Mutations in a new Arabidopsis cyclophilin disrupt its interaction with protein phosphatase 2A

The heterotrimeric protein phosphatase 2A (PP2A) is a component of multiple signaling pathways in eukaryotes. Disruption of PP2A activity in Arabidops is is known to alter auxin transport and growth response pathways. We demon strated that the regulatory subunit A of an Arabidopsis PP2A interacts with a novel cyclophilin, ROC7. The gene for this cyclophilin encodes a protein that contains a unique 30-amino acid extension at the N-terminus, which di stinguishes the gene product from all previously identified Arabidopsis cyc lophilins, Altered forms of ROC7 cyclophilin with mutations in the conserve d DENFKL domain did not bind to PP2A. Unlike protein phosphatase 2B, PP2A a ctivity in Arabidopsis extracts was not affected by the presence of the cyc lophilin-binding molecule cyclosporin. The ROC7 transcript was expressed to high levels in all tissues tested. Expression of an ROC7 antisense transcr ipt gave rise to increased root growth. These results indicate that cycloph ilin may have a role in regulating PP2A activity, by a mechanism that diffe rs from that employed for cyclophilin regulation of PP2B.