title: Different mechanisms participate in the R-dependent activity of the R2R3 MYB transcription factor C1.
abstract: The R2R3 MYB transcription factor C1 requires the basic helix-loop-helix factor R as an essential co-activator for the transcription of maize anthocyanin genes. In contrast, the R2R3 MYB protein P1 activates a subset of the C1-regulated genes independently of R. Substitution of six amino acids in P1 with the C1 amino acids results in P1(*), whose activity on C1-regulated and P1-regulated genes is R-dependent or R-enhanced, respectively. We have used P1(*) in combination with various promoters to uncover two mechanisms for R function. On synthetic promoters that contain only C1/P1 binding sites, R is an essential co-activator of C1. This function of R is unlikely to simply be the result of an increase in the C1 DNA-binding affinity, since transcriptional activity of a C1 mutant that binds DNA at a higher affinity, comparable with P1, remains R-dependent. The differential transcriptional activity of C1 fusions with the yeast Gal4 DNA-binding domain in yeast and maize cells suggests that part of the function of R is to relieve C1 from a plant-specific inhibitor. A second function of R requires cis-regulatory elements in addition to the C1/P1 DNA-binding sites for R-enhanced transcription of a1. We hypothesize that R functions in this mode by binding or recruiting additional factors to the anthocyanin regulatory element conserved in the promoters of several anthocyanin genes. Together, these findings suggest a model in which combinatorial interactions with co-activators enable R2R3 MYB factors with very similar DNA binding preferences to discriminate between target genes in vivo.
authors.affiliation: Ohio State Biochemistry Program, Department of Plant Cellular and Molecular Biology, and Plant Biotechnology Center, The Ohio State University, Columbus, Ohio 43210, USA.
authors.forename: J Marcela
authors.initials: JM
authors.lastname: Hernandez
authors.forename: George F
authors.initials: GF
authors.lastname: Heine
authors.forename: Niloufer G
authors.initials: NG
authors.lastname: Irani
authors.forename: Antje
authors.initials: A
authors.lastname: Feller
authors.forename: Min-Gab
authors.initials: MG
authors.lastname: Kim
authors.forename: Todd
authors.initials: T
authors.lastname: Matulnik
authors.forename: Vicki L
authors.initials: VL
authors.lastname: Chandler
authors.forename: Erich
authors.initials: E
authors.lastname: Grotewold
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D005419:Flavonoids / Q000096:biosynthesis; D018506:Gene Expression Regulation, Plant; D018257:Helix-Loop-Helix Motifs; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D020798:Two-Hybrid System Techniques
chemical_list: D029681:Arabidopsis Proteins; C482738:BOTRYTIS SUSCEPTIBLE1 protein, Arabidopsis; D004268:DNA-Binding Proteins; D005419:Flavonoids; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors