Cloning and Characterization of the Phytoene Desaturase(pds) Gene-a Key Enzyme for Carotenoids Synthesis in Dunaliella(Chlorophyta)

The unicellular green alga Dunaliella is outstanding for its ability of massive accumulation of carotenoids. To elucidate the carotenoids synthesis pathway in this alga,phytoene desaturase(pds) gene cDNA together with its DNA sequences were isolated and their structures and functions analyzed. The full-length pds cDNA of 2290 bp(GenBank Accession No. DQ243892) was de-duced from RACE results,including untranslated 21 bp 5'-and 520 bp 3'-flanking regions and an open reading frame of 582 amino acids,coding a protein of 64.196 kDa. The DNA sequence of 2908 bp(GenBank Accession No. DQ845248) including five introns was obtained. The fifth intron was uncompleted and complex,including two bases' perfect repeats(GT) 10 and large different-sized repeats within the last 400 bp. The Southern blot hybridization result demonstrated that this gene occurred as a single copy in this species,and the quantitative RT-PCR result showed that the transcription of this gene was constitutive. The evolutional significance of pds was discussed.

Proteomics Analysis of Lipid Droplets from the Oleaginous Alga Chromochloris zofingiensis Reveals Novel Proteins for Lipid Metabolism

Chromochloris zofingiensis represents an industrially relevant and unique green alga,given its capability of synthesizing triacylglycerol(TAG)and astaxanthin simultaneously for storage in lipid droplets(LDs).To further decipher lipid metabolism,the nitrogen deprivation(ND)-induced LDs from C.zofingiensis were isolated,purified,and subjected to proteomic analysis.Intriguingly,many C.zofingiensis LD proteins had no orthologs present in LD proteome of the model alga Chlamydomonas reinhardtii.Seven novel LD proteins(i.e.,two functionally unknown proteins,two caleosins,two lipases,and one L-gulonolactone oxidase)and the major LD protein(MLDP),which were all transcriptionally up-regulated by ND,were selected for further investigation.Heterologous expression in yeast demonstrated that all tested LD proteins were localized to LDs and all except the two functionally unknown proteins enabled yeast to produce more TAG.MLDP could restore the phenotype of mldp mutant strain and enhance TAG synthesis in wildtype strain of C.reinhardtii.Although MLDP and caleosins had a comparable abundance in LDs,they responded distinctly to ND at the transcriptional level.The two lipases,instead of functioning as TAG lipases,likely recycled polar lipids to support TAG synthesis.For the first time,we reported that L-gulonolactone oxidase was abundant in LDs and facilitated TAG accumulation.Moreover,we also proposed a novel working model for C.zofingiensis LDs.Taken together,our work unravels the unique characteristics of C.zofingiensis LDs and provides insights into algal LD biogenesis and TAG synthesis,which would facilitate genetic engineering of this alga for TAG improvement.

Methane production from Sargassum muticum:effects of seasonality and of freshwater washes

Biogas production from Sargassum muticum,an invasive seaweed species to Europe,is hampered by low methane(CH_(4))yields during anaerobic digestion(AD),but causes are unclear.This research is the first to demonstrate the impact of extensive freshwater washing of spring-and summer-harvested S.muticum on the CH_(4)production rates and the biochemical methane potential(BMP).The findings reveal that the rate profile of CH_(4)production is affected by extensively washing the seaweed and is dependent on seasonality.Spring-harvested S.muticum had higher initial CH_(4)production rates compared to summer-harvested S.muticum.For spring-harvested S.muticum,the initial rate of CH_(4)production was lowered by extensive washing.In contrast,extensively washed summer-harvested S.muticum had a higher degradation rate and CH_(4)production rate relative to its non-extensively washed counterpart.The highest CH_(4)potentials accumulated by the treated and non-treated S.muticum are,however,statistically similar and not influenced by seasonality or extensive washing(p>0.05).Potential causes for differences in the rate of CH_(4)production between summer-and spring-harvested S.muticum are discussed.The differences in CH_(4)production from treated summer-and spring-harvested S.muticum acts as a stepping stone to understanding the causes for low CH_(4)yields,which could allow for further enhancements in CH_(4)production from S.muticum.