Vectors used. (a) and (b): pBract vectors. (a). pBract203 destination vector containing the hpt gene under the control of a CaMV 35s promoter together with the chlormaphenicol resistance gene and the negative selection ccdB gene flanked by attR Gateway recombination sites. (b). pBract215 expression vector, created by cloning a luciferase cassette into pBract203 (via Gateway recombination). This construct contains the hpt gene under the control of a CaMV 35s promoter together with the luciferase gene under the control of a maize ubiquitin promoter (ubi1). (c): pSoup containing pSa-RepA (a component of the Agrobacterium replication origin), the replicase gene trfA, a tetracycline resistance gene (tetR), a broad-host range origin of replication (pRK2) and a multiple cloning site.