Abstract
The “UV sunscreen” compounds, the mycosporine-like amino acids (MAAs) are widely reported in cyanobacteria and are known to be induced under ultra-violet (UV) light. However, the impact of far red (FR) light on MAA biosynthesis has not been studied. We report results from two experiments measuring transcriptional regulation of MAA and aromatic amino acid pathways in the filamentous cyanobacterium Chlorogloeopsis fritschii PCC 6912. The first experiment, comparing UV with white light, shows the expected upregulation of the characteristic MAA mys gene cluster. The second experiment, comparing FR with white light, shows that three genes of the four mys gene cluster encoding up to mycosporine-glycine are also upregulated under FR light. This is a new discovery. We observed corresponding increases in MAAs under FR light using HPLC analysis. The tryptophan pathway was upregulated under UV, with no change under FR. The tyrosine and phenylalanine pathways were unaltered under both conditions. However, nitrate ABC transporter genes were upregulated under UV and FR light indicating increased nitrogen requirement under both light conditions. The discovery that MAAs are upregulated under FR light supports MAAs playing a role in photon dissipation and thermoregulation with a possible role in contributing to Earth surface temperature regulation.
Highlights
Cyanobacteria, the first evolutionary extant photosynthetic organisms, have evolved to adapt to a wide range of variable light environments and can survive exposure to both the ultraviolet (UV) and far-red (FR) ends of the visible light s pectrum[1,2]
The overall change in expression of genes in C. fritschii PCC 6912 exposed to UV-B and far red (FR) is shown in Fig. 1; this highlights the significant changes found associated with the mycosporine-like amino acids (MAAs) and aromatic amino acids (AAAs) pathways
MAAs are widely recognised as being important in photoprotection and AAAs are important in the synthesis of proteins and other essential end products
Summary
Cyanobacteria, the first evolutionary extant photosynthetic organisms, have evolved to adapt to a wide range of variable light environments and can survive exposure to both the ultraviolet (UV) and far-red (FR) ends of the visible light s pectrum[1,2]. Exposure to light at the FR end of the light spectrum has been shown to have an extensive acclimatory affect on the genome of cyanobacteria[2] Recognised for their UV sunscreening and photoprotection ability are a group of > 30 related low molecular weight aromatic amino acid derivatives called the MAAs. MAAs are a widely distributed in high-light marine, freshwater and terrestrial e nvironments[5,6]. As aromatic amino acid derivatives, MAAs have a core cyclohexenone or cyclohexenimine structure These have a methoxy group at C-2 position and substitution at C-3 with an amino acid or an imino alcohol giving the oxy-mycosporines such as mycosporine-glycine; a substition at C-1 with a second imino group leads to a wider group of imino-mycosporines including the commonly occuring shinorine. The mys cluster has been found to occur commonly across filamentous cyanobacteria[17]
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