Wound-induced and developmental activation of a poplar tree chitinase gene promoter in transgenic tobacco.

Wounding hybrid poplar (Populus trichocarpa x P. deltoides) trees results in the expression of novel wound-inducible (win) mRNAs thought to encode proteins involved in defense against pests and pathogens. Members of the win6 gene family encode acidic multi-domain chitinases, with combined structure and charge characteristics that differ from previously described chitinases. Win6 expression has been shown to occur in pooled unwounded leaves of a wounded (on multiple leaves) poplar plant. Here we demonstrate that wounding a single leaf induces win6 expression locally, in the wounded leaf, and remotely, in specific unwounded leaves with strong vascular connections to the wounded leaf. We also demonstrate that a win6 promoter-beta-glucuronidase (GUS) gene fusion (win6-GUS) responds to wounding locally and remotely in transgenic tobacco. These data indicate that the poplar win6 promoter has regulatory elements that are responsive to 'wound signals' in the heterologous host. In addition, win6-GUS is developmentally activated in unwounded young leaves and floral tissues of transgenic tobacco. Similar developmental expression patterns are found to occur for win6 in poplar trees, demonstrating that a herbaceous plant can serve as a host for woody tree transgene analysis and can accurately predict expression patterns in tree tissues (e.g. flowers) that would be difficult to study in free-living trees.