Inhibition of Agrobacterium-Induced Cell Death by Antiapoptotic Gene Expression Leads to Very High Transformation Efficiency of Banana

Abstract

The death of plant cells in culture following exposure to Agrobacterium tumefaciens remains a major obstacle in de- veloping Agrobacterium-mediated transformation into a highly efficient genotype-independent technology. Here, we present evidence that A. tumefaciens exposure induces cell death in banana cell suspensions. More than 90% of em- bryogenic banana cells died after exposure to A. tumefaciens and cell death was accompanied by a subset of features associated with apoptosis in mammalian cells, including DNA laddering, fragmentation, and formation of apoptotic- like bodies. Importantly, these cellular responses were inhibited in cells expressing the animal antiapoptosis genes Bcl-xL, Bcl-2 3′ untranslated region, and CED-9. Inhibition of cell death resulted in up to 90% of cell clumps trans- formed with Bcl-xL, a 100-fold enhancement over vector controls, approaching the transformation and regeneration of every “transformable” cell. Similar results using sugar- cane, a crop plant known for recalcitrance to Agrobacterium transformation, suggest that antiapoptosis genes may inhibit these phenomena and increase the transformation frequency of many recalcitrant plant species, including the major monocot cereal crop plants. Evidence of inhibition of plant cell death by cross-kingdom antiapoptotic genes also contributes to the growing evidence that genes for con- trol of programmed cell death are conserved across wide evolutionary distances, even though these mechanisms are not well understood in plants.