Gene regulation during late embryogenesis: the RY motif of maturation-specific gene promoters is a direct target of the FUS3 gene product

The Arabidopsis mutants fus3 and abi3 show pleiotropic effects during embry ogenesis including reduced levels of transcripts encoding embryo-specific s eed proteins. To investigate the interaction between the BO-domain-containi ng transcription factors FUSS and ABI3 with the RY cis-motif, conserved in many seed-specific promoters, a promoter analysis as well as band-shift exp eriments were performed. The analysis of promoter mutants revealed the stru ctural requirements for the function of the RY cis-element. It is shown tha t both the nucleotide sequence and the alternation of purin and pyrimidin n ucleotides (RY character) are essential for the activity of the motif. Furt her, it was shown that FUSS and ABI3 can act independently of each other in controlling promoter activity and that the RY cis-motif is a target for bo th transcription factors. For FUSS, which is so far the smallest known memb er of the B3-domain family, a physical interaction with the RY motif was es tablished. The functional and biochemical data demonstrate that the regulat ors FUSS and ABI3 are essential components of a regulatory network acting i n concert through the RY-promoter element to control gene expression during late embryogenesis and seed development.