Arabidopsis thaliana contains three dhfr/ts (dihydrofolate reductase/thymidylate synthase) genes showing divergent patterns of expression. Analyses of promoter activity in transgenic plants have revealed that AtDRTS1 is highly expressed in vascular tissues but not in the meristems, whereas the AtDRTS2 promoter drives a strong proliferation-specific expression in both root and shoot apical meristems. In contrast, AtDRTS3 showed strong expression in root columella and central cylinder, as well as in parts of the shoot meristem but not in root meristems. E2F binding sites, which are often involved in cell cycle-dependent expression, are contained in the AtDRTS2 and AtDRTS3 promoters. ChIP analyses have revealed that these sites are recognized in vivo by E2F factors. Functional analyses performed in transgenic plants have confirmed an important role of these sites in the control of the expression of both AtDRTS2 and AtDRTS3. Additional cis-acting elements regulating the meristematic expression of AtDRTS2 will also be described.
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