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

Abstract

Itis not yet known whether dephosphorylation of proteins catalyzed by phosphatases occurs in the apoplastic space. In this study, we found that tobacco (Nicotiana tabacum) purple acid phosphatase could dephosphorylate the phosphoryl residues of three apoplastic proteins, two of which were identified as a-xylosidase and b-glucosidase. The dephosphorylation and phosphorylation of recombinant a-xylosidase resulted in a decrease and an increase in its activity, respectively, when xyloglucan heptasaccharide was used as a substrate. Attempted overexpression of the tobacco purple acid phosphatase NtPAP12 in tobacco cells not only decreased the activity levels of the glycosidases but also increased levels of xyloglucan oligosaccharides and cello-oligosaccharides in the apoplast during the exponential phase. We suggest that purple acid phosphatase controls the activity of a-xylosidase and b-glucosidase, which are responsible for the degradation of xyloglucan oligosaccharides and cello-oligosaccharides in the cell walls.

Xyloglucan Metabolism Differentially Impacts the Cell Wall Characteristics of the Endosperm and Embryo during Arabidopsis Seed Germination

“…Moreover, a pI shift has also been observed due to protein phosphorylation. Such phosphorylation would lead to activation of the protein (Kaida et al, 2010), whereas the glycosylation that takes place in the Golgi apparatus would mediate activity modifications and induce protein secretion to cell walls (Ruiz-May et al, 2012). It is likely, therefore, that the mass and pI shifts detected in dry seed extracts correspond to XYL1 polypeptides targeted to the wall after glycosylation processes in the Golgi as well as differentially phosphorylated isoforms.…”

Lack of α-Xylosidase Activity in Arabidopsis Alters Xyloglucan Composition and Results in Growth Defects

“…Some of this heterogeneity can be explained by differences in glycosylation or by an N-terminal propeptide that seems to be lost within the wall (Sampedro et al, 2001;Albenne et al, 2009). More surprising is the fact that some forms of AtXYL1 appear to be phosphorylated and that dephosphorylation by cell wall phosphatases could lead to inactivation (Kwon et al, 2005;Kaida et al, 2010).…”

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.…”

“…In addition, the counterparts of the AtPAP10 gene have been found in a wide range of plant species (Supplemental Fig. S3), including rice (Oryza sativa; Zhang et al, 2011) and tobacco (Kaida et al, 2010). These genes may also represent useful targets for engineering crops with high P nutrition.…”