Improved photobio-H2 production regulated by artificial miRNA targeting psbA in green microalga Chlamydomonas reinhardtii

Abstract

BackgroundSulfur-deprived cultivation of Chlamydomonas reinhardtii, referred as “two-stage culture” transferring the cells from regular algal medium to sulfur-deplete one, has been extensively studied to improve photobio-H2 production in this green microalga. During sulfur-deprivation treatment, the synthesis of a key component of photosystem II complex, D1 protein, was inhibited and improved photobio-H2 production could be established in C. reinhardtii. However, separation of algal cells from a regular liquid culture medium to a sulfur-deprived one is not only a discontinuous process, but also a cost- and time-consuming operation. More applicable and economic alternatives for sustained H2 production by C. reinhardtii are still highly required.ResultsIn the present study, a significant improvement in photobio-H2 production was observed in the transgenic green microalga C. reinhardtii, which employed a newly designed strategy based on a heat-inducible artificial miRNA (amiRNA) expression system targeting D1-encoded gene, psbA. A transgenic algal strain referred as “amiRNA-D1” has been successfully obtained by transforming the expression vector containing a heat-inducible promoter. After heat shock conducted in the same algal cultures, the expression of amiRNA-D1 was detected increased 15-fold accompanied with a 73% decrease of target gene psbA. More interestingly, this transgenic alga accumulated about 60% more H2 content than the wild-type strain CC-849 at the end of 7-day cultivation.ConclusionsThe photobio-H2 production in the engineered transgenic alga was significantly improved. Without imposing any nutrient-deprived stress, this novel strategy provided a convenient and efficient way for regulation of photobio-H2 production in green microalga by simply “turn on” the expression of a designed amiRNA.Electronic supplementary materialThe online version of this article (10.1186/s13068-018-1030-2) contains supplementary material, which is available to authorized users.

Biohydrogen from Microalgae: Production and Applications

“…In Chlamydomonas reinhardtii, some endogenous miRNAs have overexpressed in S deprivation conditions. These observations led to the design of several artificial miRNAs (amiRNAs) to increase hydrogen yields by stimulating a faster oxygen consumption or repressing psbA gene expression that encodes for PSII linked D1 protein [47,48]. Similarly, optogenetic systems have also developed using properly blue light-inducible expression amiRNAs.…”

Plastid terminal oxidases in Chlamydomonas: connections with astaxanthin and bio-hydrogen production

“…Sulfur-deprived cultivation of C. reinhardtii [52] was previously regarded as the most efficient technique to enhance photobio-H 2 production in microalgae [53][54][55]. Most recently, modification of photosynthetic genes and even non-coding RNAs in Chlamydomonas significantly improve the bio-hydrog8 en production [35,56,57].…”

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

“…Afterwards, a blue light-inducible system was constructed to optogenetically regulate an amiRNA (amiR-D1) and, consequently, regulation of its target gene. Hydrogen production was enhanced in Chlamydomonas using this system [ 133 , 134 ]. In addition, using amiRNA to inhibit the phosphoenolpyruvate carboxylase increased fatty acid production in a green microalga Chlamydomonas [ 133 ].…”

“…Some encouraging results have been reported, for instance, endogenous miRNA showed promising regulatory roles on H 2 production in C. reinhardtii [ 138 ]. In addition, by artificial miRNAs we achieved successfully to regulate the productions of H 2 , fatty acid and carotenoids [ 133 , 134 , 139 – 143 ]. Understanding the mechanism of action of miRNAs in C. reinhardtii is of great significance to further utilize microalgae as biofuel- or bioproduct-based resources.…”