Functional characterization of Chlamydomonas reinhardtii with alterations in the atpE gene

Genetic engineering for biohydrogen production from microalgae

The development of biohydrogen as an alternative energy source has had great economic and environmental benefits. Hydrogen production from microalgae is considered a clean and sustainable energy production method that can both alleviate fuel shortages and recycle waste. Although algal hydrogen production has low energy consumption and requires only simple pretreatment, it has not been commercialized because of low product yields. To increase microalgal biohydrogen production several technologies have been developed, although they struggle with the oxygen sensitivity of the hydrogenases responsible for hydrogen production and the complexity of the metabolic network. In this review, several genetic and metabolic engineering studies on enhancing microalgal biohydrogen production are discussed, and the economic feasibility and future direction of microalgal biohydrogen commercialization are also proposed.

Comparative analyses of 32 complete plastomes of Tef (Eragrostis tef ) accessions from Ethiopia: phylogenetic relationships and mutational hotspots

Eragrostis tef is an important cereal crop in Ethiopia with excellent storage properties, high–quality food, and the unique ability to thrive in extreme environmental conditions. However, the application of advanced molecular tools for breeding and conservation of these species is extremely limited. Therefore, developing chloroplast genome resources and high-resolution molecular markers are valuable to E. tef population and biogeographic studies. In the current study, we assembled and compared the complete plastomes of 32 E. tef accessions. The size of the plastomes ranged from 134,349 to 134,437 bp with similar GC content (∼38.3%). Genomes annotations revealed 112 individual genes, including 77 protein-coding, 31 tRNA, and 4 rRNA genes. Comparison of E. tef plastomes revealed a low degree of intraspecific sequence variations and no structural differentiations. Furthermore, we found 34 polymorphic sites (13 cpSSRs, 12 InDels, and 9 SNPs) that can be used as valuable DNA barcodes. Among them, the majority (88%) of the polymorphic sites were identified in the noncoding genomic regions. Nonsynonymous (ka) and synonymous (ks) substitution analysis showed that all PCGs were under purifying selection (ka/ks <1). The phylogenetic analyses of the whole plastomes and polymorphic region sequences were able to distinguish the accession from the southern population, indicating its potential to be used as a super-barcode. In conclusion, the newly generated plastomes and polymorphic markers developed here could be a useful genomic resource in molecular breeding, population genetics and the biogeographical study of E. tef.

Potential involvement of N-terminal acetylation in the quantitative regulation of the ε subunit of chloroplast ATP synthase under drought stress

In plants, modulation of photosynthetic energy conversion in varying environments is often accompanied by adjustment of the abundance of photosynthetic components. In wild watermelon (Citrullus lanatus L.), proteome analysis revealed that the ε subunit of chloroplast ATP synthase occurs as two distinct isoforms with largely-different isoelectric points, although encoded by a single gene. Mass spectrometry (MS) analysis of the ε isoforms indicated that the structural difference between the ε isoforms lies in the presence or absence of an acetyl group at the N-terminus. The protein level of the non-acetylated ε isoform preferentially decreased in drought, whereas the abundance of the acetylated ε isoform was unchanged. Moreover, metalloprotease activity that decomposed the ε subunit was detected in a leaf extract from drought-stressed plants. Furthermore, in vitro assay suggested that the non-acetylated ε subunit was more susceptible to degradation by metalloaminopeptidase. We propose a model in which quantitative regulation of the ε subunit involves N-terminal acetylation and stress-induced proteases.

Altered expression of the chloroplast ATP synthase through site-directed mutagenesis in Chlamydomonas reinhardtii

The chloroplast ATP synthase gates the flow of protons out of the thylakoid lumen. In Chlamydomonas reinhardtii deletion of any of the genes for the ATP synthase subunits, or misfolding of the peptides results in photosynthetic membranes devoid of the enzyme (Lemaire and Wollman, J Biol Chem 264:675-685, 1989). This work examines the physiologic response of an algal strain in which the epsilon subunit of the chloroplast ATP synthase has been truncated. Removal of 10 amino acids from the C-terminus of the peptide results in a sharp decrease in the content of the enzyme, but does not result in its exclusion from the thylakoid membranes. The ATP synthase of this mutant strain has a higher rate of ATP hydrolysis than the wild-type enzyme. This strain of C. reinhardtii exhibits reduced growth in the light, dependence on acetate, and a low threshold for the onset of photoinhibition. The role of the ATP synthase in regulating the proton concentration of the lumen is discussed.

Ultrahigh bioproductivity from algae

The potential for dramatic increases in bioproductivity in algal photobioreactors relative to current biomass approaches, e.g., for converting sunlight into biofuels, by an unorthodox integration of photonics and biotechnologies is described. The key to greater biomass yields--projected as high as 100 g dry weight m(-2) h(-1)-is a pronounced heightening of algal flux tolerance, achieved by tailoring the photonic temporal, spectral and intensity characteristics with pulsed light-emitting diodes. Such tailored photonic input is applied in concert with thin-channel ultradense culture photobioreactors with flow patterns that produce rapid light/dark algae exposure cycles. The artificial-light scheme is globally feasible only with electricity generated from renewables. Recent advances in ultra-efficient concentrator photovoltaics, as well as high-performance light-emitting diodes, create a practical reality for converting sunlight into pulsed red light and delivering it to indoor photobioreactors, with characteristic pulse times and intensities optimally suited to the rate-limiting dark reactions of photosynthesis. Cellular engineering built upon recent progress in modifying algal chlorophyll antenna size, in combination with metabolic engineering, could further enhance bioproductivity. The proposed strategy requires no major advances for implementation and adopts existing technologies.

Expression by Chlamydomonas reinhardtii of a chloroplast ATP synthase with polyhistidine-tagged beta subunits

The green alga Chlamydomonas reinhardtii is a model organism for the study of photosynthesis. The chloroplast ATP synthase is responsible for the synthesis of ATP during photosynthesis. Using genetic engineering and biolistic transformation, a string of eight histidine residues has been inserted into the amino-terminal end of the beta subunit of this enzyme in C. reinhardtii. The incorporation of these amino acids did not impact the function of the ATP synthase either in vivo or in vitro and the resulting strain of C. reinhardtii showed normal growth. The addition of these amino acids can be seen through altered gel mobility of the beta subunit and the binding of a polyhistidine-specific dye to the subunit. The purified his-tagged CF1 has normal Mg(2+)-ATPase activity, which can be stimulated by alcohol and detergents and the enzyme remains active while bound to a nickel-coated surface. Potential uses for this tagged enzyme as a biochemical tool are discussed.