Abstract
The protein phosphatase PP2A is essential for the control of integrated eukaryotic cell functioning. Several cellular and developmental events, e.g., plant growth regulator (PGR) mediated signaling pathways are regulated by reversible phosphorylation of vesicle traffic proteins. Reviewing present knowledge on the relevant role of PP2A is timely. We discuss three aspects: (1) PP2A regulates microtubule-mediated vesicle delivery during cell plate assembly. PP2A dephosphorylates members of the microtubule associated protein family MAP65, promoting their binding to microtubules. Regulation of phosphatase activity leads to changes in microtubule organization, which affects vesicle traffic towards cell plate and vesicle fusion to build the new cell wall between dividing cells. (2) PP2A-mediated inhibition of target of rapamycin complex (TORC) dependent signaling pathways contributes to autophagy and this has possible connections to the brassinosteroid signaling pathway. (3) Transcytosis of vesicles transporting PIN auxin efflux carriers. PP2A regulates vesicle localization and recycling of PINs related to GNOM (a GTP–GDP exchange factor) mediated pathways. The proper intracellular traffic of PINs is essential for auxin distribution in the plant body, thus in whole plant development. Overall, PP2A has essential roles in membrane interactions of plant cell and it is crucial for plant development and stress responses.
Highlights
Protein kinases and phosphatases are working as “Yin and Yang” in the phosphoregulation of proteins since their phosphorylation is mostly reversible [1]
Since all members of the microtubule associated proteins (MAPs)-65 family are controlled by PP2A, we can predict that the phosphatase is not functional at this stage and site, MAP65-3 remains phosphorylated and subsequently releases MTs at the lagging zone of phragmoplast
At the basal pole of the cell, PIN1 is phosphorylated by brefeldin A (BFA) sensitive D6 protein kinase (D6PK) to drive auxin efflux and its local recycling and PP2A dephosphorylates it to drive its transcytosis into the apical cell pole
Summary
Protein kinases and phosphatases are working as “Yin and Yang” in the phosphoregulation of proteins since their phosphorylation is mostly reversible [1]. The complete phragmoplast appears in parallel with the disassembly of mitotic spindle and is characteristic for telophase and cytokinesis It contains microfilaments, antiparallel arrays of MT bundles, Golgi-derived vesicles bound to MTs and a wide set of macromolecules including microtubule associated proteins (MAPs) that regulate assembly and functioning of this peculiar structure. Since all members of the MAP-65 family are controlled by PP2A, we can predict that the phosphatase is not functional at this stage and site, MAP65-3 remains phosphorylated and subsequently releases MTs at the lagging zone of phragmoplast (see more explanations at Figure 1). This hypothesis should be confirmed by further experiments
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