Transient expression of ipt gene enhances regeneration and transformation rates of sunflower shoot apices (Helianthus annuus L.)

The limiting step in the transformation protocol for sunflower (Helianthus annuus L.) is the induction of adventitious shoots from embryonic axes. This specific element of an established protocol was addressed in the present study. The explants were bombarded with tungsten particles coated with a construct harbouring the ipt gene of Agrobacterium vitis, involved in the de novo synthesis of cytokinins, in addition to the usual co-culture with an Agrobacterium strain harbouring the gene of interest, i.e. the uidA gene. The proportion of GUS-expressing shoots was increased in the bombarded samples. The expression of the ipt gene was transient and the construct was not incorporated in the regenerated shoots. After introduction of this additional step in the transformation protocol, the rate of recovery of transgenic shoots after Agrobacterium-mediated transformation was 6.2%, corresponding to approximately 3 times the control value obtained in experiments without the additional bombardment step or where explants were bombarded with naked particles.