Competence of Arabidopsis thaliana genotypes and mutants for Agrobacterium tumefaciens‐mediated gene transfer: role of phytohormones

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Abstract
Many plant species and/or genotypes are highly recalcitrant to Agrobacterium‐mediated genetic transformation, and yet little is known about this phenomenon. Using several Arabidopsis genotypes/ecotypes, the results of this study indicated that phytohormone pretreatment could overcome this recalcitrance by increasing the transformation rate in the known recalcitrant genotypes. Transient expression of a T‐DNA encoded β‐glucuronidase (GUS) gene and stable kanamycin resistance were obtained for the ten Arabidopsis genotypes tested as well as for the mutant uvh1 (up to 69% of petioles with blue spots and up to 42% resistant calli). Cultivation of Arabidopsis tissues on phytohormones for 2–8 d before co‐cultivation with Agrobacterium tumefaciens significantly increased transient GUS gene expression by 2–11‐fold and stable T‐DNA integration with petiole explants. Different Arabidopsis ecotypes revealed differences in their susceptibility to Agrobacterium‐mediated transformation and in their type of reaction to pre‐cultivation (three types of reactions were defined by gathering ecotypes into three groups). The Arabidopsis uvh1 mutant described as defective in a DNA repair system showed slightly lower competence to transformation than did its progenitor Colombia. This reduced transformation competence, however, could be overcome by 4‐d pre‐culture with phytohormones. The importance of pre‐cultivation with phytohormones for genetic transformation is discussed.