Involved in nucleolar processing of pre-18S ribosomal RNA. Plays a role early in ribosome biogenesis, especially in the maturation of 5.8S rRNA (PubMed:23382868). Required for guard cell functions (PubMed:23185391). Component of the ribosomal small subunit (SSU) processome (By similarity). Interacts with TBP1 in the nucleus (PubMed:19929880). Expressed constitutively and ubiquitously; observed in seeds, seedlings, roots, leaves, stems, flowers and siliques. Induced by sucrose in guard cells. Impaired maturation of 5.8S rRNA, especially the processing at the 5' end. Reduced siliques size due to defects in embryo and female gametophyte development (PubMed:23382868). Defects in guard cell function leading to reduced stomatal conductance and impaired water-use efficiency (PubMed:23185391). Belongs to the WD repeat PWP2 family.