Vascular expression of a bean cell wall glycine-rich protein-β-glucuronidase gene fusion in transgenic tobacco

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Abstract
In French bean (Phaseolus vulgaris L.), the glycine‐rich wall protein GRP 1.8 is specifically synthesized in protoxylem tracheary elements of the vascular system. A 494 bp upstream promoter fragment of the gene encoding GRP 1.8 was isolated and translationally fused to the β‐glucuronidase reporter gene. Transgenic tobacco plants containing this construct expressed the gene in vascular tissue of roots, stems, leaves and flowers. The gene was developmentally expressed during differentiation of both primary and secondary vascular tissue and was also rapidly induced (in < 30 min) after excision‐wounding of young stems. This wound response is more rapid than in bean hypocotyls, indicating possible differences between the activation mechanism for glycine‐rich protein gene expression in wounded bean and tobacco. Only a subset of cells were found to participate in the wound response. In young stems, the GRP wound induction was localized in pith parenchyma cells adjacent to the wound surface, where vessel regeneration is known to occur. Thus, a promoter fragment of 494 bp, including 427 bp upstream from the transcription start site, contains information for tissue‐specific and wound‐induced gene regulation. The cell‐type specificity of expression suggests that the GRP 1.8 promoter is regulated by very specific developmental and environmental signals.