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 esse ntial component of Gram-negative bacterial cell walls and capsular polysacc harides. KDO is incorporated into these polymers as CMP-KDO, which is produ ced in an unusual activation step catalyzed by the enzyme CMP-KDO synthetas e. CMP-KDO synthetase activity has traditionally been considered exclusive to Gram-negative bacteria. CMP-KDO synthetase inhibitors attract great inte rest owing to their potential as selective bactericides. The sugar KDO is a lso a component of the rhamnogalacturonan II pectin fraction of the primary cell walls of most higher plants and of the cell wall polysaccharides of s ome green algae. However, the metabolic pathway leading to its incorporatio n into the plant cell mall is unknown. This paper describes the isolation a nd characterization of a maize gene, which codes for a protein very similar in sequence and activity to prokaryotic CMP-KDO synthetases. Remarkably, t he maize gene can complement a CMP-KDO synthetase (kdsB) Salmonella typhimu rium mutant defective in cell wall synthesis, ZmCKS activity is novel in eu karyotes, The evolutionary origin of ZmCKS is discussed in relation to the high degree of conservation between the plant and bacterial genes and its a typical codon usage in maize.