An endogenous microRNA (miRNA1166.1) can regulate photobio-H2 production in eukaryotic green alga Chlamydomonas reinhardtii

Small RNA-mediated silencing of phototropin suppresses the induction of photoprotection in the green alga Chlamydomonas reinhardtii

Small RNAs (sRNAs) form complexes with Argonaute proteins and bind to transcripts with complementary sequences to repress gene expression. sRNA-mediated regulation is conserved in a diverse range of eukaryotes and is involved in the control of various physiological functions. sRNAs are present in the unicellular green alga Chlamydomonas reinhardtii, and genetic analyses revealed that the core sRNA biogenesis and action mechanisms are conserved with those of multicellular organisms. However, the roles of sRNAs in this organism remain largely unknown. Here, we report that Chlamydomonas sRNAs contribute to the induction of photoprotection. In this alga, photoprotection is mediated by LIGHT HARVESTING COMPLEX STRESS-RELATED 3 (LHCSR3), whose expression is induced by light signals through the blue-light receptor phototropin (PHOT). We demonstrate here that sRNA-defective mutants showed increased PHOT abundance leading to greater LHCSR3 expression. Disruption of the precursor for two sRNAs predicted to bind to the PHOT transcript also increased PHOT accumulation and LHCSR3 expression. The induction of LHCSR3 in the mutants was enhanced by light containing blue wavelengths, but not by red light, indicating that the sRNAs regulate the degree of photoprotection via regulation of PHOT expression. Our results suggest that sRNAs are involved not only in the regulation of photoprotection but also in biological phenomena regulated by PHOT signaling.

Multiomics and optobiotechnological approaches for the development of microalgal strain for production of aviation biofuel and biorefinery

Demand and consumption of fossil fuels is increasing daily, and oil reserves are depleting. Technological developments are required towards developing sustainable renewable energy sources and microalgae are emerging as a potential candidate for various application-driven research. Molecular understanding attained through omics and system biology approach empowering researchers to modify various metabolic pathways of microalgal system for efficient extraction of biofuel and important biomolecules. This review furnish insight into different "advanced approaches" like optogenetics, systems biology and multi-omics for enhanced production of FAS (Fatty Acid Synthesis) and lipids in microalgae and their associated challenges. These new approaches would be helpful in the path of developing microalgae inspired technological platforms for optobiorefinery, which could be explored as source material to produce biofuels and other valuable bio-compounds on a large scale.

The regulatory activities of microRNAs in non-vascular plants: a mini review

MicroRNA-mediated gene regulation in non-vascular plants is potentially involved in several unique biological functions, including biosynthesis of several highly valuable exclusive bioactive compounds, and those small RNAs could be manipulated for the overproduction of essential bioactive compounds in the future. MicroRNAs (miRNAs) are a class of endogenous, small (20-24 nucleotides), non-coding RNA molecules that regulate gene expression through the miRNA-mediated mechanisms of either translational inhibition or messenger RNA (mRNA) cleavage. In the past years, studies have mainly focused on elucidating the roles of miRNAs in vascular plants as compared to non-vascular plants. However, non-vascular plant miRNAs have been predicted to be involved in a wide variety of specific biological mechanisms; nevertheless, some of them have been demonstrated explicitly, thus showing that the research field of this plant group owns a noteworthy potential to develop novel investigations oriented towards the functional characterization of these miRNAs. Furthermore, the insights into the roles of miRNAs in non-vascular plants might be of great importance for designing the miRNA-based genetically modified plants for valuable secondary metabolites, active compounds, and biofuels in the future. Therefore, in this current review, we provide an overview of the potential roles of miRNAs in different groups of non-vascular plants such as algae and bryophytes.

Advanced microalgae-based renewable biohydrogen production systems: A review

The reliance of fossil fuel for industrial and energy sectors has resulted in its depletion. Therefore, enormous efforts have been considered to move-out from fossil fuels to renewable energy sources based industrial process developments. Recently, biohydrogen (bio-H₂) has been recognised as a clean source of fuel with high-energy efficiency, which can be produced via different routes. Among them, biological fermentation processes are highly recommended due to eco-friendly and economically viable approaches compared to that of thermochemical processes. However, the low H₂ yield and high production cost are major bottlenecks for commercial scale operations. Thus, this review proposed an integrated microalgae-based H₂ production process, which will provides a possible route for commercialization in near future. Furthermore, process integration to improve efficiency and implementation of advanced strategies for the enhancement of bio-H₂ production, economic viability, and future research needs are discussed.

Recent advancement and strategy on bio-hydrogen production from photosynthetic microalgae

Recently, ensuring energy security is a key challenge to political and economic strength in the world. Bio-hydrogen production from microalgae is the promising alternative source for potential renewable and self-sustainability energy but still in the initial phase of development. Practically and sustainability of microalgae hydrogen production is still debatable. The genetic engineering and metabolic pathway engineering of hydrogenase and nitrogenase play a key role to enhance hydrogen production. Microalgae have photosynthetic efficiency and synthesize huge carbohydrate biomass, used as 4th generation feedstock to generate bio-hydrogen. Recent genetically modified strains of microalgae are the attractive source for enhancing bio-hydrogen production in the future. The potential of hydrogen production from microRNAs are gaining great interest of researcher. The main objective of this review is attentive discussed recent approaches on new molecular genetics engineering and metabolic pathway developments, modern photo-bioreactors efficiency, economic assessment, limitations and knowledge gap of bio-hydrogen production from microalgae.

Engineered Thermoanaerobacterium aotearoense with nfnAB knockout for improved hydrogen production from lignocellulose hydrolysates

BACKGROUND

As a renewable and clean energy carrier, the production of biohydrogen from low-value feedstock such as lignocellulose has increasingly garnered interest. The NADH-dependent reduced ferredoxin:NADP⁺ oxidoreductase (NfnAB) complex catalyzes electron transfer between reduced ferredoxin and NAD(P)⁺, which is critical for production of NAD(P)H-dependent products such as hydrogen and ethanol. In this study, the effects on end-product formation of deletion of nfnAB from Thermoanaerobacterium aotearoense SCUT27 were investigated.

RESULTS

Compared with the parental strain, the NADH/NAD⁺ ratio in the ∆nfnAB mutant was increased. The concentration of hydrogen and ethanol produced increased by (41.1 ± 2.37)% (p < 0.01) and (13.24 ± 1.12)% (p < 0.01), respectively, while the lactic acid concentration decreased by (11.88 ± 0.96)% (p < 0.01) when the ∆nfnAB mutant used glucose as sole carbon source. No obvious inhibition effect was observed for either SCUT27 or SCUT27/∆nfnAB when six types of lignocellulose hydrolysate pretreated with dilute acid were used for hydrogen production. Notably, the SCUT27/∆nfnAB mutant produced 190.63-209.31 mmol/L hydrogen, with a yield of 1.66-1.77 mol/mol and productivity of 12.71-13.95 mmol/L h from nonsterilized rice straw and corn cob hydrolysates pretreated with dilute acid.

CONCLUSIONS

The T. aotearoense SCUT27/∆nfnAB mutant showed higher hydrogen yield and productivity compared with those of the parental strain. Hence, we demonstrate that deletion of nfnAB from T. aotearoense SCUT27 is an effective approach to improve hydrogen production by redirecting the electron flux, and SCUT27/∆nfnAB is a promising candidate strain for efficient biohydrogen production from lignocellulosic hydrolysates.

Identification and Characterization of MiRNAs in Coccomyxa subellipsoidea C-169

Coccomyxa subellipsoidea C-169 (C-169) is an oleaginous microalga which is promising for renewable biofuel production. MicroRNAs (miRNAs), as the pivotal modulators of gene expression at post-transcriptional level, are prospective candidates for bioengineering practice. However, so far, no miRNA in C-169 has been reported and its potential impact upon CO₂ supplementation remains unclear. High-throughput sequencing of small RNAs from C-169 cultured in air or 2% CO₂ revealed 124 miRNAs in total, including 118 conserved miRNAs and six novel ones. In total, 384 genes were predicted as their potential target genes, 320 for conserved miRNAs and 64 for novel miRNAs. The annotated target genes were significantly enriched in six KEGG pathways, including pantothenate and CoA biosynthesis, C5-branched dibasic acid metabolism, 2-oxocarboxylic acid metabolism, butanoate metabolism, valine, leucine and isoleucine biosynthesis and alpha-linolenic acid metabolism. The miRNAs’ target genes were enriched in lipid metabolism as well as RNA-interacting proteins involved in translation, transcription and rRNA processing. The pioneering identification of C-169 miRNAs and analysis of their putative target genes lay the foundation for further miRNA research in eukaryotic algae and will contribute to the development of C-169 as an oleaginous microalga through bioengineering in the future.

Mechanisms of microRNA-mediated gene regulation in unicellular model alga Chlamydomonas reinhardtii

MicroRNAs are a class of endogenous non-coding RNAs that play a vital role in post-transcriptional gene regulation in eukaryotic cells. In plants and animals, miRNAs are implicated in diverse roles ranging from immunity against viral infections, developmental pathways, molecular pathology of cancer and regulation of protein expression. However, the role of miRNAs in the unicellular model green alga Chlamydomonas reinhardtii remains unclear. The mode of action of miRNA-induced gene silencing in C. reinhardtii is very similar to that of higher eukaryotes, in terms of the activation of the RNA-induced silencing complex and mRNA targeting. Certain studies indicate that destabilization of mRNAs and mRNA turnover could be the major possible functions of miRNAs in eukaryotic algae. Here, we summarize recent findings that have advanced our understanding of miRNA regulatory mechanisms in C. reinhardtii.