The sunflower HD-Zip transcription factor HAHB4 is up regulated in darkness acting as a repressor of photosynthesis related genes transcription.

MANAVELLA PABLO ANDRÉS; DEZAR CARLOS ALBERTO; ARIEL FEDERICO DAMIÁN; DRINCOVICH MARÍA FABIANA; CHAN RAQUEL LÍA

JOURNAL OF EXPERIMENTAL BOTANY

OXFORD UNIV PRESS

Año: 2008 vol. 59 p. 3143 - 3155

0022-0957

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. Herein, 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 (EMSAs) performed with sunflower nuclear proteins, these experiments allowed us to locate a cis-acting element involved in this response. Transient overexpression of the HAHB4 cDNA in sunflower leaf disks and HAHB4 knockdown by iRNA were performed, demonstrating the participation of this transcription factor in the transcriptional downregulation 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.