The Response Mechanism Of Carotenoid Biosynthesis Pathway Under Different Intensities And Wavelengths Of Light In Dunaliella Salina

Dunaliella salina was isolated,purified,sequenced,and identified from samples with high salinity in Hangu,Tianjin,China.Algal growth,transcriptome,and acclimation mechanisms in D.salina were investigated in response to different intensities and wavelengths of light.The photosynthesis inhibitors were added in culture medium under different light intensities,and the relationship between expression of p-carotene biosynthesis-related genes and redox state of the photosynthetic electron transport chain was investigated.The main results were as follows.(1)A unicellular green alga was isolated and purified in samples with high salinity which collected from Hangu,Tianjin,China.Amplification,sequencing,sequence alignment,and phylogenetic tree alignment of internal transcribed spacer region(ITS)results indicated that the strain was D.salina.(2)Effects of seven different culture media on algal growth were compared,the growth curve showed that the modified Pick's medium was the most suitable for the growth of D.salina.Different concentrations of glucose,glycerol and sodium acetate were used for mixotrophic cultivation of D.salina.It was found that the most suitable concentration of glucose and glycerol for the growth of D.sali D.was 2 g/L.There were no significant differences in the effect of the concentration of sodium acetate on the growth of D.satina.The biomass in mixotrophic culture was lower than that of photoautotrophic culture.Similar results were also found in Nannochloropsis oceanica when cultured with the same carbon source.(3)Different light intensities(150-1500 ?mol photons·m-2s-1)were used in D.salina cultivation.The optimum intensity of light for algal growth was 600 ?mol photons·m-2s-1.With the increase of light intensity,the photosynthetic activity of photosystem ? and chlorophyll content decreased,the content of carotene increased.By transcriptome sequencing of algal cells under different light intensities,it was found that expression of genes encoding photosynthesis-related proteins was down-regulated under high light,while the expression of carotenoid and triacylglycerol biosynthesis-related genes was up-regulated.The reactive oxygen species(ROS)scavenging related genes and the xanthophyll cycle related genes were up-regulated.(4)Growth,carotene content and transcriptome of D.salina were compared under red(660 nm)and blue light(450 nm).Red light promoted the growth of D.salina cells,while blue light had no promoting effect on growth.Carotene accumulated under both red and blue light.The results of transcriptome showed that genes encoding for the photoreceptor(cryptochrome)and the carotenoid biosynthesis related enzymes were up-regulated under both red and blue light.Genes encoding for ROS scavenging enzymes were up-regulated under blue light,indicating that photoprotection mechanism was activated under blue light conditions.(5)The expression of carotenoid biosynthesis-related genes under different light intensities was investigated.Under high light,the carotenoid biosynthesis related genes:phytoene synthase,phytoene desaturase,?-carotene desaturase and lycopene?-cyclase were up-regulated.The content of p-carotene increased with the increase of light,however,expression of carotenoid biosynthesis-related genes did not increase.By adding the photosynthetic inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethyl urea under high light,the expression of carotenoid synthesis-related genes was down-regulated,while they were up-regulated by adding 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone.