Acts as a regulatory subunit of the 26 proteasome which is involved in the ATP-dependent degradation of ubiquitinated proteins (By similarity). Required during embryogenesis (PubMed:16169895). Required for optimal plant growth and stress responses (PubMed:19605416). Required for innate immunity (PubMed:22577987). Prevents JMJ27 accumulation in non-drought conditions (PubMed:34197643). Component of the 19S regulatory particle (RP/PA700) base subcomplex of the 26S proteasome. The 26S proteasome is composed of a core protease (CP), known as the 20S proteasome, capped at one or both ends by the 19S regulatory particle (RP/PA700). The RP/PA700 complex is composed of at least 17 different subunits in two subcomplexes, the base and the lid, which form the portions proximal and distal to the 20S proteolytic core, respectively. Interacts with JMJ27 (PubMed:34197643). Expressed in stems, leaves, buds, flowers, siliques and developing seeds. Detected in the floral meristem and primordia of floral organs. During early stages of flower development, expressed in the whole floral meristem, especially in emerging primordia. Later present in developing carpels, particularly in emerging ovule primordia. After fertilization, observed in the embryo and the chalazal endosperm. High levels at the early embryogenesis stages that fade out later. Also present in the developing seed coat, the septum, and the silique wall. In the stamens, detected at high levels in the anthers. Observed in sporogenous cells and then in tetrads of microspores. By salicylic acid (SA) (PubMed:22577987). Repressed by drought (PubMed:34197643). Embryo lethality due to development arrest at the globular stage with defects in the formation of the embryonic root, the protoderm, and procambium (PubMed:16169895). Increased cell sizes, anthocyanin accumulation, reduced growth rate, reduced fertility, decreased heat shock tolerance, increased oxidative stress tolerance (PubMed:19605416). Mutant displays enhanced susceptibility to the fungal pathogen G. cichoracearum and to virulent and avirulent bacterial Pto DC3000 strains, which indicated defects in basal defense and resistance (R) protein-mediated defense (PubMed:22577987). Belongs to the proteasome subunit S2 family. The embryo lethal disruption phenotype (PubMed:16169895) could be confirmed (PubMed:19605416). Truncated N-terminus.