LIGHT-INDUCED EXPRESSION OF FATTY-ACID DESATURASE GENES

In cyanobacterial cells, fatty acid desaturation is one of the crucial steps in the acclimation processes to low-temperature conditions, The expression of all the four acyl lipid desaturase genes of Synechocyst is PCC 6803 was studied as a function of temperature and separately as a function of light. We used cells grown at 25 degrees C in light-act ivated hetero trophic growth conditions. In these cells, the productio n of alpha-linolenic acid and 18:4 fatty acids was negligible and the synthesis of gamma-linolenic acid was remarkably suppressed compared w ith those of the cells grown photoautotrophically. The cells grown in the light in the presence of glucose show ed no difference in fatty ac id composition compared with cells grown photoautotrophically. The lev el of desC mRNA for Delta 9 desaturase was not affected by either the temperature or the light. It was constitutively expressed at 25 degree s C with and without illumination. The level of desB transcripts was n egligible in the dark-grown cells and was enhanced about 10-fold by ex posure of the cells to light. The maximum level of expression occurred within 15 min. The level of desA and desD mRNAs was higher in dark-gr own cells than that of desB mRNA for omega 3 desaturase. However, the induction of both desA and desD mRNAs for Delta 12 and Delta 6 desatur ases, respectively, was enhanced by light about 10-fold, Rifampicin, c hloramphenicol, and 3-(3,4-dichlorophenyl)-1,1-dimethylurea completely blocked the induction of the expression of desA, desB, and desD, Cons equently, we suggest the regulatory role of light via photosynthetic p rocesses in the induction of the expression of acyl lipid desaturases.