Factors that influence Agrobacterium rhizogenes- mediated transformation of broccoli (Brassica oleracea L. var. italica)

An improved broccoli transformation system was developed by optimising several factors that affect the rate of effective Agrobacterium-mediated transformation. Leaf explants of cultivar Shogun were co-cultivated with Agrobacterium rhizogenes strain A4T harbouring the binary vector pART278. The T-DNA of this binary vector contains a neomycin phosphotransferase II (NOS-NPTII-NOS) gene for kanamycin resistance and a β-glucuronidase (35S-GUS-OCS) gene. Several media and factors were evaluated including combinations of arginine, mannopine, acetosyringone and the use of feeder cell layers. The new protocol includes the use of 200 μM acetosyringone in LB medium for bacterial growth, the use of a Brassica campestris feeder cell layer, 10 mM mannopine and 50 μM acetosyringone in the co-cultivation medium and 1 mM arginine in the selection medium. The use of this optimised protocol produced transformation rates of 33% in preliminary experiments transforming broccoli with the antisense 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase gene from pTOM13.