Structural Features of Free N-Glycans Occurring in Developing or Growing Plant Cells and Functional Feature of Plant Endo-β-N-Acetylglucosaminidase

It has been revealed that high-mannose type free N-glycans with one N-acetylglucosamine and plant complex type N-glycans with N-acetylchitobiose segment occur ubiquitously in developing or growing plant cells (hypocotyls of seedlings or developing seeds). Taking account of the reducing-end structure of such free N-glycans, the high-mannose type and plant complex type free glycans would be produced by the action of endo-β-N-acetylglucosaminidase (ENGase) and peptide:N-glycanase (PNGase), respectively. Functional analysis of free N-glycans becomes an interesting subject of plant physiology, since such oligosaccharides have been postulated to have a function as an auxin-like signaling molecule for tomato fruit ripening. In this review, the author provides an overview of the current knowledge of the structural features and putative function of these free N-glycans occurring in plant cells, linking to the functional features of the plant endoglycosidase.