Essential protein required during embryogenesis and pollen development (PubMed:23382868). Endonuclease cleaving pre-rRNA at the 3' end of the mature 18S rRNA (D-site); cleaves 20S pre-rRNA in the cytoplasm (PubMed:23382868). Required for processing of 20S pre-rRNA precursor and biogenesis of 40S ribosomal subunits (PubMed:23382868). Component of the small ribosomal subunit, ribosomal RNA processing complex (SSU RRP complex). Highly expressed in flowers and siliques and at lower levels in roots, hypocotyls, stems, leaves and seeds. Delayed pollen development with reduced nuclei content leading to reduced pollen germination capacity, and pale seeds with arrested embryo development at the globular stage in homozygous plants (PubMed:23382868). In heterozygous plants, strong accumulation of the 23S-like precursor P-A3, and moderate increased levels of 35S/33S precursors and 20S pre-rRNAs (PubMed:23382868). Alterated leaf morphology and inhibited inflorescence elongation leading to a loss of reproduction, seeds abortion and slightly reduced siliques size (PubMed:23382868). Belongs to the NOB1 family.