Transfer and Integration of T-DNA without Cell Injury in the Host Plant.

Agrobacterium colonizes plant cells via a gene transfer mechanism that results in plant tumorigenesis. Virulence (vir) genes are transcriptionally activated in the bacteria by plant metabolites released from the wound site. Hence, it is believed that agrobacteria use injuries to facilitate their entrance into the host plant and that the wounded state is required for plant cell competence for Agrobacterium-mediated gene delivery. However, our experiments using vir gene-activated bacteria sprayed onto tobacco plantlets demonstrated that cells in unwounded plants could also be efficiently transformed. The condition of the plant cells was monitored using [beta]-glucuronidase under the control of a wound-inducible promoter. Infection of leaf tissue is light dependent, and it is drastically reduced when abscisic acid is exogenously applied to the plant. Under these experimental conditions, stomatal opening seems to be used by Agrobacterium to circumvent the physical barrier of the cuticle. These results thus show that the proposed cellular responses evoked by wounding in higher plants are not essential for Agrobacterium-mediated transformation.