title: Phototropin influence on eyespot development and regulation of phototactic behavior in Chlamydomonas reinhardtii.
abstract: The eyespot of Chlamydomonas reinhardtii is a light-sensitive organelle important for phototactic orientation of the alga. Here, we found that eyespot size is strain specific and downregulated in light. In a strain in which the blue light photoreceptor phototropin was deleted by homologous recombination, the light regulation of the eyespot size was affected. We restored this dysfunction in different phototropin complementation experiments. Complementation with the phototropin kinase fragment reduced the eyespot size, independent of light. Interestingly, overexpression of the N-terminal light, oxygen or voltage sensing domains (LOV1+LOV2) alone also affected eyespot size and phototaxis, suggesting that aside from activation of the kinase domain, they fulfill an independent signaling function in the cell. Moreover, phototropin is involved in adjusting the level of channelrhodopsin-1, the dominant primary receptor for phototaxis within the eyespot. Both the level of channelrhodopsin-1 at the onset of illumination and its steady state level during the light period are downregulated by phototropin, whereas the level of channelrhodopsin-2 is not significantly altered. Furthermore, a light intensity-dependent formation of a C-terminal truncated phototropin form was observed. We propose that phototropin is a light regulator of phototaxis that desensitizes the eyespot when blue light intensities increase.
authors.affiliation: Department of Biology, Friedrich-Alexander-University, 91058 Erlangen, Germany.
authors.forename: Jessica
authors.initials: J
authors.lastname: Trippens
authors.forename: Andre
authors.initials: A
authors.lastname: Greiner
authors.forename: Jana
authors.initials: J
authors.lastname: Schellwat
authors.forename: Martin
authors.initials: M
authors.lastname: Neukam
authors.forename: Theresa
authors.initials: T
authors.lastname: Rottmann
authors.forename: Yinghong
authors.initials: Y
authors.lastname: Lu
authors.forename: Suneel
authors.initials: S
authors.lastname: Kateriya
authors.forename: Peter
authors.initials: P
authors.lastname: Hegemann
authors.forename: Georg
authors.initials: G
authors.lastname: Kreimer
mesh_terms: D020418:Algal Proteins / Q000235:genetics / Q000378:metabolism; D016825:Chlamydomonas reinhardtii / Q000235:genetics / Q000254:growth & development / Q000502:physiology* / Q000528:radiation effects* / Q000648:ultrastructure; D015870:Gene Expression; D018506:Gene Expression Regulation, Plant / Q000528:radiation effects*; D005816:Genetic Complementation Test; D008027:Light; D009068:Movement / Q000502:physiology*; D053141:Organelle Size; D015388:Organelles / Q000502:physiology; D056949:Phototropins / Q000235:genetics / Q000378:metabolism*; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D017384:Sequence Deletion; D015398:Signal Transduction; D013045:Species Specificity
chemical_list: D020418:Algal Proteins; D056949:Phototropins; D011494:Protein Kinases