Establishment of neomycin phosphotransferase II (nptII) selection for transformation of soybean somatic embryogenic cultures

Abstract

Soybean transformation is limited by the lack of multiple efficient selectable marker systems. Biolistic transformation of somatic proliferative embryogenic cultures, one of the commonly used soybean transformation methods, relies largely on hygromycin phosphotransferase II (hptII) selection. The purpose of the present study was to establish another efficient selectable marker system to facilitate multiple gene transformations of soybean. We tested neomycin phosphotransferase II (nptII) that has been used successfully in cotyledonary node transformation, but with limited success in transformation of embryogenic cultures. Transgenic events were obtained using nptII with improved G418 selection without generating escapes. G418 selection required longer recovery and selection periods, and resulted in a lower efficiency of initial transformants compared to hygromycin selection. Six independent fertile transgenic plants were recovered using nptII and G418, a frequency similar to that obtained with hygromycin selection. Soybean embryogenic cultures co-transformed with the hptII and nptII markers showed resistance to both hygromycin B and G418, while regeneration and plant fertility were not adversely affected. The nptII will be useful as a second selectable marker for multiple gene transformations in basic and applied soybean research.