Expression Levels Of Genes In Carotenoids Biosynthetic Pathway And Metabolism Profiling Of Dunaliella Salina Under Nutrient Deprivations

Dunaliella salina(D.salina)is a cell wall-less green microalgae that can overproduce carolenoids under the adverse conditions of high irradiance,high salinity,or low nutritions.This paper studied the influence of nutrition deprivations to growth,accumulation of carotenoids,activity of antioxidant enzymes,expression level of key genes in carotenoids biosynthetic pathway and molecule metabolites of D.salina,it provided a new strategy and theoretical basis for D.salina overproducing carotenoids.Under different nutrient deprivations conditions,nitrogen-deprivation(-N)was the most effective for growth,followed phosphorus-deprivation(-P)?and sulfur-deprivation(-S)only affected the early stage of growth significantly,then the effect weakened later.When lacking of several kind of nutrients,the cumulative effects on physiological and biochemical characteristics of D.salina were dramatical,especially the accumulation of carotenoids and ?-carotene appeared more evident under nitrogen/phosphorus co-deprivation(-N-P)and nitrogen/sulfur co-deprivation(-N-S).Under nutrient deprivations,D.salina look advantage of intracellular nutrients stored for growth;when cells lacked of nutrition,its growth would slow down or even stop,and synthetic some special material to protect the cells.Through studying the expression levels of genes in carotenoids biosynthetic pathway by Real-Time PCR,the results showed that the expression levels were downregulated under-N-P,-N-S and nitrogen/phosphorus/sulfur co-deprivation(-N-P-S),but the accumulation of carotenoids and ?-carotene were increased during nutrient co-deprivations and higher than that under single kind of nutrient deprivation conditions.Futhermore,the study showed that nutrient deprivations caused the changes of metabolites involved in carbohydrates.lipids and amino acid;and metabolites detected under different nutrient deprivations were similar;in addition,the major labeled metabolites are fatty acids,amino acids and sugars,such as palmitic acid,proline and sucrose and so on.Urea cycle were inhibited under sulfur-deprivation severely,while TCA cycle,urea cycle and synthesis of amino acids all were inhibited under-N-P-S condition.However,with nutrient deprivations,protective substances,such as proline,glutamic acid and some monosaccharides,as well as sucrose,fatty acids,increased.The content of 2-oxoglutarate also increased,this indicated there was a clear trend to synthetic carotenoids.In conclusion,different nutrient deprivations would cause different changes in physiological and biochemical characteristics of D.salina.When lacking of several kind of nutrients,accumulation of carotenoids and ?-carotene would show cumulative effect significantly,but the expression levels of the genes corresponding did not exhibit the same cumulative effect,The results showed that an increase in accumulation of carotenoids were the outcome of the transcription and translation.F rom the changes of major metabolites,the influences of sulfur element were stronger than the other two elements,and the cells were more biased in favor of synthesis of carbohydrates,such as sucrose,maltose,organic acids,etc.,and turned to synthesis of carotenoids,and protective substances of cells increased.