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Plant and Cell Physiology Advance Access published online on October 8, 2005
Plant and Cell Physiology, doi:10.1093/pcp/pci210
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Plant and Cell Physiology 2005 © The Japanese Society of Plant Physiologists (JSPP); all rights reserved.
Received April 7, 2005
Accepted September 28, 2005

Regular Paper

Hahb-10, a Sunflower Homeobox-Leucine Zipper Gene, Is Regulated by Light Quality and Quantity and Promotes Early Flowering when Expressed in Arabidopsis

Eva C. Rueda 1, Carlos A. Dezar 1, Daniel H. Gonzalez 1, and Raquel L. Chan 1*

1 Cátedra de Biología Celular y Molecular, Facultad de Bioquímica y Ciencias Biológicas, Universidad Nacional del Litoral, CC 242 Paraje El Pozo, 3000 Santa Fe, Argentina

* To whom correspondence should be addressed.
Raquel L. Chan, E-mail: rchan{at}fbcb.unl.edu.ar


  Abstract

Homeodomain-leucine zipper proteins constitute a family of transcription factors found only in plants. Expression patterns of the sunflower homeobox-leucine zipper gene Hahb-10 (Helianthus annuus homeobox-10), that belongs to the HD-Zip II subfamily, were analysed. Northern blots showed that Hahb-10 is expressed primarily in mature leaves, although expression is clearly detectable in younger leaves and also in stems. Considerably higher expression levels were detected in etiolated seedlings respective to light-grown seedlings. Induction of Hahb-10 expression was observed when seedlings were subjected to a treatment with gibberellins. Transgenic Arabidopsis thaliana plants that express Hahb-10 under the 35S cauliflower mosaic virus promoter show special phenotypic characteristics like darker cotyledons and planar leaves. A reduction in the life cycle of about 25% allowing earlier seed collection was also observed, an this phenomenon is clearly related to a shortened flowering time. When the number of plants per pot increased, the difference in developmental rate between transgenic and non-transformed individuals became larger. After gibberellin treatment, the relative difference in life cycle duration was considerably reduced. Several light-regulated genes have been tested as possible target genes of Hahb-10. One of them, PsbS, shows a different response to illumination conditions in transgenic plants compared with the response in wild-type ones while the other genes behave similarly in both genotypes. We propose that Hahb-10 functions in signalling cascade(s) that control(s) plant responses to light quality and quantity, and may also be involved in gibberellin transduction pathways.

Keywords: HD-Zip; homeodomain; Hahb-10; light regulated expression; gibberellin; sunflower homeodomain-leucine zipper; PsbS.
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P. A. Manavella, C. A. Dezar, F. D. Ariel, M. F. Drincovich, and R. L. Chan
The sunflower HD-Zip transcription factor HAHB4 is up-regulated in darkness, reducing the transcription of photosynthesis-related genes
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