Release, Recycle, Rebuild: Cell-Wall Remodeling, Autodegradation, and Sugar Salvage for New Wall Biosynthesis during Plant Development  William J. Barnes, Charles T. Anderson  Molecular Plant  Volume 11, Issue 1, Pages 31-46 (January 2018) DOI: 10.1016/j.molp.2017.08.011 Copyright © 2017 The Author Terms and Conditions

Figure 1 In Muro Recycling of Primary Cell-Wall Polysaccharide Backbones via Endotransglycosylation. A schematic summary of currently known backbone endotransglycosylase activities detailing glycosyl donor and acceptor oligosaccharides. Exotransglycosylase and endo-trans-α-arabinase activities described in the GHATAbase are not shown (Franková and Fry, 2011). Numbers indicate different types of endotransglycosylation reactions as shown with corresponding polysaccharides in the cell-wall model. The question mark indicates unknown pectin transglycosylase activities. Molecular Plant 2018 11, 31-46DOI: (10.1016/j.molp.2017.08.011) Copyright © 2017 The Author Terms and Conditions

Figure 2 Metabolic Recycling Pathways for Major Primary Cell-Wall Polysaccharides. (A) Schematic of representative xyloglucan, xylan (based on Rennie and Scheller, 2014), homogalacturonan, and cellulose degradation by endogenous plant glycanases, glycosidases, and oxidoreductases resulting in free, apoplastic sugars. Question marks indicate unknown regulation of plant xylanases by XIPs. (B) Sugar uptake into the cytosol is facilitated by SUGAR TRANSPORT PROTEINs (STPs) and potentially unidentified mechanisms. (C) Sugars are metabolically converted by salvage pathways into NDP-sugars that can act as substrates for wall biosynthesis enzymes. FKGP, FUCOKINASE/GDP-FUCOSE PYROPHOSPHORYLASE; HXK, HEXOKINASE; PGM, PHOSPHOGLUCOMUTASE; UDP, UDP-GLUCOSE PYROPHOSPHORYLASE; USP, UDP-SUGAR PYROPHOSPHORYLASE. (D) Reactivated UDP-glucose supports cellulose biosynthesis at the plasma membrane; callose and MLG biosynthesis are not shown. (E) NDP-sugars derived from salvage pathways can be used for the biosynthesis of matrix polysaccharides, which are then delivered to the apoplast. Molecular Plant 2018 11, 31-46DOI: (10.1016/j.molp.2017.08.011) Copyright © 2017 The Author Terms and Conditions