Recent Advances on the Posttranslational Modifications of EXTs and Their Roles in Plant Cell Walls

The genetic set up and the enzymes that define the O-glycosylation sites and transfer the activated sugars to cell wall glycoprotein Extensins (EXTs) have remained unknown for a long time. We are now beginning to see the emerging components of the molecular machinery that assembles these complex O-glycoproteins on the plant cell wall. Genes conferring the posttranslational modifications, i.e., proline hydroxylation and subsequent O-glycosylation, of the EXTs have been recently identified. In this review we summarize the enzymes that define the O-glycosylation sites on the O-glycoproteins, i.e., the prolyl 4-hydroxylases (P4Hs), the glycosyltransferases that transfer arabinose units (named arabinosyltransferases, AraTs), and the one responsible for transferring a single galactose (galactosyltransferase, GalT) on the protein EXT backbones. We discuss the effects of posttranslational modifications on the structure and function of extensins in plant cell walls

Exocyst mutants suppress pollen tube growth and cell wall structural defects of hydroxyproline O‐arabinosyltransferase mutants

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/156472/1/tpj14808-sup-0003-FigS3.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156472/9/tpj14808.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156472/8/tpj14808-sup-0001-FigS1.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156472/7/tpj14808-sup-0004-FigS4.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156472/6/tpj14808-sup-0005-FigS5.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156472/5/tpj14808-sup-0007-FigS7.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156472/4/tpj14808-sup-0006-FigS6.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156472/3/tpj14808-sup-0002-FigS2.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156472/2/tpj14808_am.pd

Different genetic strategies to generate high amylose starch mutants by engineering the starch biosynthetic pathways

This review systematically documents the major different strategies of generating high-amylose (HAS) starch mutants aiming at providing high resistant starch, by engineering the starch biosynthesis metabolic pathways. We identify three main strategies based on a new representation of the starch structure: 'the building block backbone model': i) suppression of starch synthases for reduction of amylopectin (AP) side-chains; ii) suppression of starch branching enzymes (SBEs) for production of AM-like materials; and iii) suppression of debranching enzymes to restrain the transformation from over-branched pre-AP to more ordered AP. From a biosynthetic perspective, AM generated through the second strategy can be classified into two types: i) normal AM synthesized mainly by regular expression of granule-bound starch synthases, and ii) modified linear AP chains (AM-like material) synthesized by starch synthases due to the suppression of starch branching enzymes. The application of new breeding technologies, especially CRISPR, in the breeding of HAS crops is also reviewed

Identification and evolution of a plant cell wall specific glycoprotein glycosyl transferase, ExAD

Extensins are plant cell wall glycoproteins that act as scaffolds for the deposition of the main wall carbohydrate polymers, which are interlocked into the supramolecular wall structure through intra- and inter-molecular iso-di-tyrosine crosslinks within the extensin backbone. In the conserved canonical extensin repeat, Ser-Hyp(4), serine and the consecutive C4-hydroxyprolines (Hyps) are substituted with an α-galactose and 1–5 β- or α-linked arabinofuranoses (Arafs), respectively. These modifications are required for correct extended structure and function of the extensin network. Here, we identified a single Arabidopsis thaliana gene, At3g57630, in clade E of the inverting Glycosyltransferase family GT47 as a candidate for the transfer of Araf to Hyp-arabinofuranotriose (Hyp-β1,4Araf-β1,2Araf-β1,2Araf) side chains in an α-linkage, to yield Hyp-Araf(4) which is exclusively found in extensins. T-DNA knock-out mutants of At3g57630 showed a truncated root hair phenotype, as seen for mutants of all hitherto characterized extensin glycosylation enzymes; both root hair and glycan phenotypes were restored upon reintroduction of At3g57630. At3g57630 was named Extensin Arabinose Deficient transferase, ExAD, accordingly. The occurrence of ExAD orthologs within the Viridiplantae along with its’ product, Hyp-Araf(4), point to ExAD being an evolutionary hallmark of terrestrial plants and charophyte green algae