Abstract

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 only the AtDRTS2 promoter can drive a strong proliferation-specific expression in both root and shoot apical meristems. In contrast, AtDRTS1 is highly expressed in vascular tissues but not in the meristems, whereas AtDRTS3 showed strong expression in the shoot meristem but not in the meristems of the roots, where its activity was confined to the columella and the central cylinder. The AtDRTS2 and AtDRTS3 promoters contain E2F binding sites which, according to ChIP analyses, are recognized in vivo by E2F factors. Functional analyses performed in transgenic plants have revealed a repressive role of these sites in the control of the expression of both AtDRTS2 and AtDRTS3. Additional cis-acting elements have been identified in the AtDRTS2 promoter and appear to up-regulate its meristematic expression. Moreover, expression of the AtDRTS2 gene depends on the presence of a small region of the first intron which shows no similarity to other known plant cis-elements.

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