Arabidopsis thaliana FLA4 functions as a glycan‐stabilized soluble factor via its carboxy‐proximal Fasciclin 1 domain. (13th June 2017)

• Record Type: Journal Article
• Authors: Xue, Hui; Veit, Christiane; Abas, Lindy; Tryfona, Theodora; Maresch, Daniel; Ricardi, Martiniano M.; Estevez, José Manuel; Strasser, Richard; Seifert, Georg J.
• Is Part Of: Plant journal. Volume 91:Number 4(2017)
• Page Start: 613
• Page End: 630
• Publication Date: 2017-06-13
• Subjects: arabinogalactan protein -- fasciclin -- GPI‐anchor -- N‐glycan -- O‐glycan -- Arabidopsis thaliana; Plant molecular biology -- Periodicals; Plant cells and tissues -- Periodicals; Botany -- Periodicals; 580
• DOI: 10.1111/tpj.13591
• Languages: English
• ISSNs: 0960-7412

Abstract

Summary: 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. Significance Statement: FLA4, a protein involved in root growth, salt tolerance and seed coat mucilage development consists of two fasciclin domains, multiple predicted glycosylation sites and a GPI‐anchoring motif. The functional significance of these features is elusive. Our structural functional dissection shows that the carboxy terminal fasciclin domain is crucial for FLA4 function while the amino‐terminal fasciclin domain, GPI‐anchoring N‐ linked and O‐ linked glycosylation are important for intracellular trafficking but not for function.