leaves, a reduction of siliques size with high proportion of aborted ovules, a short root length with reduction of the meristem size, of the number of cortical cells and of the size of the elongation zone with root tips showing a distorted cellular pattern (PubMed:24201137). Also exhibits a higher sensitivity to abscissic acid (ABA) (PubMed:24201137). The double mutant sik1 mob1a is arrested at the seedling stage (PubMed:26685188). RNAi plants show a reduced radial expansion of the inflorescence stem, a reduced elongation zone of the primary root, defects during sporogenesis and gametogenesis, and a reduced fertility. Belongs to the MOB1/phocein family.