Functional characterization of a stress-inducible/organ-specific sunflower transcription factor promoter

PABLO MANAVELLA; CARLOS DEZAR; RAQUEL CHAN

Rosario-Santa Fe

Simposio; Simposio de Biotecnología DAAD; 2005

DAAD

  Homeodomain-leucine zipper proteins (HD-Zip), unique to plants, are transcription factors with a characteristic feature, they have an homeodomain associated to a leucine zipper in their structure. This protein family can be divided in four subfamilies according to sequence homology in and outside the conserved domains. These transcription factors bind DNA as dimers and their function in plants is related to developmental processes associated to environmental changes. Hahb-4 is a previously described member of the sunflower HD-Zip subfamily I. This gene expression is regulated by water stress at the transcriptional level. Arabidopsis transgenic plants that overexpress the cDNA under the control of a constitutive promoter show an enhanced tolerance to drought as well as a characteristic morphological phenotype. We have isolated and analysed the promoter region of this sunflower nuclear gene.  This region is represented in two different but highly conserved alleles of 1015 and 1221 bp, respectively, in the sunflower hybrid studied. To gain insight into the structure and function of these promoter forms, we have obtained plants stably transformed with different fragments fused to the b-glucuronidase (gus) reporter gene and analyzed them by histochemical staining, fluorometry and northern blots as well as by real-time RT-PCR. We present results that demonstrate that Hahb-4 expression is transcriptionally regulated by illumination conditions. Site directed mutagenesis and chimeric constructions were done in order to identify the sequences responsible for each specific response. Combination of the three methodologies allow us to determine the location of minimal segments of DNA, neccessary for root specific expression, water stress induction and regulation by light/dark. The observations done open the posibility of biotechnological uses of these DNA segments as tools to direct expression of this or others genes in transgenic plants.