The laccase promoter of potato confers strong tuber-specific expression in transgenic plants

Tissue-specific promoters for efficient expression of transgenes at specific times or in specific plant tissues can be applied to develop new transgenic plants. To exploit a promoter capable of driving strong expression in potato tubers, we isolated the promoter region of the laccase gene from potato (Solanum tuberosum L. cv. Desiree) and characterized its activity in transgenic Solanaceae plants, such as potato, tobacco and tomato. The ability of the laccase promoter to induce the beta-glucuronidase (GUS) reporter was evaluated in independent transgenic potato lines and compared with that of the constitutive CaMV35S promoter. To determine the tissue specificity of expression in transgenic potato, GUS levels in shoot tips, leaves, stems, roots and tubers were measured by histochemical analysis. The laccase promoter conferred tuber-specific expression in transgenic potato regardless of the developmental stage, and there was no GUS reporter expression in leaves, stems or roots. Serial 5' deletion analysis of the laccase promoter revealed that the tuber-specific regulatory elements might be scattered throughout the promoter. The laccase promoter responded weakly to salt stress, mannitol stress, and mechanical wounding but not to cold stress in the leaves and stems of transgenic potato. In transgenic tobacco, weak GUS expression driven by the laccase promoter was detected throughout the entire plant, whereas in transgenic tomato, GUS expression was detected only in the roots and seeds. Our data show that the laccase promoter represents a feasible candidate to drive high and preferential expression of genes in potato tubers.