b'Plant ScienceContinued42 The Long Reach ofSugar-Tagged ProteinsPhotosynthesis converts carbon dioxide into sugar, the source of energy for all life. The amount of sugar . . .until now itsavailable in the body or cell must be monitored to role in plantshascontrol normal metabolism and growth in animals and plants. One of these control mechanisms is remained elusive. . . to modify proteins with sugar molecules, such as O-linked acetylglucosamine (O-GlcNAc). Protein O-GlcNAc modification is very important to a rangeCarnegie researchers Shouling Xu, Dasha Savage, of cellular, physiological, and disease processes inand Zhiyong Wang with colleagues have for the mammals. Altered levels of this modification havefirst time identified 262 proteins and their sites been associated with diabetes, cardiovascularthat are modified by O-GlcNAc in a plant. Many disease, and cancer. However, until now its role inof these proteins are known to regulate important plants has remained elusive.processes, such as gene activation, response to hormones, and the timing of flowering. This work lays the foundation for further understanding of the importance of O-GlcNAc modification to plant growth and crop productivity.Genetic evidence shows that when two enzymes, SPINDLY and SECRET AGENT, that carry out this modification are inactivated, the plant embryo dies. But very few proteins modified by O-GlcNAc had OH been identified in plants. HO O The team conducted a large-scale proteomic analysis HO OAcNH of the model plant Arabidopsis thaliana. (Proteomics is the large-scale study of proteins.) They extracted Protein proteins from inflorescence tissue, broke the proteins into constituent peptides, and then enriched O-GlcNAc-modified peptides using a technique The team studies O-GlcNAc modifications in the modelcalled lectin weak affinity chromatography. They plant Arabidopsis (background). The inset shows how a sugarthen employed mass spectrometry to determine molecule is attached to the protein when it undergoes thethe sequence of the peptides and the amino acid O-GlcNAcylation modification process. Image courtesy Shouling Xu'