TARGETED MUTAGENESIS OF ACYL-LIPID DESATURASES IN SYNECHOCYSTIS - EVIDENCE FOR THE IMPORTANT ROLES OF POLYUNSATURATED MEMBRANE-LIPIDS IN GROWTH, RESPIRATION AND PHOTOSYNTHESIS

Acyl-lipid desaturases introduce double bonds (unsaturated bonds) at s pecifically defined positions in fatty acids that are esterified to th e glycerol backbone of membrane glycerolipids. The desA, desB and desD genes of Synechocystis sp. PCC 6803 encode acyl-lipid desaturases tha t introduce double bonds at the Delta 12, omega 3 and Delta 6 position s of C-18 fatty acids respectively. The mutation of each of these gene s by insertion of an antibiotic resistance gene cartridge completely e liminated the corresponding desaturation reaction. This system allowed us to manipulate the number of unsaturated bonds in membrane glycerol ipids in this organism in a step-wise manner. Comparisons of the vario usly mutated cells revealed that the replacement of all polyunsaturate d fatty acids by a monounsaturated fatty acid suppressed growth of the cells at low temperature and, moreover, it decreased the tolerance of the cells to photoinhibition of photosynthesis at low temperature by suppressing recovery of the photosystem II protein complex from photoi nhibitory damage, However, the replacement of tri- and tetraunsaturate d fatty acids by a diunsaturated fatty acid did not have such effects, These findings indicate that polyunsaturated fatty acids are importan t in protecting the photosynthetic machinery from photoinhibition at l ow temperatures.