Integrated Genomic and Transcriptomic Analysis of the Peridinin Dinoflagellate Amphidinium carterae Plastid.

The plastid genomes of peridinin-containing dinoflagellates are highly unusual, possessing very few genes, which are located on small chromosomal elements termed "minicircles". These minicircles may contain genes, or no recognisable coding information. Transcripts produced from minicircles may undergo unusual processing events, such as the addition of a 3' poly(U) tail. To date, little is known about the genetic or transcriptional diversity of non-coding sequences in peridinin dinoflagellate plastids. These sequences include empty minicircles, and regions of non-coding DNA in coding minicircles. Here, we present an integrated plastid genome and transcriptome for the model peridinin dinoflagellate Amphidinium carterae, identifying a previously undescribed minicircle. We also profile transcripts covering non-coding regions of the psbA and petB/atpA minicircles. We present evidence that antisense transcripts are produced within the A. carterae plastid, but show that these transcripts undergo different end cleavage events from sense transcripts, and do not receive 3' poly(U) tails. The difference in processing events between sense and antisense transcripts may enable the removal of non-coding transcripts from peridinin dinoflagellate plastid transcript pools.CNRS Investissements de l'avenir programme Gordon and Betty Moore Foundatio

Thiol redox switches regulate the oligomeric state of cyanobacterial Rre1, RpaA and RpaB response regulators.

Funder: Spicer Consulting LtdCyanobacteria employ two-component sensor-response regulator systems to monitor and respond to environmental challenges. The response regulators RpaA, RpaB, Rre1 and RppA are integral to circadian clock function and abiotic stress acclimation in cyanobacteria. RpaA, RpaB and Rre1 are known to interact with ferredoxin or thioredoxin, raising the possibility of their thiol regulation. Here, we report that Synechocystis sp. PCC 6803 Rre1, RpaA and RpaB exist as higher-order oligomers under oxidising conditions and that reduced thioredoxin A converts them to monomers. We further show that these response regulators contain redox-responsive cysteine residues with an Em7 around -300 mV. These findings suggest a direct thiol modulation of the activity of these response regulators, independent of their cognate sensor kinases

Adaptive laboratory evolution of the fast-growing cyanobacterium Synechococcus elongatus PCC 11801 for improved solvent tolerance.

Cyanobacteria hold promise as cell factories for the photoautotrophic conversion of carbon dioxide to useful chemicals. For the eventual commercial viability of such processes, cyanobacteria need to be engineered for (i) efficient channeling of carbon flux toward the product of interest and (ii) improved product tolerance, the latter being the focus of this study. We chose the recently reported, fast-growing, high light and CO2 tolerant cyanobacterium Synechococcus elongatus PCC 11801 for adaptive laboratory evolution. In two parallel experiments that lasted over 8400 h of culturing and 100 serial passages, S. elongatus PCC 11801 was evolved to tolerate 5 g/L n-butanol or 30 g/L 2,3-butanediol representing a 100% improvement in concentrations tolerated. The evolved strains retained alcohol tolerance even after being passaged several times without the alcohol stress suggesting that the changes were permanent. Whole genome sequencing of the n-butanol evolved strains revealed mutations in a number of stress responsive genes encoding translation initiation factors, RpoB and an ABC transporter. In 2,3-butanediol evolved strains, genes for ClpC, a different ABC transporter, glyceraldehyde-3-phosphate dehydrogenase and phosphoribulokinase were found to be mutated. Furthermore, the evolved strains showed significant improvement in tolerance toward several other alcohols. Notably, the n-butanol evolved strain could tolerate up to 32 g/L ethanol, thereby making it a promising host for photosynthetic production of biofuels via metabolic engineering