Expanding the Scope of Metabolic Glycan Labeling in Arabidopsis thaliana.

Metabolic glycan labeling (MGL) has gained wide utility and has become a useful tool for probing glycosylation in living systems. For the past three decades, the development and application of MGL have mostly focused on animal glycosylation. Recently, exploiting MGL for studying plant glycosylation has gained interest. Here, we describe a systematic evaluation of MGL for fluorescence imaging of root glycans in Arabidopsis thaliana. Nineteen monosaccharide analogues containing a bioorthogonal group (azide, alkyne, or cyclopropene) were synthesized and evaluated for metabolic incorporation into root glycans. Among these unnatural sugars, 14 (including three new compounds) were evaluated in plants for the first time. Our results showed that five unnatural sugars metabolically labeled root glycans efficiently, and enabled fluorescence imaging by bioorthogonal conjugation with fluorophores. We optimized the experimental procedures for MGL in Arabidopsis. Finally, distinct distribution patterns of the newly synthesized glycans were observed along the root developmental zones, thus indicating regulated biosynthesis of glycans during root development. We envision that MGL will find broad applications in plant glycobiology.