Characterization of synthetic hydroxyproline-rich proteoglycans with AGP- and extensin-motifs in Arabidopsis as model substrates for hydroxylation and O-glycosylation

ESTEVEZ, JOSE M, KIELISZEWSKI, MARCIA J., NATALIE, KHITROV, SOMERVILLE, CHRIS

Boston

Conferencia; ASPB; 2006

A series of gene constructs encoding synthetic glycomodule peptides with N-terminal signal sequences (ss) and C-terminal green fluorescent proteins (EGFP) were expressed in transgenic Arabidopsis under control of the 35S promoter. The synthetic glycomodule peptides were composed of repetitive proline-containing motifs [(Ser-Pro), (Val-Pro), (Thr-Pro), (Ser-Pro-Pro-Pro), (Ser-Pro-Pro-Pro), etc.] that have been previously found to be substrates for proline hydroxylases and subsequent O-glycosylation of the hydroxyproline residues in Tobacco cells system. In Arabidopsis all of the constructs were secreted in aerial tissues (adult plant) but not in roots at seedling stage. The amount of glycosylation of the various constructs varied depending on the tissue. Some glycomodules were studies in detail and chemical data is presented related with the glycosylation status of the Val-Pro and Ser-Pro repetitive motifs in different tissues of the plant body (i.e leaves and stems). Also, the accumulation of the proteins exhibited a high degree of cell-type specificity within various tissues due to post-transcriptional effects on the proteoglycan biosynthesis. The observations reveal an unexpected level of complexity in the synthesis, secretion, and turnover of the proteoglycans in the plant system. Additionally, expression of several of the constructs led to stunting of root growth and significant changes in the composition of cell wall polysaccharides in leaves and stems. These effects extend previous observations indicating that the glycans of proline-rich glycoproteins have biological activity and open up new opportunities to apply genetic methods to dissecting the underlying mechanisms.