The 26S protease is involved in the ATP-dependent degradation of ubiquitinated proteins. The regulatory (or ATPase) complex confers ATP dependency and substrate specificity to the 26S complex (PubMed:22158466) (Probable). Interacts with transit peptides of proteins targeted to the chloroplast, and may be involved in the degradation of unimported plastid protein precursors (PubMed:24846764). Is required for the maintenance of postembryonic root and shoot meristems (PubMed:15073153, PubMed:21784786). Has a specific role in the regulation of organs size (PubMed:19500299, PubMed:19321709). Acts redundantly with RPT2B in the regulation of gametogenesis (PubMed:21784786, PubMed:22158466). With RPT2B plays a critical role in 26S proteasome assembly (PubMed:22158466). Acts as an upstream signaling component for inducing both defense and morphological phenotypes in the constitutive active uni-1D mutant (PubMed:21791544). Acts as negative regulator of endoreduplication in trichome cells (PubMed:20195883). May function after the completion of the third endoreduplication step (8C to 16C) mediated by RHL1 (PubMed:20195883). Acts as negative regulator of transcriptional gene silencing (TGS) at specific endogenous genes through DNA methylation (PubMed:22615900). Promotes post-transcriptional gene silencing (PTGS) by limiting the degradation of transgene aberrant RNAs by the RNA quality control (RQC) machinery, thus favoring their entry into cytoplasmic siRNA bodies where they can trigger PTGS (PubMed:22615900). Involved in tolerance to zinc deficiency, possibly through alleviation of oxidative stresses or processing of poly-ubiquitinated proteins (PubMed:21389614). Required for resistance to the fungal pathogen Golovinomyces cichoracearum (PubMed:22577987). 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. Required for innate immunity (PubMed:14623884, PubMed:20516081). Interacts with UNI (PubMed:21791544). Localizes to siRNA-bodies in the cytoplasm. Preferentially expressed in the root and shoot apical meristem. Induced by treatment with the proteasome inhibitor MG132. Displays disruption of cellular organization in the postembryonic root and shoot apical meristems. Leads to decreased 26SP accumulation, resulting in reduced rates of Ub-dependent proteolysis. Shows hypersensitivity to heat shock and increased oxidative stress tolerance. Displays enlarged leaves, stems, flowers, fruits, seeds and embryos, caused by increased cell size and shows increased branch number and nuclear size of trichomes, in correlation with increased ploidy. Mutant displays enhanced susceptibility to the fungal pathogen Golovinomyces cichoracearum. The double mutants rpt2a and rpt2b are blocked in both male and female gametogenesis (PubMed:22158466, PubMed:21784786). Belongs to the AAA ATPase family.