MODULAR ORGANIZATION AND DEVELOPMENTAL ACTIVITY OF AN ARABIDOPSIS-THALIANA EF-1-ALPHA GENE PROMOTER

The activity of the Arabidopsis thalana A1 EF-1alpha gene promoter was analyzed in transgenic Arabidopsis plants. The 5' upstream sequence o f the A1 gene and several promoter deletions were fused to the beta-gl ucuronidase (GUS) coding region. Promoter activity was monitored by qu antitative and histochemical assays of GUS activity. The results show that the A1 promoter exhibits a modular organization. Sequences both u pstream and downstream relative to the transcription initiation site a re involved in quantitative and tissue-specific expression during vege tative growth. One upstream element may be involved in the activation of expression in meristematic tissues; the downstream region, correspo nding to an intron within the 5' non-coding region (5'IVS), is importa nt for expression in roots; both upstream and downstream sequences are required for expression in leaves, suggesting combinatorial propertie s of EF-1alpha cis-regulatory elements. This notion of specific combin atorial regulation is reinforced by the results of transient expressio n experiments in transfected Arabidopsis protoplasts. The deletion of the 5'IVS has much more effect on expression when the promoter activit y is under the control of A1 EF-1alpha upstream sequences than when th ese upstream sequences were replaced by the 35S enhancer. Similarly, a synthetic oligonucleotide corresponding to an A1 EF-1alpha upstream c is-acting element (the TEF1 box), is able to restore partially the ori ginal activity when fused to a TEF1-less EF1-alpha promoter but has no significant effect when fused to an enhancer-less 35S promoter.