Different mechanisms participate in the R-dependent activity of the R2R3 MYB transcription factor C1.
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.
Hernandez
J Marcela
JM
Ohio State Biochemistry Program, Department of Plant Cellular and Molecular Biology, and Plant Biotechnology Center, The Ohio State University, Columbus, Ohio 43210, USA.
Heine
George F
GF
Irani
Niloufer G
NG
Feller
Antje
A
Kim
Min-Gab
MG
Matulnik
Todd
T
Chandler
Vicki L
VL
Grotewold
Erich
E
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
D029681:Arabidopsis Proteins; C482738:BOTRYTIS SUSCEPTIBLE1 protein, Arabidopsis; D004268:DNA-Binding Proteins; D005419:Flavonoids; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors