Activation of β-Glucan Synthases by Wall-Bound Purple Acid Phosphatase in Tobacco Cells    

Abstract

Wall-bound purple acid phosphatases have been shown to be potentially involved in the regulation of plant cell growth. The aim of this work was to further investigate the function of one of these phosphatases in tobacco (Nicotiana tabacum), NtPAP12, using transgenic cells overexpressing the enzyme. The transgenic cells exhibited a higher level of phosphatase activity in their walls. The corresponding protoplasts regenerating a cell wall exhibited a higher rate of b-glucan synthesis and cellulose deposition was increased in the walls of the transgenic cells. A higher level of plasma membrane glucan synthase activities was also measured in detergent extracts of membrane fractions from the transgenic line, while no activation of Golgi-bound glycan synthases was detected. Enzymatic hydrolysis and methylation analysis were performed on the products synthesized in vitro by the plasma membrane enzymes from the wild-type and transgenic lines extracted with digitonin and incubated with radioactive UDP-glucose. The data showed that the glucans consisted of callose and cellulose and that the amount of each glucan synthesized by the enzyme preparation from the transgenic cells was significantly higher than in the case of the wildtype cells. The demonstration that callose and cellulose synthases are activated in cells overexpressing the wall-bound phosphatase NtPAP12 suggests a regulation of these carbohydrate synthases by a phosphorylation/dephosphorylation process, as well as a role of wall-bound phosphatases in the regulation of cell wall biosynthesis.

Potential Role for Purple Acid Phosphatase in the Dephosphorylation of Wall Proteins in Tobacco Cells

“…Transgenic cells overexpressing NtPAP12 under the control of a constitutive promoter were generated (Kaida et al, 2009). The activity of the phosphatase was greater in the walls of the transgenic cells than in the wild-type cells by a factor of 20 (Table II).…”

“…Only a few functions have been suggested for these phosphatases: AtPAP15 seems to modulate ascorbic acid biosynthesis (Zhang et al, 2008), and AtPAP17 may play a role in the metabolism of reactive oxygen species (del Pozo et al, 1999). In other plant species, soybean (Glycine max) GmPAP3 is induced by NaCl stress but not by phosphorus deficiency (Liao et al, 2003), tomato (Solanum lycopersicum) PAP may release phosphate from extracellular phosphate ester under phosphate starvation (Bozzo et al, 2002), and tobacco (Nicotiana tabacum) NtPAP12 could be involved in the deposition of b-glucan (Kaida et al, , 2009Sano et al, 2003). Mammalian PAPs, which are secretory enzymes, may be involved in iron transport (Nuttleman and Roberts, 1990), generation of reactive oxygen species (Sibille et al, 1987), and bone resorption (EkRylander et al, 1994).…”

“…We previously demonstrated that the activities of cellulose and callose synthases are enhanced by overexpression of NtPAP12 in tobacco cells (Kaida et al, 2009). The phosphorylation/dephosphorylation process in those synthases may occur directly on the catalytic subunit itself, which has been predicted to be located on the cytoplasmic side of the plasma membrane (Nü hse et al, 2004;Taylor, 2007).…”

The Arabidopsis Purple Acid Phosphatase AtPAP10 Is Predominantly Associated with the Root Surface and Plays an Important Role in Plant Tolerance to Phosphate Limitation

“…NtPAP12 is a cell wallbound PAP in tobacco with a protein sequence very similar to that of AtPAP10. Studies have shown that NtPAP12 could dephosphorylate and activate some cell wall-bound enzymes, such as a-xylosidase and b-glucosidase, which are involved in the biosynthesis of cell walls (Kaida et al, 2009(Kaida et al, , 2010. It is possible, therefore, that AtPAP10, like NtPAP12, may function in regulating the growth of root cells through the control of cell wall biosynthesis when plants are stressed by Pi deficiency.…”

A Peroxidase-Dependent Apoplastic Oxidative Burst in Cultured Arabidopsis Cells Functions in MAMP-Elicited Defense

“…S6, band 29). PAPs are involved in the induction of b-glucan synthases in the cell wall (Kaida et al, 2009(Kaida et al, , 2010. PGIPs, which, as discussed above, are also upregulated in IG-2 and IG-3, play an important role in cell growth in addition to pathogen defense.…”