Rapid and reproducible Agrobacterium-mediated transformation of sorghum

A rapid and reproducible Agrobacterium-mediated transformation protocol for sorghum has been developed. The protocol uses the nptII selectable marker gene with either of the aminoglycosides geneticin or paromomycin. A screen of various A. tumefaciens strains revealed that a novel C58 nopaline chromosomal background carrying the chrysanthopine disarmed Ti plasmid pTiKPSF₂, designated NTL₄/Chry5, was most efficient for gene transfer to sorghum immature embryos. A NTL₄/Chry5 transconjugant harboring the pPTN290 binary plasmid, which carries nptII and GUSPlus ^TM expression cassettes, was used in a series of stable transformation experiments with Tx430 and C2-97 sorghum genotypes and approximately 80% of these transformation experiments resulted in the recovery of at least one transgenic event. The transformation frequencies among the successful experiments ranged from 0.3 to 4.5%, with the average transformation frequency being approximately 1% for both genotypes. Over 97% of the transgenic events were successfully established in the greenhouse and were fully fertile. Co-expression of GUSPlus ^TM occurred in 89% of the transgenic T₀ events. Seed set for the primary transgenic plants ranged from 145 to 1400 seed/plant. Analysis of T₁ progeny demonstrated transmission of the transgenes in a simple Mendelian fashion in the majority of events.