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.

In an Arabidopsis thaliana T87-C3 cell-suspension culture, entry into the growth-arrest phase is rapidly followed by a loss of cell viability. Three cDNA clones, SRGI, SRG2, and SRG3, corresponding to genes with transcripts that accumulate during these late phases, were isolated by the mRNA differential display method. Amino acid sequence analysis shows that the putative SRCl protein is a new member of the Fe(ll)/ascorbate oxidase superfamily, and that SRG2 codes for a protein with significant homology to P-glucosidases. Significantly, all three SRG genes are expressed in senescing organs of Arabidopsis plants. Two previously characterized genes, SAG2 and SAG4, induced during natural senescence in Arabidopsis, were also found to be expressed in cell-suspension cultures and have expression kinetics similar to those observed for the SRGl gene. Taken together these findings suggest that certain molecular events are common to both plant senescence and growth arrest in Arabidopsis cell suspensions. Both internucleosomal cleavage of nDNA and an apparent compaction of chromatin, two characteristic features of programmed cell death in animal cells, have been observed in Arabidopsis cell cultures at a stage corresponding to loss of cell viability. ~~ ~Cultured cells are now universally recognized as appropriate model systems with which to investigate the molecular responses of plants to stimuli that affect growth, such as nutrient availability (e.g. Roitsch et al., 1995) and plant growth factor requirements (e.g. Teyssendier de la Serve et al., 1985;Dominov et al., 1992;Lee and Chen, 1993). For example, limitations in phosphate concentration (Kodama et al., 1990;Kock et al., 1995; Malboobi and Lefebvre, 1995), nitrogen supply (Kodama et al., 1990), carbon source (Kodama et al., 1990;Sheu et al., 1994;Hsieh et al., 1995;Tseng et al., 1995), or hormone depletion (Crowell and Amasino, 1991) result in modifications in gene expression, leading to changes in the cellular mRNA pattern.After nutrient exhaustion, certain cell cultures undergo rapid growth arrest, followed by a dramatic loss of viabil- ity. We are currently studying these late phases of the cell culture growth cycle, which exhibit a number of morphological symptoms similar to those that occur in senescing plant tissues, which have recently been described in sugarstarved, cultured rice cells (Chen et al., 1994).As a first step toward characterizing the molecular events associated with growth arrest and viability loss, we have attempted to select genes with a relative expression that is enhanced at the end of the growth phase of the cell culture. For this purpose, we chose an Arabidopsis fkaliana cell line (Axelos et al., 1992) with a particularly short growth-arrest period. Transcripts that accumulated at the end of the growth phase of the culture were characterized by the mRNA differential display method (Liang and Pardee, 1992). Three cDNA clones were isolated and the expression patterns of the corresponding genes were analyzed both throughout the cell culture gr...