Are receptor tyrosine kinases chimeric AGP’s?

Abstract

Arabinogalactan proteins (AGPs) are cell wall proteoglycans with important roles during plant growth and development. They comprise one of the most complex families of macromolecules found in plants, which is in part due to the incredible diversity of the glycans decorating the pro- tein backbone, as well as the heterogeneity of the protein backbones. While this diversity is cer- tainly responsible for the wide array of physiological functions associated with AGPs, it hampers efforts for homology-based identification. We have developed a new method for filtering AGP se- quences that exploits one of their key features, the presence of hydroxyprolines, which represent glycosylation sites. This method was used to filter potential AGPs from Centaurium erythraea RNA- seq data. Most of the filtered sequences had no identifiable domains, while the most frequent identified domains were the Protein kinase and Protein tyrosine kinase domains identified in the same sequences, followed by well-known AGP associates, Leucine rich repeats, Probable lipid transfer, Plastocyanin-like and Fasciclin. It is noteworthy that the Protein (tyrosine) kinase domain has thus far eluded experimental evidence for linkage with AGPs in any plant species, probably due to its transmembrane nature. The implicated sequences were examined in depth and com- pared to homologs from Arabidopsis.