TISSUE-SPECIFIC EXPRESSION AND PROMOTER ANALYSIS OF THE TOBACCO ITP1 GENE

The Nicotiana tabacum ltp1 gene (Ntltp1) encodes a small basic protein that belongs to a class of putative lipid transfer proteins. These pr oteins transfer lipids between membranes in vitro, but their in vivo f unction remains hotly debated. This gene also serves as an important e arly marker for epidermis differentiation. We report here the analysis of the spatial and developmental activity of the Ntltp1 promoter, and we define a sequence element required for epidermis-specific expressi on. Transgenic plants were created containing 1346 bp of the Ntltp1 pr omoter fused upstream of the P-glucuronidase (GUS) gene. In the mature aerial tissues, GUS activity was detected predominantly in the epider mis, whereas in younger aerial tissues, such as the shoot apical meris tem and floral meristem, GUS expression was not restricted to the tuni ca layer. Unexpectedly, GUS activity was also detected in young roots, particularly in the root epidermis. Furthermore, the Ntltp1 promoter displayed a tissue and developmental specific pattern of activity duri ng germination. These results suggest that the Ntltp1 gene is highly e xpressed in regions of the plant that are vulnerable to pathogen attac k and are thus consistent with the proposed function of lipid transfer proteins in plant defense. Deletions of the promoter from its 5' end revealed that the 148 bp preceding the translational start site are su fficient for epidermis-specific expression. Sequence comparison identi fied an eight-nucleotide palindromic sequence CTAGCTAG in the leader o f Ntltp1, which is conserved in a number of other ltp genes. By gel re tardation analysis, the presence of specific DNA-protein complexes in this region was demonstrated. The characterization of these factors ma y lead to the identification of factors that control early events in e pidermis differentiation.