Phytoene synthase (PSY) as the key rate-limiting enzyme in carotenoid metabolism can be regulated by various regulators and factors. We found that DsPSY1 played a dominant role in carotenogenesis in the β-carotene-accumulating Dunaliella salina , and two amino acid residues critical in the substrate binding were associated with the functional variance between DsPSY1 and DsPSY2.

MADS transcription factors are involved in the regulation of fruit development and carotenoid metabolism in plants. However, whether and how carotenoid accumulation is regulated by algal MADS are largely unknown. In this study, we first used functional complementation to confirm the functional activity of phytoene synthase from the lutein‐rich Dunaliella sp. FACHB‐847 (DbPSY), the key rate‐limiting enzyme in the carotenoid biosynthesis. Promoters of DbPSY and DbLcyB (lycopene β‐cyclase) possessed multiple cis‐acting elements such as light‐, UV‐B‐, dehydration‐, anaerobic‐, and salt‐responsive elements, W‐box, and C‐A‐rich‐G‐box (MADS‐box). Meanwhile, we isolated one nucleus‐localized MADS transcription factor (DbMADS), belonging to type I MADS gene. Three carotenogenic genes, DbPSY, DbLcyB, and DbBCH (β‐carotene hydroxylase) genes were upregulated at later stages, which was well correlated with the carotenoid accumulation. In contrast, DbMADS gene was highly expressed at lag phase with low carotenoid accumulation. Yeast one‐hybrid assay and dual‐luciferase reporter assay demonstrated that DbMADS could directly bind to the promoters of two carotenogenic genes, DbPSY and DbLcyB, and repress their transcriptions. This study suggested that DbMADS may act as a negative regulator of carotenoid biosynthesis by repressing DbPSY and DbLcyB at the lag phase, which provide new insights into the regulatory mechanisms of carotenoid metabolism in Dunaliella.

As one of the sources of biodiesel, microalgae are expected to solve petroleum shortage. In this study, different concentrations of piperonyl butoxide were added to the culture medium to investigate their effects on the growth, pigment content, lipid accumulation, and content of carotenoids in Dunaliella tertiolecta. The results showed that piperonyl butoxide addition significantly decreased the biomass, chlorophyll content, and total carotenoid content but hugely increased the lipid accumulation. With the treatment of 150 ppm piperonyl butoxide combined with 8000 Lux light intensity, the final lipid accumulation and single-cell lipid content were further increased by 21.79 and 76.42% compared to those of the control, respectively. The lipid accumulation in D. tertiolecta is probably related to the increased expression of DtMFPα in D. tertiolecta under the action of piperonyl butoxide. The phylogenetic trees of D. tertiolecta and other oil-rich plants were constructed by multiple sequence alignment of DtMFPα, demonstrating their evolutionary relationship, and the tertiary structure of DtMFPα was predicted. In conclusion, piperonyl butoxide has a significant effect on lipid accumulation in D. tertiolecta, which provides valuable insights into chemical inducers to enhance biodiesel production in microalgae to solve the problem of diesel shortage.

Scope Dried Ziziphus jujuba Mill. kernel is a potential natural source of nutraceutical and therapeutic agents in China. Recent researches have shown that the saponins of dried Z. jujuba Mill. kernel (SZJs: SZJ‐1 and SZJ‐2) have various biological effects. However, the hypoglycemic activities and underlying mechanisms of SZJs remain obscure. Method and results In the current study, two saponins SZJ‐1 and SZJ‐2 mainly composed of betulinic acid, spinosin, jujuboside A, and jujuboside B are extracted and is olated from dried Z. jujuba Mill. kernel. The SZJ‐1 and SZJ‐2 could significantly inhibit the activities of digestion enzymes α‐glucosidase and α‐amylases. The hypoglycemic ability of SZJ‐1 and SZJ‐2 is further investigated and the results show that SZJ‐1 and SZJ‐2 can improve the hyperglycemic by increasing the glucose consumption, improving the superoxide dismutase (SOD), hexokinase (HK), pyruvate kinase (PK) activities, and decrease the MDA content of insulin resistant HepG2 cells. Furthermore, SZJ‐1 and SZJ‐2 can activate the phosphorated adenosine 5′‐monophosphate (AMP)‐activated protein kinase α (p‐AMPK), phosphoinositide 3‐kinase p110α (PI3K‐p110α), and phosphorated glycogen synthase kinase‐3β (Ser9) (p‐GSK3β). Conclusion These results indicating that the SZJ‐1 and SZJ‐2 might improve the insulin resistant symptoms by improving the energy metabolic level and increasing the glycogen synthase activity of HepG2 cells.