The regulator of MAT2 (ROM2) protein binds to early maturation promoters and represses PvALF-activated transcription.
The regulation of maturation (MAT)- and late embryogenesis (LEA)-specific gene expression in dicots involves factors related to ABI3, a seed-specific component of the abscisic acid signal transduction pathways from Arabidopsis. In French bean (Phaseolus vulgaris), the ABI3-like factor, PvALF, activates transcription from MAT promoters of phytohemagglutinin (DLEC2) and beta-phaseolin (PHS beta) genes. We describe the regulator of MAT2 (ROM2) as a basic leucine zipper (bZIP) DNA binding protein that recognizes motifs with symmetric (ACGT) and asymmetric (ACCT) core elements present in both MAT promoters. ROM2 antagonizes trans-activation of the DLEC2 promoter by PvALF in transient expression assays. Repression was abolished by mutations that prevented binding of ROM2 to the DLEC2 seed enhancer region. Moreover, a hybrid protein composed of a PvALF activation domain and the DNA binding and dimerization domain of ROM2 activated gene expression, indicating that ROM2 recognizes the DLEC2 enhancer in vivo; consequently, ROM2 functions as a DNA binding site-dependent repressor. Supershift analysis of nuclear proteins, using a ROM2-specific antibody, revealed an increase in ROM2 DNA binding activity during seed desiccation. A corresponding increase in ROM2 mRNA coincided with the period when DLEC2 mRNA levels declined in embryos. These results demonstrate developmental regulation of the ROM2 repressor and point to a role for this factor in silencing DLEC2 transcription during late embryogenesis.
Chern
M S
MS
Department of Biological Sciences, University of Maryland-Baltimore County 21228-5398, USA.
Bobb
A J
AJ
Bustos
M M
MM
D000040:Abscisic Acid / Q000502:physiology; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000502:physiology*; D001483:Base Sequence; D050976:Basic-Leucine Zipper Transcription Factors; D003001:Cloning, Molecular; D017931:DNA Primers; D018076:DNA, Complementary; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli; D007887:Fabaceae / Q000235:genetics / Q000502:physiology*; D018506:Gene Expression Regulation, Plant; D016350:Leucine Zippers; D008969:Molecular Sequence Data; D015345:Oligonucleotide Probes; D010940:Plant Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D010946:Plants, Medicinal; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism*; D014158:Transcription, Genetic
D050976:Basic-Leucine Zipper Transcription Factors; D017931:DNA Primers; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D015345:Oligonucleotide Probes; D010940:Plant Proteins; C096083:PvAlf protein, Phaseolus vulgaris; C099056:ROM2 protein, Phaseolus vulgaris; D011994:Recombinant Proteins; D015534:Trans-Activators; D000040:Abscisic Acid