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JXB Advance Access published online on July 4, 2008
Journal of Experimental Botany, doi:10.1093/jxb/ern170
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© The Author [2008]. Published by Oxford University Press [on behalf of the Society for Experimental Biology]. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

RESEARCH PAPER

The sunflower HD-Zip transcription factor HAHB4 is up-regulated in darkness, reducing the transcription of photosynthesis-related genes

Pablo A. Manavella1, Carlos A. Dezar1, Federico D. Ariel1, María F. Drincovich2 and Raquel L. Chan1,*

1Cátedra de Biología Celular y Molecular, Facultad de Bioquímica y Ciencias Biológicas, Universidad Nacional del Litoral, CONICET, CC 242 Ciudad Universitaria, 3000, Santa Fe, Argentina
2Centro de Estudios Fotosintéticos y Bioquímicos (CEFOBI), Universidad Nacional de Rosario, CONICET, Suipacha 531, 2000, Rosario, Argentina

* To whom correspondence should be addresssed. E-mail: rchan{at}fbcb.unl.edu.ar

HAHB4 belongs to the sunflower subfamily I of HD-Zip proteins and is involved in drought-tolerance response and ethylene-mediated senescence. Cross-talk between these two processes through this transcription factor was recently described. In this study it is shown that the expression of HAHB4 is induced in darkness and quickly disappears when plants are exposed to light. This regulation of HAHB4 was confirmed at the transcriptional level through the use of transgenic Arabidopsis plants bearing constructs in which different segments of the HAHB4 promoter were fused with the reporter gene GUS. Together with electrophoretic mobility shift assays performed with sunflower nuclear proteins, these experiments allowed a cis-acting element involved in this response to be located. Transient overexpression of the HAHB4 cDNA in sunflower leaf discs and HAHB4 knockdown by iRNA were performed, demonstrating the participation of this transcription factor in the transcriptional down-regulation of a large group of photosynthesis-related genes. In accordance with the reduction in the transcripts encoding chlorophyll a/b-binding proteins, the content of these pigments is diminished in Arabidopsis HAHB4-expressing transgenic plants. Thus, it appears that HAHB4 may participate with other factors in the intricate regulation mechanism of the photosynthetic machinery in darkness.

Key words: Dark-inducible promoter, dark regulation, HAHB4, HD-Zip, promoter analysis, sunflower, transcription factor

Received 18 March 2008; Revised 19 May 2008 Accepted 22 May 2008


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