The B regulatory subunit may modulate substrate selectivity and catalytic activity, and also may direct the localization of the catalytic enzyme to a particular subcellular compartment (By similarity). Associates with the serine/threonine-protein phosphatase PP2A catalytic subunit C and regulatory subunit A to positively regulates beta-oxidation of fatty acids and protoauxins in peroxisomes by dephosphorylating peroxisomal beta-oxidation-related proteins (PubMed:25489022). Required for the formation of the PP2A holoenzyme that negatively regulates brassinosteroid signaling by dephosphorylating and inactivating BRI1 in the cytoplasm (PubMed:26517938). PP2A consists of a common heteromeric enzyme, composed of a catalytic subunit (subunits C), a constant regulatory subunit (subunit A), and a variety of regulatory subunits such as subunits B (the R2/B/PR55/B55, R3/B''/PR72/PR130/PR59 and R5/B'/B56 families) (By similarity). Interacts with BZR1 (PubMed:21258370). Interacts with PP2A2, PP2A5 and PP2AA2 (PubMed:25489022). Highly expressed in dry seeds. Expressed in roots, cotyledons, rosette leaves and flowers. Induced by epibrassinolide. Reduced plant size and fresh weight. Belongs to the phosphatase 2A regulatory subunit B56 family.