The KEGG LIGAND database contains information about chemical structures and chemical reactions of endogenous molecules, small molecules to larger biopolymers. Certain KEGG pathway maps contain reference chemical structures that can be used to link genomes to the chemical diversity of endogenous molecules. For example, the KEGG pathway map for N-glycan biosynthesis (map00510) contains both the biosynthetic pathway and the synthesized glycan structure. By mapping the genomic content of glycosyltransferases, such as for human (hsa00510), the organism-specific pathway and the organism-specific glycan structure can be seen. This type of structural mapping has been done more extensively in eukaryotic genomes to characterize the chemical structural diversity of glycans (11) and lipids (12). A potentially more interesting, but more difficult, problem is to link plant genomes to plant secondary metabolites. Plants are known to produce diverse chemical compounds including those with medicinal and nutritional values, but the chemical architecture is more complex than simple biopolymers of glycans and lipids. We have introduced KEGG PLANT, a new interface to the KEGG resource for plant research, especially for understanding relationships between genomic and chemical information of plant natural products.
