Conserved noncoding sequences (CNSs) in DNA are reliable pointers to regulatory 
elements controlling gene expression. Using a comparative genomics approach with 
four dicotyledonous plant species (Arabidopsis thaliana, papaya [Carica papaya], 
poplar [Populus trichocarpa], and grape [Vitis vinifera]), we detected hundreds 
of CNSs upstream of Arabidopsis genes. Distinct positioning, length, and 
enrichment for transcription factor binding sites suggest these CNSs play a 
functional role in transcriptional regulation. The enrichment of transcription 
factors within the set of genes associated with CNS is consistent with the 
hypothesis that together they form part of a conserved transcriptional network 
whose function is to regulate other transcription factors and control 
development. We identified a set of promoters where regulatory mechanisms are 
likely to be shared between the model organism Arabidopsis and other dicots, 
providing areas of focus for further research.