THE BIOGENESIS OF THE PHOTOSYNTHETIC APPARATUS IS REPPRESED BY THE TRANSCRIPTION FACTOR HAHB-4

PABLO MANAVELLA; CARLOS DEZAR; RAQUEL CHAN

Rosario

Congreso; XLII Reunión Anual de SAIB; 2006

SAIB

Expression of the sunflower Hahb-4 transcription factor (TF) is regulated by ethylene, drought and ABA as previously reported. Here we show that the expression of this TF is strongly induced also in dark. Such light-dependent regulation was only observed on photosynthetic tissues. In order to locate the promoter cis-acting elements responsible for this regulation we obtained constructs (deletions, chimeras) of the Hahb-4 promoter controlling the reporter gus activity. Analysis of transgenic plants bearing these constructs allowed us to locate sequences involved in the response to dark between positions -319 and ?419. Using site directed mutagenesis we found out a GT-1 binding site in the promoter responsible for its response to dark. Aiming to elucidate the significance of these observations we performed a microarray experiment of Hahb-4 overexpressing plants. The analysis of the obtained data revealed that a large number of genes involved in the photosynthetic machinery biogenesis is repressed. The results, together with transpiration rates and CO2 fixation measurements, suggest that Hahb-4 functions unleashing a mechanism able to turn off the photosynthetic machinery. We conclude that Hahb-4, also up regulated during hydric stress, can reduce the photo-oxidative stress produced by photosynthesis during periods of drought and consequently contributes to the observed drought tolerance.