Bioinformatics evidence for the transfer of mycosporine-like amino acid core (4-deoxygadusol) synthesizing gene from cyanobacteria to dinoflagellates and an attempt to mutate the same gene (YP_324358) in Anabaena variabilis PCC 7937

Effects of nitrate on the saxitoxins biosynthesis revealed by sxt genes in the toxic dinoflagellate Alexandrium pacificum (group IV)

The dinoflagellate Alexandrium pacificum (group IV) is of particular interest because of its involvement in harmful algal blooms and production of saxitoxin (STX), which causes paralytic shellfish poisoning. The toxicity from STX and its analogues (STXs) is suspected to be affected by nitrogen (N) availability. However, the toxicity-associated behavior and STX-biosynthesis gene responses of the toxic A. pacificum under N fluctuations have not been sufficiently investigated. In the present study, we identified the sxtI gene involved in sxt biosynthesis pathway and evaluated the effects of nitrate (NO3-) on STXs production and the expression of four sxt core genes (sxtA4, sxtG, sxtB, and sxtI). Quantification of total STXs levels in the cultures under different NO3- regimes showed that NO3- concentration influenced STXs production. In addition, the proportion and concentration of STXs varied depending on the NO3- concentration. Core sxt transcript abundance was also influenced by available NO3- in a time-dependent manner. Expressional levels and patterns of sxtI were correlated with those of sxtA and sxtB. The relationship between the toxins and sxt responses in A. pacificum under various NO3- regimes suggests the direct involvement of N in the STXs biosynthesis pathway. Understanding this link would provide a tool to understand the toxin dynamics of dinoflagellates following N shifts in marine environments.

The sedoheptulose 7-phosphate cyclases and their emerging roles in biology and ecology

Covering up to: 1999-2016This highlight covers a family of enzymes of growing importance, the sedoheptulose 7-phosphate cyclases, initially of interest due to their involvement in the biosynthesis of pharmaceutically relevant secondary metabolites. More recently, these enzymes have been found throughout Prokarya and Eukarya, suggesting their broad potential biological roles in nature.

Flavonoids and Melanins: a common strategy across two kingdoms

Ultraviolet (UV) radiations alter a number of metabolic functions in vivant. They produce damages to lipids, nucleic acids and proteins, generating reactive oxygen species such as singlet oxygen (O₂), hydroxyl radical (HO) and superoxide anion (O₂^-). Plants and animals, after their water emersion, have developed biochemical mechanisms to protect themselves from that environmental threat through a common strategy. Melanins in animals and flavonoids in plants are antioxidant pigments acting as free radical scavenging mechanisms. Both are phenol compounds constitutively synthesized and enhanced after exposure to UV rays, often conferring a red-brown-dark tissue pigmentation.

Noteworthy, beside anti-oxidant scavenging activity, melanins and flavonoids have acquired secondary functions that, both in plants and animals, concern reproductions and fitness. Plants highly pigmented are more resistant to biotic and abiotic stresses. Darker wild vertebrates are generally more aggressive, sexually active and resistant to stress than lighter individuals. Flavonoids have been associated with signal attraction between flowers and insects and with plant-plant interaction. Melanin pigmentation has been proposed as trait in bird communication, acting as honest signals of quality.

This review shows how the molecular mechanisms leading to tissue pigmentation have many functional analogies between plants and animals and how their origin lies in simpler organisms such as Cyanobacteria. Comparative studies between plant and animal kingdoms can reveal new insight of the antioxidant strategies in vivant.

Identification and upregulation of biosynthetic genes required for accumulation of Mycosporine-2-glycine under salt stress conditions in the halotolerant cyanobacterium Aphanothece halophytica

Mycosporine-like amino acids (MAAs) are valuable molecules that are the basis for important photoprotective constituents. Here we report molecular analysis of mycosporine-like amino acid biosynthetic genes from the halotolerant cyanobacterium Aphanothece halophytica, which can survive at high salinity and alkaline pH. This extremophile was found to have a unique MAA core (4-deoxygadusol)-synthesizing gene separated from three other genes. In vivo analysis showed accumulation of the mycosporine-2-glycine but not shinorine or mycosporine-glycine. Mycosporine-2-glycine accumulation was stimulated more under the stress condition of high salinity than UV-B radiation. The Aphanothece MAA biosynthetic genes also manifested a strong transcript level response to salt stress. Furthermore, the transformed Escherichia coli and Synechococcus strains expressing four putative Aphanothece MAA genes under the control of a native promoter were found to be capable of synthesizing mycosporine-2-glycine. The accumulation level of mycosporine-2-glycine was again higher under the high-salinity condition. In the transformed E. coli cells, its level was approximately 85.2 ± 0.7 μmol/g (dry weight). Successful production of a large amount of mycosporine in these cells provides a new opportunity in the search for an alternative natural sunscreen compound source.

Evolution and distribution of saxitoxin biosynthesis in dinoflagellates

Numerous species of marine dinoflagellates synthesize the potent environmental neurotoxic alkaloid, saxitoxin, the agent of the human illness, paralytic shellfish poisoning. In addition, certain freshwater species of cyanobacteria also synthesize the same toxic compound, with the biosynthetic pathway and genes responsible being recently reported. Three theories have been postulated to explain the origin of saxitoxin in dinoflagellates: The production of saxitoxin by co-cultured bacteria rather than the dinoflagellates themselves, convergent evolution within both dinoflagellates and bacteria and horizontal gene transfer between dinoflagellates and bacteria. The discovery of cyanobacterial saxitoxin homologs in dinoflagellates has enabled us for the first time to evaluate these theories. Here, we review the distribution of saxitoxin within the dinoflagellates and our knowledge of its genetic basis to determine the likely evolutionary origins of this potent neurotoxin.