ABSTRACT

Transcription factors are classified on the basis of conserved DNA binding motifs. In vertebrates, MYB proteins are defined by the presence of a specific DNA- binding domain, consisting of three imperfect repeats (Rl, R2, R3) of about 52 residues, each one folding into a helix-turn-helix motif. These proteins constitute a small gene family, whose members are involved in the control of cell cycle progression. In plants, MYB proteins generally contain the R2 and R3 repeats, but single- and three-repeat MYB transcription factors have also been found. The plant MYB genes functionally characterized so far suggest the crucial involvement of this large family in many different plant-specific processes. More than 100 MYB genes distributed throughout the Arabidopsis genome have been described, but only a few of them has an assigned function. Some are known to control trichome cell specification, root hair differentiation and tryptophan biosynthesis, some others are involved in the response of plants to environmental stimuli and play a role in the circadian clock. Preliminary expression studies on more than 80 members of the Arabidopsis MYB family indicated that most MYB genes show distinct but overlapping functions, indicating the potential of MYB genes to contribute to the regulation of a wide range of physiological processes.