A maize homologue of the bacterial CMP-3-deoxy-D-manno-2-octulosonate (KDO) synthetases -: Similar pathways operate in plants and bacteria for the activation of KDO prior to its incorporation into outer cellular envelopes

The eight-carbon acid sugar 3-deoxy-D-manno-2-octulosonate (KDO) is an essential component of Gram-negative bacterial cell walls and capsular polysaccharides. KDO is incorporated into these polymers as CMP-KDO, which is produced in an unusual activation step catalyzed by the enzyme CMP-KDO synthetase. CMP-KDO synthetase activity has traditionally been considered exclusive to Gram-negative bacteria. CMP-KDO synthetase inhibitors attract great interest owing to their potential as selective bactericides. The sugar KDO is also a component of the rhamnogalacturonan II pectin fraction of the primary cell walls of most higher plants and of the cell wall polysaccharides of some green algae. However, the metabolic pathway leading to its incorporation into the plant cell mall is unknown. This paper describes the isolation and characterization of a maize gene, which codes for a protein very similar in sequence and activity to prokaryotic CMP-KDO synthetases. Remarkably, the maize gene can complement a CMP-KDO synthetase (kdsB) Salmonella typhimurium mutant defective in cell wall synthesis, ZmCKS activity is novel in eukaryotes, The evolutionary origin of ZmCKS is discussed in relation to the high degree of conservation between the plant and bacterial genes and its atypical codon usage in maize.