Phototropin LOV domains exhibit distinct roles in regulating photoreceptor function.
Phototropins (phot1 and phot2) are autophosphorylating serine/threonine kinases that function as photoreceptors for phototropism, light-induced chloroplast movement, and stomatal opening in Arabidopsis. The N-terminal region of phot1 and phot2 contains two specialized PAS domains, designated LOV1 and LOV2, which function as binding sites for the chromophore flavin mononucleotide (FMN). Both LOV1 and LOV2 undergo a self-contained photocycle, which involves the formation of a covalent adduct between the FMN chromophore and a conserved active-site cysteine residue (Cys39). Replacement of Cys39 with alanine abolishes the light-induced photochemical reaction of LOV1 and LOV2. Here we have used the Cys39Ala mutation to investigate the role of LOV1 and LOV2 in regulating phototropin function. Photochemical analysis of a bacterially expressed LOV1 + LOV2 fusion protein indicates that LOV2 functions as the predominant light-sensing domain for phot1. LOV2 also plays a major role in mediating light-dependent autophosphorylation of full-length phot1 expressed in insect cells and transgenic Arabidopsis. Moreover, photochemically active LOV2 alone in full-length phot1 is sufficient to elicit hypocotyl phototropism in transgenic Arabidopsis, whereas photochemically active LOV1 alone is not. Further photochemical and biochemical analyses also indicate that the LOV1 and LOV2 domains of phot2 exhibit distinct roles. The significance for the different roles of the phototropin LOV domains is discussed.
Christie
John M
JM
Department of Plant Biology, Carnegie Institution of Washington, Stanford, California 94305, USA.
Swartz
Trevor E
TE
Bogomolni
Roberto A
RA
Briggs
Winslow R
WR
D000818:Animals; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D001419:Bacteria / Q000235:genetics; D001665:Binding Sites; D056931:Cryptochromes; D003545:Cysteine / Q000235:genetics; D029721:Drosophila Proteins; D005136:Eye Proteins; D005486:Flavin Mononucleotide / Q000378:metabolism; D005420:Flavoproteins / Q000235:genetics / Q000378:metabolism*; D005453:Fluorescence; D005786:Gene Expression Regulation / Q000528:radiation effects; D018546:Hypocotyl / Q000378:metabolism / Q000528:radiation effects; D007313:Insecta / Q000166:cytology / Q000235:genetics; D008027:Light; D009154:Mutation; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D010777:Photochemistry; D017956:Photoreceptor Cells, Invertebrate; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism* / Q000528:radiation effects; D018524:Phototropism; D030821:Plants, Genetically Modified; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D043562:Receptors, G-Protein-Coupled; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism
D029681:Arabidopsis Proteins; C538962:CRY1 protein, Arabidopsis; D056931:Cryptochromes; D029721:Drosophila Proteins; D005136:Eye Proteins; D005420:Flavoproteins; C423903:PHOT2 protein, Arabidopsis; D010750:Phosphoproteins; D045322:Photosynthetic Reaction Center Complex Proteins; D043562:Receptors, G-Protein-Coupled; D011993:Recombinant Fusion Proteins; C119828:cry protein, Drosophila; D005486:Flavin Mononucleotide; C103646:NPH1 protein, Arabidopsis; D017346:Protein Serine-Threonine Kinases; D003545:Cysteine