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  • The EMBO Journal (2007) 26, 4756 - 4767
  • doi:10.1038/sj.emboj.7601890

Published online: 18 October 2007

Interaction of shade avoidance and auxin responses: a role for two novel atypical bHLH proteins

Irma Roig-Villanova1,a, Jordi Bou-Torrent1,a, Anahit Galstyan1, Lorenzo Carretero-Paulet1,b, Sergi Portolés1, Manuel Rodríguez-Concepción1,2 and Jaime F Martínez-García1,3

  1. Laboratori de Genètica Molecular Vegetal Consorci CSIC-IRTA, Departament de Genètica Molecular, Barcelona, Spain
  2. Departament de Bioquímica i Biologia Molecular, Universitat de Barcelona, Barcelona, Spain
  3. Institució Catalana de Recerca i Estudis Avançats, Barcelona, Spain

Correspondence to:

Jaime F Martínez-García, Laboratori de Genètica Molecular Vegetal, Consorci CSIC-IRTA, Departament de Genètica Molecular, c. Jordi Girona 18-26, Barcelona 8034, Spain. Tel.: +34 93 400 6189; Fax: +34 93 402 5904; E-mail: jmggmg@ibmb.csic.es

aThese authors contributed equally to this work

bPresent address: Departamento de Biología Aplicada, Universidad de Almería, Ctra. Sacramento s/n, La Cañada de San Urbano, Almería 04120, Spain

Received 14 March 2007; Accepted 24 September 2007

Plants sense the presence of potentially competing nearby individuals as a reduction in the red to far-red ratio of the incoming light. In anticipation of eventual shading, a set of plant responses known as the shade avoidance syndrome (SAS) is initiated soon after detection of this signal by the phytochrome photoreceptors. Here we analyze the function of PHYTOCHROME RAPIDLYREGULATED1 (PAR1) and PAR2, two Arabidopsis thaliana genes rapidly upregulated after simulated shade perception. These genes encode two closely related atypical basic helix–loop–helix proteins with no previously assigned function in plant development. Using reverse genetic approaches, we show that PAR1 and PAR2 act in the nucleus to broadly control plant development, acting as negative regulators of a variety of SAS responses, including seedling elongation and photosynthetic pigment accumulation. Molecularly, PAR1 and PAR2 act as direct transcriptional repressors of two auxin-responsive genes, SMALLAUXINUPREGULATED15 (SAUR15) and SAUR68. Additional results support that PAR1 and PAR2 function in integrating shade and hormone transcriptional networks, rapidly connecting phytochrome-sensed light changes with auxin responsiveness.

  • Keywords:

    • Arabidopsis,
    • auxin,
    • phytochrome,
    • SAUR,
    • shade avoidance