MORE THAN 80R2R3-MYB REGULATORY GENES IN THE GENOME OF ARABIDOPSIS-THALIANA

Transcription factors belonging to the R2R3-MYB family contain the rel ated helix-turn-helix repeats R2 and R3. The authors isolated partial cDNA and/or genomic clones of 78 R2R3-MYB genes from Arabidopsis thali ana and found accessions corresponding to 31 Arabidopsis genes of this class in databanks, seven of which were not represented in the author s' collection. Therefore, there are at least 85, and probably more tha n 100, R2R3-MYB genes present in the Arabidopsis thaliana genome, repr esenting the largest regulatory gene family currently known in plants. In contrast, no more than three R2R3-MYB genes have been reported in any organism from other phyla. DNA-binding studies showed that there a re differences but also frequent overlaps in binding specificity among plant R2R3-MYB proteins, in line with the distinct but often related functions that are beginning to be recognized for these proteins. This large-sized gene family may contribute to the regulatory flexibility underlying the developmental and metabolic plasticity displayed by pla nts.