title: The cell wall-targeted purple acid phosphatase AtPAP25 is critical for acclimation of Arabidopsis thaliana to nutritional phosphorus deprivation.
abstract: Plant purple acid phosphatases (PAPs) belong to a relatively large gene family whose individual functions are poorly understood. Three PAP isozymes that are up-regulated in the cell walls of phosphate (Pi)-starved (-Pi) Arabidopsis thaliana suspension cells were purified and identified by MS as AtPAP12 (At2g27190), AtPAP25 (At4g36350) and AtPAP26 (At5g34850). AtPAP12 and AtPAP26 were previously isolated from the culture medium of -Pi cell cultures, and shown to be secreted by roots of Arabidopsis seedlings to facilitate Pi scavenging from soil-localized organophosphates. AtPAP25 exists as a 55 kDa monomer containing complex NX(S/T) glycosylation motifs at Asn172, Asn367 and Asn424. Transcript profiling and immunoblotting with anti-AtPAP25 immune serum indicated that AtPAP25 is exclusively synthesized under -Pi conditions. Coupled with potent mixed-type inhibition of AtPAP25 by Pi (I50 = 50 μm), this indicates a tight feedback control by Pi that prevents AtPAP25 from being synthesized or functioning as a phosphatase except when Pi levels are quite low. Promoter-GUS reporter assays revealed AtPAP25 expression in shoot vascular tissue of -Pi plants. Development of an atpap25 T-DNA insertion mutant was arrested during cultivation on soil lacking soluble Pi, but rescued upon Pi fertilization or complementation with AtPAP25. Transcript profiling by quantitative RT-PCR indicated that Pi starvation signaling was attenuated in the atpap25 mutant. AtPAP25 exhibited near-optimal phosphatase activity with several phosphoproteins and phosphoamino acids as substrates. We hypothesize that AtPAP25 plays a key signaling role during Pi deprivation by functioning as a phosphoprotein phosphatase rather than as a non-specific scavenger of Pi from extracellular P-monoesters.
authors.affiliation: Department of Biology, Queen's University, Kingston, ON, K7L 3N6, Canada.
authors.forename: Hernan A
authors.initials: HA
authors.lastname: Del Vecchio
authors.forename: Sheng
authors.initials: S
authors.lastname: Ying
authors.forename: Joonho
authors.initials: J
authors.lastname: Park
authors.forename: Vicki L
authors.initials: VL
authors.lastname: Knowles
authors.forename: Satomi
authors.initials: S
authors.lastname: Kanno
authors.forename: Keitaro
authors.initials: K
authors.lastname: Tanoi
authors.forename: Yi-Min
authors.initials: YM
authors.lastname: She
authors.forename: William C
authors.initials: WC
authors.lastname: Plaxton
mesh_terms: D000064:Acclimatization; D000135:Acid Phosphatase / Q000235:genetics / Q000378:metabolism*; D000222:Adaptation, Physiological; D017360:Arabidopsis / Q000166:cytology / Q000235:genetics / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002473:Cell Wall / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D006023:Glycoproteins / Q000378:metabolism; D006031:Glycosylation; D009154:Mutation; D010758:Phosphorus / Q000378:metabolism*; D018517:Plant Roots / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D011401:Promoter Regions, Genetic
chemical_list: D029681:Arabidopsis Proteins; D006023:Glycoproteins; D010758:Phosphorus; C091137:purple acid phosphatase; D000135:Acid Phosphatase; C000607126:PAP25 protein, Arabidopsis
keywords: Arabidopsis thaliana (thale cress); cell-wall proteome; functional genomics; phosphorus nutrition; purple acid phosphatase