Isolation and molecular analysis of two R2R3-MYB genes from the sunflower (Helianthus annuus)

Abstract

MYB factors comprise one of the largest family of transcription factors (TFs) characterized by a highly conserved DNA-binding domain: the MYB domain. From the sunflower (Helianthus annuus L.) genome, we have isolated two R2R3-type MYB TFs (Ha-R2R3-MYB1 and Ha-R2R3-MYB2) that show homology with the functional domain of most R2R3-MYB proteins of other species. The R2 (53 amino acids) and R3 (51 amino acids) motifs of the sunflower MYB TFs contain typical amino acids, including a series of highly conserved tryptophan residues, which play a key role in sequence-specific DNA binding. In the MYB domain, both genes (Ha-R2R3-MYB1 and Ha-R2R3-MYB2) exhibit the highly conserved splicing arrangement of three exons and two introns. Using in situ hybridization, a weak level of Ha-R2R3-MYB1 transcription was uniformly spread in shoot apical meristem (SAM), as well as in axillary meristem (AM). By contrast, Ha-R2R3-MYB2 transcription was strongly restricted to a small domain within the boundary zone separating the SAM and the leaf primordia, suggesting that Ha-R2R3-MYB2 may be involved in an early step of AM development.