ECTOPIC EXPRESSION OF A NOVEL MYB GENE MODIFIES THE ARCHITECTURE OF THE ARABIDOPSIS INFLORESCENCE

The Arabidopsis thaliana mutants fus3 lec1 and abi3 have pleiotropic d efects during late embryogenesis. Mutant embryos fail to enter the mat uration programme and initiate a vegetative germination pathway instea d. Screening for genes which are differentially expressed in the fus3 mutant of Arabidopsis resulted in the isolation of several members of the MYB family. MYB domain proteins in plants represent an extended ge ne family of transcription factors, suggesting their participation in a variety of plant specific cellular functions. Here, the authors desc ribe one of these genes, designated AtMYB13, representing a novel memb er of the MYB gene family. The structure of the gene as well as its ge nomic organisation and localisation are reported. The expression of th e gene is regulated by dehydration, exogenous abscisic acid, light and wounding. A chimeric AtMYB13 promoter/GUS gene is tissue-specifically expressed in transgenic Arabidopsis plants. The GUS staining was pred ominantly detected in the shoot apex zone and at the basis of developi ng flowers. In addition, the AtMYB13 gene promoter is active at branch ing points of the inflorescence. Furthermore, ectopic expression of th e AtMYB13 gene has a characteristic impact on the architecture of the inflorescence leading to peculiar hook structures at pedicel branching points. In addition, some transgenic plants exhibit a reversed order of first flowers and axillary buds. These data suggest a function of t he AtMYB13 gene product in linking shoot morphogenic activity with env ironmental as well as intrinsic signals.