title: Reduced phototropism in pks mutants may be due to altered auxin-regulated gene expression or reduced lateral auxin transport.
abstract: Phototropism allows plants to orient their photosynthetic organs towards the light. In Arabidopsis, phototropins 1 and 2 sense directional blue light such that phot1 triggers phototropism in response to low fluence rates, while both phot1 and phot2 mediate this response under higher light conditions. Phototropism results from asymmetric growth in the hypocotyl elongation zone that depends on an auxin gradient across the embryonic stem. How phototropin activation leads to this growth response is still poorly understood. Members of the phytochrome kinase substrate (PKS) family may act early in this pathway, because PKS1, PKS2 and PKS4 are needed for a normal phototropic response and they associate with phot1 in vivo. Here we show that PKS proteins are needed both for phot1- and phot2-mediated phototropism. The phototropic response is conditioned by the developmental asymmetry of dicotyledonous seedlings, such that there is a faster growth reorientation when cotyledons face away from the light compared with seedlings whose cotyledons face the light. The molecular basis for this developmental effect on phototropism is unknown; here we show that PKS proteins play a role at the interface between development and phototropism. Moreover, we present evidence for a role of PKS genes in hypocotyl gravi-reorientation that is independent of photoreceptors. pks mutants have normal levels of auxin and normal polar auxin transport, however they show altered expression patterns of auxin marker genes. This situation suggests that PKS proteins are involved in auxin signaling and/or lateral auxin redistribution.
authors.affiliation: Center for Integrative Genomics, Faculty of Biology and Medicine, University of Lausanne, Genopode Building, 1015, Lausanne, Switzerland.
authors.forename: Chitose
authors.initials: C
authors.lastname: Kami
authors.forename: Laure
authors.initials: L
authors.lastname: Allenbach
authors.forename: Melina
authors.initials: M
authors.lastname: Zourelidou
authors.forename: Karin
authors.initials: K
authors.lastname: Ljung
authors.forename: Frédéric
authors.initials: F
authors.lastname: Schütz
authors.forename: Erika
authors.initials: E
authors.lastname: Isono
authors.forename: Masaaki K
authors.initials: MK
authors.lastname: Watahiki
authors.forename: Kotaro T
authors.initials: KT
authors.lastname: Yamamoto
authors.forename: Claus
authors.initials: C
authors.lastname: Schwechheimer
authors.forename: Christian
authors.initials: C
authors.lastname: Fankhauser
mesh_terms: D017360:Arabidopsis / Q000166:cytology / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport; D016000:Cluster Analysis; D018506:Gene Expression Regulation, Plant; D017930:Genes, Reporter; D018546:Hypocotyl / Q000166:cytology / Q000235:genetics / Q000502:physiology / Q000528:radiation effects; D007210:Indoleacetic Acids / Q000032:analysis / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D008027:Light; D008565:Membrane Proteins; D009154:Mutation; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D018524:Phototropism; D010834:Phytochrome / Q000032:analysis / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D036226:Seedlings / Q000166:cytology / Q000235:genetics / Q000502:physiology / Q000528:radiation effects; D015398:Signal Transduction
chemical_list: D029681:Arabidopsis Proteins; D007210:Indoleacetic Acids; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; C485609:PKS1 protein, Arabidopsis; C502023:PKS2 protein, Arabidopsis; D010750:Phosphoproteins; D010834:Phytochrome; C512593:PKS4 protein, Arabidopsis; D017346:Protein Serine-Threonine Kinases
keywords: Arabidopsis thaliana; auxin; phototropin 1; phototropism; phytochrome kinase substrate