title: Both LOV1 and LOV2 domains of phototropin2 function as the photosensory domain for hypocotyl phototropic responses in Arabidopsis thaliana (Brassicaceae).
abstract: OBJECTIVE
  Phototropins (phot) are blue light receptor proteins that mediate phototropism and control photomovement responses, such as chloroplast photorelocation movement and stomatal opening. Arabidopsis thaliana has two phototropins, phot1 and phot2. Although both phot1 and phot2 redundantly mediate photomovement responses, phot2 uniquely regulates phototropism and the chloroplast avoidance response under high-intensity blue light. However, compared to that of phot1, the mechanistic basis of phot2 function is poorly understood, and in particular, the importance of the LOV2 domain in phot2 function has not been clearly demonstrated. Indeed, photocycle-deficient LOV2 transgenic lines expressing phot2 in a phot1phot2 mutant background retained phototropism, although with less sensitivity than wild-type plants.
  
  
  METHODS
  We isolated 11 alleles of phot2 mutants and determined the molecular lesion in each allele. We analyzed hypocotyl phototropism, chloroplast photorelocation movement, and leaf flattening in the phot2 mutant and the respective phot1phot2 double mutant plants.
  
  
  RESULTS
  We demonstrated that unlike the phot2 null mutant, the phot2-10 mutant, which has the defective phot2 LOV2 domain, retained the phototropic response and had unusual chloroplast movement. Mutants phot2-2 and phot2-6, which have a missense mutation in the kinase activation loop of phot2, had the phot2-null mutant phenotype. Furthermore, we convincingly demonstrated that the commonly used phot2-1 mutant allele is a phot2-null mutant.
  
  
  CONCLUSIONS
  The analyses of the multiple phot2 mutant alleles provided strong evidence for the importance of both LOV domains and the kinase activation loop of phot2 in phototropism and other phot-dependent responses and also demonstrated that phot2-1 allele is a null mutant.
authors.affiliation: Department of Biology, Faculty of Sciences, Kyushu University, Fukuoka 812-8581, Japan.
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Suetsugu
authors.forename: Sam-Geun
authors.initials: SG
authors.lastname: Kong
authors.forename: Masahiro
authors.initials: M
authors.lastname: Kasahara
authors.forename: Masamitsu
authors.initials: M
authors.lastname: Wada
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000378:metabolism*; D001483:Base Sequence; D002736:Chloroplasts / Q000378:metabolism; D005486:Flavin Mononucleotide / Q000378:metabolism; D018546:Hypocotyl / Q000502:physiology*; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D018524:Phototropism / Q000502:physiology*; D018515:Plant Leaves / Q000502:physiology; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D013057:Spectrum Analysis; D013329:Structure-Activity Relationship
chemical_list: D029681:Arabidopsis Proteins; D050505:Mutant Proteins; C423903:PHOT2 protein, Arabidopsis; D005486:Flavin Mononucleotide