In Barley, the dominant Hooded (K) phenotype is associated with the duplication of a 305 bp element in intron IV of the knox gene BKn3. This regulatory element seems to act as an enhancer and causes ectopic expression of Bkn3 in the lemma-awn transition zone, leading to the formation of a new meristem that develops into an epiphyillic flower. A one hybrid screening aimed at isolating putative regulators of the BKn3 gene uncovered four different proteins capable of interacting with the 305 bp element (K Intron Binding Proteins, KIBPs). In order to gain insight into their role in BKn3 regulation, recombinant KIBPs have been expressed in different prokaryotic systems and the full length proteins have been purified by affinity chromatography. In vitro binding of KIBPs to the 305 bp enhancer has been confirmed by "Electro Mobility Shift Assay" (EMSA) and the minimal binding sites have been assessed. As there is no clear association between KIBP loci and mutations already mapped and characterised in barley, the in vivo function of KIBPs has been investigated in the model species Oryza sativa. Screening of insertional mutant collections has yielded stable lines carrying mutations in two KIBP-related genes: in the first line, a Ds insertion causes defects in tillering and internode elongation, while in the second line, a T -DNA insertion is responsible for lethality in 4 weeks-old seedlings. In addition, morphogenetic effects of KIBPs overexpression in transgenic rice plants are under investigation. (Texte intégral)