An Animal-Like Cryptochrome Controls the Chlamydomonas Sexual Cycle

Abstract

Cryptochromes are known as flavin-binding blue light receptors in bacteria, fungi, plants, and insects. The animal-like cryptochrome (aCRY) of the green alga has extended our view on cryptochromes, because it responds also to other wavelengths of the visible spectrum, including red light. Here, we have investigated if aCRY is involved in the regulation of the sexual life cycle of, which is controlled by blue and red light at the steps of gametogenesis along with its restoration and germination. We show that aCRY is differentially expressed not only during the life cycle but also within the cell as part of the soluble and/or membrane-associated protein fraction. Moreover, localization of aCRY within the algal cell body varies between vegetative cells and the different cell types of gametogenesis. aCRY is significantly (early day) or to a small extent (late night) enriched in the nucleus in vegetative cells. In pregametes, gametes and dark-inactivated gametes, aCRY is localized over the cell body. aCRY plays an important role in the sexual life cycle of : It controls the germination of the alga, under which the zygote undergoes meiosis, in a positive manner, similar to the regulation by the blue light receptors phototropin and plant cryptochrome (pCRY). However, aCRY acts in combination with pCRY as a negative regulator for mating ability as well as for mating maintenance, opposite to the function of phototropin in these processes.

Ultrafast Oxidation of a Tyrosine by Proton-Coupled Electron Transfer Promotes Light Activation of an Animal-like Cryptochrome

“…29 We found that this recombination is in competition with protonation of FAD •to form the neutral, red light-absorbing radical FADH • that is the primary target for CraCRY-based red light responses of Chlamydomonas cells. 21,22,104 The protonation was accelerated and hence more efficient at lower pH (see Figure S2D and SI, Section S2.2 for more details), explaining a previous observation 23 Remarkably, on a time scale up to a few nanoseconds, there are less losses by recombination in in the Y373F mutant protein (~20%) than in WT (~40%; Figures 3A and 3C). This may indicate that the .…”

“…In contrast to other cryptochromes, CraCRY appears to be capable of inducing a genetic response not only to blue, but also to red light. [20][21][22] This feature is probably related to another unique property of CraCRY, the very efficient formation and stabilization of its semireduced (red light-absorbing) flavin cofactor (FADH • ) that can be easily accumulated under blue light illumination and lives for seconds to minutes (depending on pH). 20,23 This process relies on the oxidation of the phenolic moiety of the tyrosine residue Y 373 as its mutation to phenylalanine abolishes this effect.…”

A Series of Fortunate Events: Introducing Chlamydomonas as a Reference Organism

“…The isolation and manipulation of zygotes are facilitated by plating mating mixtures on 4% agar plates, as zygotes adhere strongly to the surface of this medium. Zygotes are later induced to germinate (undergo meiosis) via transfer onto rich medium in the light, which is perceived by the blue light photoreceptors cryptochrome and phototropin (Huang and Beck, 2003;Müller et al, 2017;Zou et al, 2017). Chlamydomonas can be used for tetrad analysis via the dissection of the four germinated meiotic products, as they carry one or the other mating type, which segregate in a 2:2 ratio.…”

Bilin-Dependent Photoacclimation in Chlamydomonas reinhardtii

“…Among the genes associated with light sensing in Chlamydomonas, cryptochromes and phototropin appear to be obvious candidates to play roles in blue-light-dependent regulatory mechanisms (Huang et al, 2002;Zorin et al, 2009;Ahmad, 2016;Petroutsos et al, 2016;Duanmu et al, 2017Zou et al, 2017). Among the five genes encoding cryptochrome (CRY) photoreceptors (for a recent review on algal CRYs, see Duanmu et al, 2017;Kottke et al, 2017), expression levels for the gene encoding plant CRY (pCRY) are highest, peak in the dark, and are rapidly repressed upon the onset of light.…”