TOWARDS FUNCTIONAL-CHARACTERIZATION OF THE MEMBERS OF THE R2R3-MYB GENE FAMILY FROM ARABIDOPSIS-THALIANA

Transcription factors containing a conserved DNA-binding domain simila r to that of the proto-oncogene c-myb have been identified in nearly a ll eukaryotes. MYB-related proteins from plants generally contain two related helix-turn-helix motifs, the R2 and R3 repeats. It was estimat ed that Arabidopsis thaliana contains more than 100 R2R3-MYB genes. Th e few cases where functional data are available suggest an important r ole of these genes in the regulation of secondary metabolism, the cont rol of cell shape, disease resistance, and hormone responses. To deter mine the full regulatory potential of this large family of regulatory genes, a systematic search for the function of all genes of this famil y was initiated. Sequence data for more than 90 different A. thaliana R2R3-MYB genes have been obtained. Sequence comparison revealed conser ved amino acid motifs shared by subgroups of R2R3-MYB genes in additio n to the characteristic DNA-binding domain. No significant clustering of the genes was detected, although they are not uniformly distributed throughout the A. thaliana genome. R2R3-MYB gene expression levers we re determined under more than 20 different growth conditions including hormone treatment, infection with pathogens and various stress condit ions. MYB genes are specifically expressed in different tissues and ph ysiological conditions, indicating the potential for involvement in va rious regulatory processes. The sequence and expression data together with the map positions of nearly all MYB genes in A. thaliana provide a substantial basis for further studies of this important group of tra nscription factors.