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 transcripti onally activated in the bacteria by plant metabolites released from th e wound site. Hence, it is believed that agrobacteria use injuries to facilitate their entrance into the host plant and that the wounded sta te is required for plant cell competence for Agrobacterium-mediated ge ne delivery. However, our experiments using vir gene-activated bacteri a sprayed onto tobacco plantlets demonstrated that cells in unwounded plants could also be efficiently transformed. The condition of the pla nt 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 appl ied to the plant. Under these experimental conditions, stomatal openin g seems to be used by Agrobacterium to circumvent the physical barrier of the cuticle. These results thus show that the proposed cellular re sponses evoked by wounding in higher plants are not essential for Agro bacterium-mediated transformation.