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1.  Cryptochrome 1 and phytochrome B control shade-avoidance responses in Arabidopsis via partially-independent hormonal cascades 
Summary
Plants respond to a reduction in the red:far-red ratio (R:FR) of light caused by the proximity of other plants by initiating morphological changes that improve light capture. In Arabidopsis, this response (the shade avoidance syndrome, SAS) is controlled by the phytochromes (particularly phyB) and dependent on the TAA1 pathway of auxin biosynthesis. However, when grown in real canopies, we found that phyB mutants and mutants deficient in TAAI (sav3) still display robust SAS responses to increased planting density and leaf shading. The SAS morphology (leaf hyponasty and reduced lamina:petiole ratio) could be phenocopied by exposing plants to blue (B) light attenuation. These responses to B light attenuation required the UV-A/blue light photoreceptor cry1. Moreover, they were mediated through mechanisms that showed only limited overlap with the pathways recruited by phyB inactivation. In particular, pathways for polar auxin transport, auxin biosynthesis and gibberellin signaling that are involved in SAS responses to low R:FR were not required for the SAS responses to B light depletion. By contrast, brassinosteroid response appeared to be required for full expression of the SAS phenotype under low B light. The phyB and cry1 inactivation pathways appeared to converge in their requirement for the bHLH transcription factors PHYTOCHROME INTERACTING FACTOR 4 and 5 (PIF4 and 5) to elicit the SAS phenotype. Our results suggest that B light is an important control of SAS responses, and that PIF4 and PIF5 are critical hubs for a diverse array of signaling routes that control plant architecture in canopies.
doi:10.1111/j.1365-313X.2011.04598.x
PMCID: PMC3135679  PMID: 21457375
Blue light; Brassinosteroid; Phytochrome Interacting Factors (PIFs); PIN3; TAA1; DELLA
2.  Phototropism: Mechanism and Outcomes 
Plants have evolved a wide variety of responses that allow them to adapt to the variable environmental conditions in which they find themselves growing. One such response is the phototropic response - the bending of a plant organ toward (stems and leaves) or away from (roots) a directional blue light source. Phototropism is one of several photoresponses of plants that afford mechanisms to alter their growth and development to changes in light intensity, quality and direction. Over recent decades much has been learned about the genetic, molecular and cell biological components involved in sensing and responding to phototropic stimuli. Many of these advances have been made through the utilization of Arabidopsis as a model for phototropic studies. Here we discuss such advances, as well as studies in other plant species where appropriate to the discussion of work in Arabidopsis.
doi:10.1199/tab.0125
PMCID: PMC3244944  PMID: 22303252
3.  Cryptochrome 1 and phytochrome B control shade-avoidance responses in Arabidopsis via partially independent hormonal cascades 
The Plant Journal  2011;67(2):195-207.
Plants respond to a reduction in the red/far-red ratio (R:FR) of light, caused by the proximity of other plants, by initiating morphological changes that improve light capture. In Arabidopsis, this response (shade avoidance syndrome, SAS) is controlled by phytochromes (particularly phyB), and is dependent on the TAA1 pathway of auxin biosynthesis. However, when grown in real canopies, we found that phyB mutants and mutants deficient in TAAI (sav3) still display robust SAS responses to increased planting density and leaf shading. The SAS morphology (leaf hyponasty and reduced lamina/petiole ratio) could be phenocopied by exposing plants to blue light attenuation. These responses to blue light attenuation required the UV-A/blue light photoreceptor cry1. Moreover, they were mediated through mechanisms that showed only limited overlap with the pathways recruited by phyB inactivation. In particular, pathways for polar auxin transport, auxin biosynthesis and gibberellin signaling that are involved in SAS responses to low R:FR were not required for the SAS responses to blue light depletion. By contrast, the brassinosteroid response appeared to be required for the full expression of the SAS phenotype under low blue light. The phyB and cry1 inactivation pathways appeared to converge in their requirement for the basic/helix-loop-helix (bHLH) transcription factors PHYTOCHROME INTERACTING FACTORs 4 and 5 (PIF4 and PIF5) to elicit the SAS phenotype. Our results suggest that blue light is an important control of SAS responses, and that PIF4 and PIF5 are critical hubs for a diverse array of signaling routes that control plant architecture in canopies.
doi:10.1111/j.1365-313X.2011.04598.x
PMCID: PMC3135679  PMID: 21457375
blue light; brassinosteroid; phytochrome interacting factors (PIFs); PIN3; Tryptophan Aminotransferase of Arabidopsis 1; DELLA

Results 1-3 (3)