Further progress towards a catalogue of all Arabidopsis genes: analysis of a set of 5000 non-redundant ESTs.

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.

Cis-acting elements and expression pattern of the spinach rps22 gene coding for a plastid-specific ribosomal protein.

In order to study the regulation of nuclear genes coding for plastid ribosomal proteins, we have analysed the promoter region of spinach rps22 using both in vitro and in vivo approaches. By footprinting analyses, we have identified eight DNA elements interacting with spinach leaf nuclear factors in the 300 bp promoter region upstream of the transcription start site. Among these elements, four are short AT-rich sequences and one is identical to the Hex motif characterized initially in wheat histone genes. In transgenic tobacco plants, the reporter gene coding for the beta-glucuronidase (GUS) directed by a 1.2 kb upstream region of rps22 was expressed in several plant organs, with high levels in leaf mesophyll, embryo cotyledons and root meristematic cells and very low levels in other cell types. Interestingly, when deleted to -295, the promoter, which contained all the foot-printed elements, was still able to confer the same expression pattern, although the activity was relatively lower than with the 1.2 kb promoter. When deleted further to -154, the promoter, from which the AT-rich elements were eliminated, loses its activity almost completely, suggesting that these AT-rich elements are important for the rps22 promoter activity. Altogether, our results show that rps22 gene expression is controlled by specific cis elements not present in other nuclear-encoded plastid ribosomal protein genes studied so far.

S1F binding site is related to but different from the light-responsive GT-1 binding site and differentially represses the spinach rps1 promoter in transgenic tobacco.

Nuclear genes encoding plastid ribosomal proteins are more highly expressed in leaves than in roots. This leaf-specific induction seems to be light-independent. We have previously characterized a spinach nuclear factor S1F binding to a cis-element within the rps1 promoter, which negatively regulates both the rps1 and the cauliflower mosaic virus 35S promoters in transient expression assays. Here, we show that the S1F binding site is related to but different from the light-responsive Box II of the pea rbcS-3A promoter, which is recognized by the nuclear factor GT-1. Transgenic plant analyses showed that the S1F site tissue-specifically represses the rps1 promoter in roots as well as in etiolated seedlings. We suggest that the GT-1-related S1F binding site is responsible, at least in part, for the transcriptional repression of rps1 in nonphotosynthetic tissues such as roots.