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Proteins undergo posttranslational modifications, such as N-glycosylation, during which a sugar chain is added to the amino acid asparagine at specific sites to form a glycoprotein. N-glycosylation aids cell-to-cell communication as well as pathogen interactions in animals, but scientists know little about this modification in plants.

Syariful Msth via Wikimedia Commons

Oryza sativa in a rice field and surrounding natural scenery in Indonesia.

To address this gap, Cong Lei, Xilong Li and Wenjia Li of Yazhouwan National Laboratory and a research team in China developed a metabolic glycan labeling approach, which they used to map N-glycans in rice. In their Molecular & Cellular Proteomics , the authors grew Oryza sativa, or rice, with a nutrient mixture containing N-azidoacetylgalactosamine, or GalNAz, an artificial glycan building block they could track over time. GalNAz has a unique chemical group to which the authors attached an affinity tag using click chemistry. This made it possible to study the glycoproteins with liquid chromatography–tandem mass spectrometry.

The team identified hundreds of rice-specific N-linked glycoproteins involved in essential biological processes such as plant growth, starch metabolism and protein processing. In addition, several identified proteins mapped to the endoplasmic reticulum–associated protein degradation, or ERAD, pathways, which maintain a balance between protein folding and degradation. The authors also found the core proteins of this pathway to be N-glycosylated in two human cell lines, suggesting that its regulation is conserved between species.

As changes in N-glycosylation have been linked to disrupted plant development, it is important to shed light on modified proteins and sites. This workflow can be used on other plants to expand our understanding of plant glycoproteomes for agricultural research and biotechnology.