Phylogenetic aspects of the sulfate assimilation genes from Thalassiosira pseudonana

Abstract

Diatoms are unicellular algae responsible for approximately 20 % of global carbon fixation. Their evolution by secondary endocytobiosis resulted in a complex cellular structure and metabolism compared to algae with primary plastids. In the last years the interest on unicellular algae increased. On the one hand assessments suggest that diatom-mediated export production can influence climate change through uptake and sequestration of atmospheric CO2. On the other hand diatoms are in focus because they are discussed as potential producer of biofuels. To follow the one or other idea it is necessary to investigate the diatoms biochemistry in order to understand the cellular regulatory mechanisms. The sulfur assimilation and methionine synthesis pathways provide S-containing amino acids for the synthesis of proteins and a range of metabolites such as dimethylsulfoniopropionate (DMSP) in order to provide basic metabolic precursors needed for the diatoms metabolism. To obtain an insight into the localization and organization of the sulfur metabolism pathways, the genome of Thalassiosira pseudonana-a model organism for diatom research-might help to understand the fundamental questions on adaptive responses of diatoms to dynamic environmental conditions such as nutrient availability in a broader context.

Nitrogen and sulfur assimilation in plants and algae

“…The redox insensitive ATP-S of Arabidopsis and that of Rhodophyta only contains 2 cysteines; 4 cysteines are present in Synechocystis PCC6803 and in most freshwater and marine cyanobacteria of genera different form Prochlorococcus and Synechococcus; in A. klebsii, five of the 6 cysteines in the ATP-S protein sequence are in different positions from those of the other eukaryotic algae (Giordano and Prioretti, 2014). The phylogeny of ATP-S was thoroughly described by Patron et al (2008): it is noteworthy that the genes encoding this enzymes in Arabidopsis have little sequence similarity with that of algae; the only exceptions are the sequences encoding the ATPS moieties of the fused ATP-S/APS kinase that are present in the genome of some haptophytes and heterokontophytes, which have a high degree of similarity with Arabidopsis ATP-S genes (Bromke et al, 2013;Giordano and Prioretti, 2014).…”

Diversity and regulation of ATP sulfurylase in photosynthetic organisms

“…Although biochemical and kinetic data are not yet available for this enzyme, it has been hypothesized that the pyrophosphatase removes the PPi produced as a by-product of APS synthesis, thereby making the forward ATPS reaction irreversible. For what it is known, the only diatom that appears to constitute an exception to this pattern of isoform localization is Thalassiosira pseudonana : in this species, based on the presence/absence of a plastid transit peptide and sequence analysis, it was suggested that the isoform with the sole ATPS domain is located in the cytosol, whereas the APK-ATPS-pyrophosphatase isoform is in the chloroplast (Patron et al, 2008; Bromke et al, 2013). This localization is however to be taken with care, since the sequence was inferred from a raw contig at a time when few protein models were available for T. pseudonana genome (N. J. Patron, personal communication); even now, currently available softwares for the prediction of signal/transit peptides are not optimized for secondary endosymbiotic organisms and we were unable to unambiguously determine the nature of this transit peptide.…”

Phylogenetic analysis of methionine synthesis genes from Thalassiosira pseudonana

“…The same is true for the exchange of metabolites between plastids and the cytoplasm. There is still little knowledge on the sulfur uptake and assimilation (Bromke and Hesse 2013 ; Kopriva et al 2008 ). To shed more light on the biosynthesis of methionine in the model diatom T. pseudonana , we have performed a detailed phylogenetic analysis of each enzyme from the methionine biosynthesis pathway in this organism.…”