A novel cryptochrome in the diatom Phaeodactylum tricornutum influences the regulation of light‐harvesting protein levels

Abstract

Diatoms possess several genes for proteins of the cryptochrome/photolyase family. A typical sequence for a plant cryptochrome was not found in our analysis of the Phaeodactylum tricornutum genome, but one protein grouped with higher plant and green algal cryptochromes. This protein, CryP, binds FAD and 5,10-methenyltetrahydrofolate, according to our spectroscopic studies on heterologously expressed protein. 5,10-Methenyltetrahydrofolate binding is a feature common to both cyclobutane pyrimidine dimer photolyases and DASH cryptochromes. In recombinant CryP, however, the FAD chromophore was present in its neutral radical state and had a red-shifted absorption maximum at 637 nm, which is more characteristic for a DASH cryptochrome than a cyclobutane pyrimidine dimer photolyase. Upon illumination with blue light, the fully reduced state of FAD was formed in the presence of reductant. Expression of CryP was silenced by antisense approaches, and the resulting cell lines showed increased levels of proteins of light-harvesting complexes, the Lhcf proteins, in vivo. In contrast, the levels of proteins active in light protection, the Lhcx proteins, were reduced. Thus, CryP cannot be directly grouped with known members of the cryptochrome/photolyase family. Of all P. tricornutum proteins, it is the most similar in sequence to a plant cryptochrome, and is involved in the regulation of light-harvesting protein expression, but shows spectroscopic features and a chromophore composition that are most typical of a DASH cryptochrome.

Residues at a Single Site Differentiate Animal Cryptochromes from Cyclobutane Pyrimidine Dimer Photolyases by Affecting the Proteins' Preferences for Reduced FAD

“…in WT at 584 nm and 623 nm were red‐shifted to 588 nm and 630–632 nm, respectively, in A377I, A377L, and A377V (Figure B). Similar red shifts were also observed in eukaryotic (6–4) photolyases of A. thaliana and Xenopus laevis , Ostreococcus tauri OtCPF1, and a novel cryptochrome CryP of Phaeodactylum tricornutum , which have Ile, Leu, Leu, and Ile at site 377, respectively. In contrast, the absorption peaks of FADH .…”

“…To obtain time‐dependent concentrations of E‐FADH − , E‐FADH . , E‐FAD ox , and free FAD ox in solution for each protein, spectra between 340 and 700 nm were fitted by the multiple linear regression method using the molar extinction coefficient spectra for the four components listed in Figure S3 as independent data. An intercept was included to adjust small absorbance offsets.…”

The diatom Phaeodactylum tricornutum adjusts nonphotochemical fluorescence quenching capacity in response to dynamic light via fine‐tuned Lhcx and xanthophyll cycle pigment synthesis

“…In line with this, the Lhcx1 gene promoter has a binding motif for a blue light receptor, aureochrome 1a (Schellenberger Costa et al ., ). The cryptochromes CPF (Coesel et al ., ) and CryP (Juhas et al ., ) regulate expression of Lhcx genes. Interestingly, in Chlamydomonas reinhardtii the cryptochrome aCRY, which is related to CryP, seems to react on light intensity rather than on light quality (Beel et al ., ), and hence CryP could modulate NPQ capacity in diatoms in response to different light intensities.…”

Delocalized hole transport coupled to sub-ns tryptophanyl deprotonation promotes photoreduction of class II photolyases

“…† The evolutionary links between the different members of the photolyase and cryptochrome superfamily (PCSf) may be found in various reports [7][8][9][10]. …”