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Plant J. 2017 Aug;91(4):613-630. doi: 10.1111/tpj.13591. Epub 2017 Jun 13.

Arabidopsis thaliana FLA4 functions as a glycan-stabilized soluble factor via its carboxy-proximal Fasciclin 1 domain.

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Department of Applied Genetics and Cell Biology, University of Natural Resources and Life Science, BOKU Vienna, Muthgasse 11, A-1190, Vienna, Austria.
Department of Biochemistry, University of Cambridge, Cambridge, CB2 1QW, UK.
Department of Chemistry, University of Natural Resources and Life Science, BOKU Vienna, Muthgasse 11, A-1190, Vienna, Austria.
Biología Molecular y Neurociencias-Consejo Nacional de Investigaciones Científicas y Técnicas(IFIByNE-CONICET), Instituto de Fisiología, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, C1428EGA, Argentina.
Fundación Instituto Leloir and Instituto de Investigaciones Bioquímicas de Buenos Aires, Buenos Aires CP, C1405BWE, Argentina.


Fasciclin-like arabinogalactan proteins (FLAs) are involved in numerous important functions in plants but the relevance of their complex structure to physiological function and cellular fate is unresolved. Using a fully functional fluorescent version of Arabidopsis thaliana FLA4 we show that this protein is localized at the plasma membrane as well as in endosomes and soluble in the apoplast. FLA4 is likely to be GPI-anchored, is highly N-glycosylated and carries two O-glycan epitopes previously associated with arabinogalactan proteins. The activity of FLA4 was resistant against deletion of the amino-proximal fasciclin 1 domain and was unaffected by removal of the GPI-modification signal, a highly conserved N-glycan or the deletion of predicted O-glycosylation sites. Nonetheless these structural changes dramatically decreased endoplasmic reticulum (ER)-exit and plasma membrane localization of FLA4, with N-glycosylation acting at the level of ER-exit and O-glycosylation influencing post-secretory fate. We show that FLA4 acts predominantly by molecular interactions involving its carboxy-proximal fasciclin 1 domain and that its amino-proximal fasciclin 1 domain is required for stabilization of plasma membrane localization. FLA4 functions as a soluble glycoprotein via its carboxy-proximal Fas1 domain and its normal cellular trafficking depends on N- and O-glycosylation.


Arabidopsis thaliana ; GPI-anchor; N-glycan; O-glycan; arabinogalactan protein; fasciclin

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