Abstract
BackgroundThe maize INDETERMINATE1 gene, ID1, is a key regulator of the transition to flowering and the founding member of a transcription factor gene family that encodes a protein with a distinct arrangement of zinc finger motifs. The zinc fingers and surrounding sequence make up the signature ID domain (IDD), which appears to be found in all higher plant genomes. The presence of zinc finger domains and previous biochemical studies showing that ID1 binds to DNA suggests that members of this gene family are involved in transcriptional regulation.ResultsComparison of IDD genes identified in Arabidopsis and rice genomes, and all IDD genes discovered in maize EST and genomic databases, suggest that ID1 is a unique member of this gene family. High levels of sequence similarity amongst all IDD genes from maize, rice and Arabidopsis suggest that they are derived from a common ancestor. Several unique features of ID1 suggest that it is a divergent member of the maize IDD family. Although no clear ID1 ortholog was identified in the Arabidopsis genome, highly similar genes that encode proteins with identity extending beyond the ID domain were isolated from rice and sorghum. Phylogenetic comparisons show that these putative orthologs, along with maize ID1, form a group separate from other IDD genes. In contrast to ID1 mRNA, which is detected exclusively in immature leaves, several maize IDD genes showed a broad range of expression in various tissues. Further, Western analysis with an antibody that cross-reacts with ID1 protein and potential orthologs from rice and sorghum shows that all three proteins are detected in immature leaves only.ConclusionComparative genomic analysis shows that the IDD zinc finger family is highly conserved among both monocots and dicots. The leaf-specific ID1 expression pattern distinguishes it from other maize IDD genes examined. A similar leaf-specific localization pattern was observed for the putative ID1 protein orthologs from rice and sorghum. These similarities between ID1 and closely related genes in other grasses point to possible similarities in function.
Highlights
The maize INDETERMINATE1 gene, ID1, is a key regulator of the transition to flowering and the founding member of a transcription factor gene family that encodes a protein with a distinct arrangement of zinc finger motifs
In initial attempts to isolate the ID1 coding sequence, cDNA libraries made from 3-leaf seedling, vegetative apex, and developing inflorescence were screened with a portion of the ID1 genomic sequence
More than hybridizing clones were isolated from these libraries and found to correspond to 4 different classes of cDNAs that were similar to ID1, none of them corresponded to the maize ID1 gene
Summary
The maize INDETERMINATE1 gene, ID1, is a key regulator of the transition to flowering and the founding member of a transcription factor gene family that encodes a protein with a distinct arrangement of zinc finger motifs. The presence of zinc finger domains and previous biochemical studies showing that ID1 binds to DNA suggests that members of this gene family are involved in transcriptional regulation. The transition to flowering is mediated by a complex network of pathways that integrate both environmental and developmental signals [8] so it is not surprising that some gene functions are conserved, whereas other genes appear to have evolved distinctive functions to meet the specific floral transition requirements within a particular species
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