Universität zu Köln

The aim of the work presented here was the isolation of genes which control the transition from vegetative to reproductive growth in higher plants.The molecular mechanisms underlying this developmental phase change, known as the floral transition, are still poorly understood. Because activation of the floral meristem identity gene FLORICAULA (FLO) from Antirrhinum majus (Snapdragon) demarcates the end of the floral transition, its transcriptional regulators are good candidates to represent such controlling genes. As a strategy to identify possible regulators of FLO, gel retardation experiments were performed. Possible cis-acting elements were identified in an AT-rich region (-213/-94) upstream of the translation start-codon of the FLO gene. Subsequent south-western-screening of an A. majus inflorescence cDNA expression library using the corresponding DNA-fragment resulted in the identification of two cDNAs, HMR1 and SAP1, both encoding AT-hook DNA-binding proteins. Screening the electronic databases revealed HMR1 to be a member of the HMG-Y-like DNA-binding protein family. Besides its family-typic features, HMR1 contains two leucine-zipper motifs. SAP1, however, likely represents a novel DNA-binding protein family found in all higher plants. Additional gel retardation experiments suggest that SAP1 binds its target-DNA in a cooperative manner, probably mediated by a novel protein domain. Although a role of HMR1 and SAP1 in the floral transition cannot be excluded, their expression pattern does not suggest a function limited to this developmental process. A preliminary analysis of HMR1 antisense transgenic plants suggests an involvement of HMR1 in the regulation of class B-genes and internode elongation.

English