Establishment of an efficient alfalfa regeneration system via organogenesis and the co-expression of Arabidopsis SOS genes improves salt tolerance in transgenic alfalfa (Medicago sativa L.)

The Salt Overly Sensitive (SOS) signal transduction pathway is pivotal in Na+ efflux and facilitates ion transport and homeostasis for improved salt tolerance in plants. Ten alfalfa varieties were used as experimental materials, and two alfalfa regeneration systems were established and optimized. Cotyledons and hypocotyls were initially used as explants to induce embryogenic callus via the indirect production of somatic embryos in order to establish a callus acceptor system. Cotyledonary nodes were used as explants to induce adventitious bud formation via direct organogenesis, thereby establishing an in vitro regeneration system that could be used for the genetic transformation. Agrobacterium-mediated transformation of the cotyledonary nodes of the alfalfa cv. “Golden Empress b” was used to generate 25 independent sources of transformed plants exhibiting herbicide tolerance. Four of the positive transgenic plants were randomly selected for southern blot analysis, and three hybridization signals with one o...