Essential protein required during embryogenesis and pollen development (PubMed:23382868). Required for processing of 20S pre-rRNA precursor and biogenesis of 40S ribosomal subunits (PubMed:23382868). Component of the 40S pre-ribosome. Highly expressed in flowers and at lower levels in roots, hypocotyls, stems, leaves, siliques 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, slight accumulation of the 23S-like precursor P-A3 (PubMed:23382868). Reduced siliques size with small non-developed and early aborted seeds (PubMed:23382868). Belongs to the bystin family.