Abstract
Viruses are considered key players in phytoplankton population control in oceans. However, mechanisms that control viral gene expression in prominent microalgae such as diatoms remain largely unknown. In this study, potential promoter regions isolated from several marine diatom-infecting viruses (DIVs) were linked to the egfp reporter gene and transformed into the Pennales diatom Phaeodactylum tricornutum. We analysed their activity in cells grown under different conditions. Compared to diatom endogenous promoters, novel DIV promoter (ClP1) mediated a significantly higher degree of reporter transcription and translation. Stable expression levels were observed in transformants grown under both light and dark conditions, and high levels of expression were reported in cells in the stationary phase compared to the exponential phase of growth. Conserved motifs in the sequence of DIV promoters were also found. These results allow the identification of novel regulatory regions that drive DIV gene expression and further examinations of the mechanisms that control virus-mediated bloom control in diatoms. Moreover, the identified ClP1 promoter can serve as a novel tool for metabolic engineering of diatoms. This is the first report describing a promoter of DIVs that may be of use in basic and applied diatom research.
Highlights
Viruses are considered key players in phytoplankton population control in oceans
To identify other regulatory sequences that are conserved amongst diatom-infecting viruses (DIVs) and endogenous promoters, we examined the frequency of consensus transcription factors (TFs) binding sites (TFBSs), which are available in the JASPAR database[55], through promoterome analyses[41] using oPOSSUM version 356
We tested viral promoter activity levels in diatom cells transformed with specific vectors, in which the viral promoter drove the expression of an enhanced green fluorescence protein (eGFP) reporter gene
Summary
Viruses are considered key players in phytoplankton population control in oceans. mechanisms that control viral gene expression in prominent microalgae such as diatoms remain largely unknown. Potential promoter regions isolated from several marine diatom-infecting viruses (DIVs) were linked to the egfp reporter gene and transformed into the Pennales diatom Phaeodactylum tricornutum. We analysed their activity in cells grown under different conditions. In some cases, diatom endogenous gene promoters drive species-specific transgene expression and do not function in different diatom species[18,20,22] These issues considerably limit the applications of diatom transformation techniques, potentially reducing the utility of diatoms in basic and applied research. Only a few reports focus on the transformation of diatoms through the use of CaMV 35S and CMV promoters[19,44] in P. tricornutum, and the same promoters do not seem to be effective in other species, such as the Centrics diatom Cyc. cryptica[19]
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