An Arabidopsis cell wall proteoglycan consists of pectin and arabinoxylan covalently linked to an arabinogalactan protein.
Plant cell walls are comprised largely of the polysaccharides cellulose, hemicellulose, and pectin, along with ∼10% protein and up to 40% lignin. These wall polymers interact covalently and noncovalently to form the functional cell wall. Characterized cross-links in the wall include covalent linkages between wall glycoprotein extensins between rhamnogalacturonan II monomer domains and between polysaccharides and lignin phenolic residues. Here, we show that two isoforms of a purified Arabidopsis thaliana arabinogalactan protein (AGP) encoded by hydroxyproline-rich glycoprotein family protein gene At3g45230 are covalently attached to wall matrix hemicellulosic and pectic polysaccharides, with rhamnogalacturonan I (RG I)/homogalacturonan linked to the rhamnosyl residue in the arabinogalactan (AG) of the AGP and with arabinoxylan attached to either a rhamnosyl residue in the RG I domain or directly to an arabinosyl residue in the AG glycan domain. The existence of this wall structure, named ARABINOXYLAN PECTIN ARABINOGALACTAN PROTEIN1 (APAP1), is contrary to prevailing cell wall models that depict separate protein, pectin, and hemicellulose polysaccharide networks. The modified sugar composition and increased extractability of pectin and xylan immunoreactive epitopes in apap1 mutant aerial biomass support a role for the APAP1 proteoglycan in plant wall architecture and function.
Complex Carbohydrate Research Center, University of Georgia, Athens, Georgia 30602-4712, USA.
Li
L
Tan
Stefan
S
Eberhard
Sivakumar
S
Pattathil
Clayton
C
Warder
John
J
Glushka
Chunhua
C
Yuan
Zhangying
Z
Hao
Xiang
X
Zhu
Utku
U
Avci
Jeffrey S
JS
Miller
David
D
Baldwin
Charles
C
Pham
Ronald
R
Orlando
Alan
A
Darvill
Michael G
MG
Hahn
Marcia J
MJ
Kieliszewski
Debra
D
Mohnen
D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal / Q000276:immunology; D017360:Arabidopsis / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D018533:Biomass; D002473:Cell Wall / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D000939:Epitopes; D006023:Glycoproteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D008961:Models, Structural; D008969:Molecular Sequence Data; D009088:Mucoproteins / Q000737:chemistry* / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D009154:Mutation; D010368:Pectins / Q000737:chemistry* / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D011134:Polysaccharides / Q000737:chemistry / Q000378:metabolism; D020033:Protein Isoforms; D011509:Proteoglycans / Q000737:chemistry* / Q000378:metabolism; D040901:Proteomics; D014990:Xylans / Q000737:chemistry* / Q000378:metabolism
D000911:Antibodies, Monoclonal; D029681:Arabidopsis Proteins; C583977:At3g45230 protein, Arabidopsis; D000939:Epitopes; D006023:Glycoproteins; D009088:Mucoproteins; D010940:Plant Proteins; D011134:Polysaccharides; D020033:Protein Isoforms; D011509:Proteoglycans; D014990:Xylans; C006619:arabinogalactan proteins; C042491:rhamnogalacturonan I; C042492:rhamnogalacturonan II; C007916:hemicellulose; D010368:Pectins; C085118:arabinoxylan