SummaryWe have focused our interest on two cis-regulatory elements, named site II motif and telo box, identi®ed within the promoter of plant proliferating cellular nuclear antigen (PCNA) and putatively involved in meristematic expression of the gene. A conserved topological association between site II motifs and telo boxes is observed in the promoter of numerous genes expressed in cycling cells, including several cell cyclerelated genes and 153 Arabidopsis genes encoding ribosomal proteins. Meristematic expression of a GUS reporter gene was observed in plants under the control of Arabidopsis site II motif within a minimal promoter. This expression is strongly enhanced by addition of a telo box within this chimaeric promoter. We showed by gel retardation experiments that the site II motif is a target for several DNA-binding activities present in Arabidopsis crude cell extract and can bind a transcription factor, At-TCP20, from the Teosinte branched 1, Cycloidea, PCF (TCP)-domain protein family. In yeast two-hybrid experiments, At-TCP20 appears to be a potential partner of AtPura, which was previously shown to bind telo boxes. An important consequence of this analysis is to reveal new and conserved regulatory processes concerning the regulation of plant ribosomal gene expression in cycling cells. The implication of these observations in plant-speci®c developmental pathways is discussed.

As part of the goal to generate a detailed transcript map for Arabidopsis thaliana, 1152 single run sequences (expressed sequence tags or ESTs) have been determined from cDNA clones taken at random in libraries prepared from different sources of plant material: developing siliques, etiolated seedlings, flower buds, and cultured cells. Eight hundred and ninety-five different genes could be identified, 32% of which showed significant similarity to existing sequences in Arabidopsis and an array of other organisms. These sequences in combination with their positioning on the Arabidopsis genetic map will not only constitute a new set of molecular markers for genome analysis in Arabidopsis but also provide a direct route for the in vivo analysis of their gene products. The sequences have been made available to the public databases.

The gene family encoding the Arabidopsis thaliana translation elongation factor (EF-1 alpha) was analysed. This family contains four genes (A1-A4) organized in a similar manner in different varieties of Arabidopsis. Based upon both their physical separation and a comparison of their sequences, it is suggested that the A4 gene and the A1, A2, and A3 genes constitute two distinct subfamilies within the genome. By introducing chimaeric gene constructs into Arabidopsis cells, we showed that the A1 gene promoter mediates a transient expression about twofold higher than that obtained using the CaMV 35 S promoter. This expression depends on a 348 bp DNA fragment extending from -982 to -634 bp upstream of the initiation codon. This element contains a characteristic telomeric sequence (AACCCTAA) which is also found in the promoters of the A2 and A4 genes as well as in the promoters of the Drosophila EF-1 alpha F1 gene and of several highly expressed plant genes.

Nearly 7000 Arabidopsis thaliana-expressed sequence tags (ESTs) from 10 cDNA libraries have been sequenced, of which almost 5000 non-redundant tags have been submitted to the EMBL data bank. The quality of the cDNA libraries used is analysed. Similarity searches in international protein data banks have allowed the detection of significant similarities to a wide range of proteins from many organisms. Alignment with ESTs from the rice systematic sequencing project has allowed the detection of amino acid motifs which are conserved between the two organisms, thus identifying tags to genes encoding highly conserved proteins. These genes are candidates for a common framework in genome mapping projects in different plants.

SummaryThe promoters of Arabidopsis eEF1A genes contain a telomere motif, the telo-box, associated with an activating sequence, the tef-box. Database searches indicated the presence of telo-boxes in the 5¢ region of numerous genes encoding components of the translational apparatus. By using several promoter constructs we demonstrate that the telo-box is required for the expression of a b-glucoronidase gene in root primordia of transgenic Arabidopsis. This effect was observed when a telo-box was inserted upstream or downstream from the transcription initiation site, and occurred in synergy with the tef-box. These results clearly indicate that interstitial telomere motifs in plants are involved in control of gene expression. Southwestern screening of a lZAP library with a doublestranded Arabidopsis telomere motif resulted in characterization of a protein related to the conserved animal protein Pura. The possibility of a regulation process similar to that achieved by the Rap1p in Saccharomyces cerevisiae is discussed.