Regulatory subunit of type 2A protein phosphatase. Involved in post-transcriptional regulation of HMGR but not in root growth regulation in response to salt. PP2A consists of a common heterodimeric core enzyme, composed of a 36 kDa catalytic subunit (subunit C) and a 65 kDa constant regulatory subunit (PR65 or subunit A), that associates with a variety of regulatory subunits. Proteins that associate with the core dimer include three families of regulatory subunits B (the R2/B/PR55/B55, R3/B''/PR72/PR130/PR59 and R5/B'/B56 families) and cell signaling molecules. Interacts with HMGR1L and HMGR1S (via N-terminus), but not with HMG2. Interacts with PP2AA1. No visible phenotype. Truncated N-terminus.