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

MANAVELLA, P ; DEZAR, CA; ARIEL, FD; DRINCOVICH, M; CHAN, RL

JOURNAL OF EXPERIMENTAL BOTANY

Oxford Journals

Lugar: Oxford; Año: 2008 vol. 59 p. 3143 - 3155

1460-2431

HAHB4 belongs to the sunflower subfamily I of HD-Zipproteins and is involved in drought-tolerance responseand ethylene-mediated senescence. Cross-talk betweenthese two processes through this transcriptionfactor was recently described. In this study it is shownthat the expression of HAHB4 is induced in darknessand quickly disappears when plants are exposed tolight. This regulation of HAHB4 was confirmed at thetranscriptional level through the use of transgenicArabidopsis plants bearing constructs in which differentsegments of the HAHB4 promoter were fused withthe reporter gene GUS. Together with electrophoreticmobility shift assays performed with sunflower nuclearproteins, these experiments allowed a cis-acting elementinvolved in this response to be located. Transientoverexpression of the HAHB4 cDNA in sunflower leafdiscs and HAHB4 knockdown by iRNA were performed,demonstrating the participation of this transcriptionfactor in the transcriptional down-regulationof a large group of photosynthesis-related genes. Inaccordance with the reduction in the transcriptsencoding chlorophyll a/b-binding proteins, the contentof these pigments is diminished in ArabidopsisHAHB4-expressing transgenic plants. Thus, it appearsthat HAHB4 may participate with other factors in theintricate regulation mechanism of the photosyntheticmachinery in darkness.Key words: Dark-inducible