Sorghum genetic transformation by particle bombardment

Particle bombardment transformation describes the acceleration of high-velocity microparticles coated with exotic genes through the plant-protective cell walls, in order for the introduced genes to be integrated into the host genome. This technique has proven to be an effective and versatile approach towards plant genetic modification in preceding decades. Particle bombardment has been successfully applied to cereals including rice, maize, wheat, barley, and sorghum. Historically, sorghum has been considered as one of the most recalcitrant major crops with regard to successful genetic transformation; however, tremendous progress has been made in recent years. Transformation efficiency by particle bombardment has now improved from approximately 1 % to in excess of 20 % utilizing an optimized tissue culture and DNA delivery system. The protocol described in this chapter routinely generates transformants at 10-25 % efficiency within sorghum genotype Tx430. The process generally takes 11-16 weeks from initiation of immature embryos to planting of transformants. This protocol covers the operation of both the Bio-Rad PDS-1000/He System and particle inflow gun. Three factors are crucial to an efficient particle bombardment transformation system: (1) an efficient tissue culture system, (2) a highly efficient DNA delivery system, and (3) an effective selection strategy.