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). Required for the formation of the PP2A holoenzyme that negatively regulates brassinosteroid signaling by dephosphorylating and inactivating BRI1 in the cytoplasm (PubMed:26517938). Seems to be functionally connected with CPR5 and may mediate the negative regulation of defense reactions and senescence under low irradiances. May contribute to the epigenetic regulation of defense gene expression (PubMed:21571669). Involved in the control of methoxylation of indole glucosinolates and formation of 4-methoxy- indol-3-yl-methyl glucosinolate in leaves, through direct interaction with indole glucosinolate methyltransferases (PubMed:27598402). Involved in growth regulation and stress signaling (PubMed:26012558). Involved in the regulation of reactive oxygen species (ROS) signaling and maintenance of cellular ROS homeostasis (PubMed:26012558, PubMed:25307043). Required to control the level of ACO3 phosphorylation in the cytoplasm. Regulates hydrogen peroxide metabolism by controlling the abundance of AOX1A and AXO3/AOX1D in leaf mitochondria (PubMed:25307043). May mediate dephosphorylation of CRT1 and promote the degradation of unfolded proteins in endoplasmic reticulum (ER) (PubMed:22041935). Involved in the regulation of flowering time by repressing FLC, the main flowering repressor gene (PubMed:23976921). 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) (Probable). Interacts with BRI1 (PubMed:26517938). Interacts with IGMT1 and IGMT4 (PubMed:27598402). Interacts with ACO3 in the cytosol (PubMed:25307043). Expressed ubiquitously at low levels (PubMed:9128737). Expressed in roots, emerging lateral roots, cotyledons, leaves, floral stalks and flowers (PubMed:26012558). By heat shock. Wrinkled leaves, stunted growth, delayed flowering and formation of age-dependent yellowing lesions (PubMed:21571669, PubMed:22041935, PubMed:23976921). Conditional phenotype with premature yellowing and constitutive reactive oxygen species (ROS) production in distinct peripheral areas of mature leaves when grown under moderate light intensity and low humidity. May partially evade the accumulation of H(2)O(2) via alternative oxidases (AOX) activity. Increased levels of AOX1A and AOX1D in leaf mitochondria. Increased level of ACO3 phosphorylation. Belongs to the phosphatase 2A regulatory subunit B56 family. The predicted gene At4g15410 has been split into 2 genes: At4g15410 and At4g15415. The predicted gene At4g15410 has been split into 2 genes: At4g15410 and At4g15415.