Agrobacterium-mediated transformation of soybean: Test of selectable marker genes

Soybean (Glycine max) is one of the most important crops around the world. Genetic modification of soybean offers an alternative way to augment the traditional soybean breeding approaches. Soybean transformation still remains a great challenge. To increase soybean transformation efficiency, three selectable marker genes, bar, ALS and ASA2 , were tested with two soybean transformation systems, e.g. cotyledonary nodes and mature embryo axes systems, with glufosinate, Arsenal and 5-MT as the selective agents, respectively. Transgenic soybean lines have been generated using all three selectable markers and molecular analyses confirmed the integration of the transgenes into the soybean genome. Progeny analyses of these transgenic lines demonstrated that the transgenes were inherited in a Mendelian fashion and the transgenic plants showed resistance to the corresponding selection agents, glufosinate and Arsenal. A comparison of the two transformation systems shows the embryo axes system is more efficient since cotyledonary node transformation system takes at least 3 months to obtain transgenic shoots while the embryo axes system only takes about one month. Of the three selectable marker genes tested for soybean transformation, the ASA2 gene has the potential to be used as a novel and publically acceptable selectable marker for developing transgenic soybeans with potential commercial use.