Biochemical and Molecular Characterization of AtPAP26, a Vacuolar Purple Acid Phosphatase Up-Regulated in Phosphate-Deprived Arabidopsis Suspension Cells and Seedlings

Abstract

A vacuolar acid phosphatase (APase) that accumulates during phosphate (Pi) starvation of Arabidopsis (Arabidopsis thaliana) suspension cells was purified to homogeneity. The final preparation is a purple APase (PAP), as it exhibited a pink color in solution (A max 5 520 nm). It exists as a 100-kD homodimer composed of 55-kD glycosylated subunits that cross-reacted with an anti-(tomato intracellular PAP)-IgG. BLAST analysis of its 23-amino acid N-terminal sequence revealed that this PAP is encoded by At5g34850 (AtPAP26; one of 29 PAP genes in Arabidopsis) and that a 30-amino acid signal peptide is cleaved from the AtPAP26 preprotein during its translocation into the vacuole. AtPAP26 displays much stronger sequence similarity to orthologs from other plants than to other Arabidopsis PAPs. AtPAP26 exhibited optimal activity at pH 5.6 and broad substrate selectivity. The 5-fold increase in APase activity that occurred in Pi-deprived cells was paralleled by a similar increase in the amount of a 55-kD anti-(tomato PAP or AtPAP26)-IgG immunoreactive polypeptide and a .30-fold reduction in intracellular free Pi concentration. Semiquantitative reverse transcription-PCR indicated that Pi-sufficient, Pi-starved, and Pi-resupplied cells contain similar amounts of AtPAP26 transcripts. Thus, transcriptional controls appear to exert little influence on AtPAP26 levels, relative to translational and/or proteolytic controls. APase activity and AtPAP26 protein levels were also up-regulated in shoots and roots of Pi-deprived Arabidopsis seedlings. We hypothesize that AtPAP26 recycles Pi from intracellular P metabolites in Pi-starved Arabidopsis. As AtPAP26 also exhibited alkaline peroxidase activity, a potential additional role in the metabolism of reactive oxygen species is discussed.

Do plastids inDendrobiumcv. Lucky Duan petals function similar to autophagosomes and autolysosomes?

“…28 In plants intracellular acid phosphatases are mainly located in lytic vacuoles. 29 A cytochemical technique has been used, both in animals and plants, to show total acid phosphatase activity at the ultrastructural level. 25,26 We applied this technique to investigate if plastids in Dendrobium petals show acid phosphatase activity.…”

The Dual-Targeted Purple Acid Phosphatase Isozyme AtPAP26 Is Essential for Efficient Acclimation of Arabidopsis to Nutritional Phosphate Deprivation

“…Pi deprivation induces temporal and tissue-specific expression of PSI APase isozymes (Haran et al, 2000;Wu et al, 2003;Zimmerman et al, 2004;Bozzo et al, 2006) and the concomitant downregulation of other APases (Misson et al, 2005). The transcription factors PHR1, WRKY75, and ZAT6 have been implicated in the control of Arabidopsis PSI APases (Rubio et al, 2001;Devaiah et al, 2007aDevaiah et al, , 2007b, while posttranscriptional mechanisms appear to be essential for the up-regulation of the purple APase (PAP) AtPAP26 during Pi stress (Veljanovski et al, 2006;Tran and Plaxton, 2008;Tran et al, 2010b). In contrast, Pi resupply to 2Pi plants rapidly represses PSI APase genes (del Pozo et al, 1999;Mü ller et al, 2004;Veljanovski et al, 2006) while inducing proteases that target PSI-secreted APases (Bozzo et al, 2004b).…”

“…3.1.3.2) that catalyze the hydrolysis of Pi from various phosphate monoesters and anhydrides in the acidic pH range (Tran et al, 2010a). APase induction by 2Pi plants has been correlated with de novo APase synthesis in several species, including white lupin (Lupinus albus), tomato (Solanum lycopersicum), and Arabidopsis (Arabidopsis thaliana ;Miller et al, 2001;Bozzo et al, 2006;Veljanovski et al, 2006;Bozzo and Plaxton, 2008;Tran and Plaxton, 2008). The probable function of intracellular APases is to recycle Pi from expendable intracel-lular organophosphate pools.…”

“…A variety of intracellular and secreted APases upregulated by 2Pi plants have been characterized as purple APases (PAPs), which represent a specific APase class characterized by a bimetallic active site that endows them with a pink or purple color in solution (del Pozo et al, 1999;Bozzo et al, 2002Bozzo et al, , 2004aBozzo et al, , 2006Veljanovski et al, 2006;Tran et al, 2010b). Although mammals contain a pair of PAP-encoding genes, vascular plant PAPs belong to a large multigene family.…”

“…The transcription factors PHR1, WRKY75, and ZAT6 have been implicated in the control of Arabidopsis PSI APases (Rubio et al, 2001;Devaiah et al, 2007aDevaiah et al, , 2007b, while posttranscriptional mechanisms appear to be essential for the up-regulation of the purple APase (PAP) AtPAP26 during Pi stress (Veljanovski et al, 2006;Tran and Plaxton, 2008;Tran et al, 2010b). In contrast, Pi resupply to 2Pi plants rapidly represses PSI APase genes (del Pozo et al, 1999;Mü ller et al, 2004;Veljanovski et al, 2006) while inducing proteases that target PSI-secreted APases (Bozzo et al, 2004b). Further characterization of PSI APases is required to define the molecular mechanisms underlying this archetypical plant response to Pi starvation, as well as to identify additional targets for biotechnological improvement of crop Pi acquisition.…”