Defining the site of light perception and initiation of phototropism in Arabidopsis.
Phototropism is an adaptive response allowing plants to optimize photosynthetic light capture. This is achieved by asymmetric growth between the shaded and lit sides of the stimulated organ. In grass seedlings, the site of phototropin-mediated light perception is distinct from the site of bending; however, in dicotyledonous plants (e.g., Arabidopsis), spatial aspects of perception remain debatable. We use morphological studies and genetics to show that phototropism can occur in the absence of the root, lower hypocotyl, hypocotyl apex, and cotyledons. Tissue-specific expression of the phototropin1 (phot1) photoreceptor demonstrates that light sensing occurs in the upper hypocotyl and that expression of phot1 in the hypocotyl elongation zone is sufficient to enable a normal phototropic response. Moreover, we show that efficient phototropism occurs when phot1 is expressed from endodermal, cortical, or epidermal cells and that its local activation rapidly leads to a global response throughout the seedling. We propose that spatial aspects in the steps leading from light perception to growth reorientation during phototropism differ between grasses and dicots. These results are important to properly interpret genetic experiments and establish a model connecting light perception to the growth response, including cellular and morphological aspects.
Centre for Integrative Genomics, Faculty of Biology and Medicine, University of Lausanne, 1015 Lausanne, Switzerland.
Tobias
T
Preuten
Tim
T
Hohm
Sven
S
Bergmann
Christian
C
Fankhauser
D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D018548:Cotyledon / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D000077614:Golgi Matrix Proteins; D018398:Homeodomain Proteins / Q000235:genetics; D018546:Hypocotyl / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D010750:Phosphoproteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D018524:Phototropism / Q000235:genetics* / Q000502:physiology*; D018517:Plant Roots / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics; D036226:Seedlings / Q000235:genetics / Q000378:metabolism; D012639:Seeds / Q000378:metabolism; D015398:Signal Transduction
C103790:ATML1 protein, Arabidopsis; D029681:Arabidopsis Proteins; C510310:CAB3 protein, Arabidopsis; C504617:CASP protein, Arabidopsis; D000077614:Golgi Matrix Proteins; D018398:Homeodomain Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; C423903:PHOT2 protein, Arabidopsis; D010750:Phosphoproteins; C100978:SCR protein, Arabidopsis; C405165:PINOID protein, Arabidopsis; C103646:NPH1 protein, Arabidopsis; C512593:PKS4 protein, Arabidopsis; D017346:Protein Serine-Threonine Kinases; C552692:WAG1 protein, Arabidopsis; C542125:WAG2 protein, Arabidopsis