Regeneration from mature and immature embryos and transient gene expression via Agrobacterium-mediated transformation in emmer wheat (Triticum dicoccum Schuble)

Abstract

The present study establishes a regeneration protocol and optimizes conditions for Agrobacterium-mediated transformation of the tetraploid emmer wheat, Triticum dicoccum. Regeneration from mature and immature embryos was accomplished as a two-step process involving callus induction in the presence of 2,4-D followed by regeneration on a 2,4-D free, cytokinin-containing medium (RM1). Higher concentrations of 2,4-D (4 mg/l) though conducive for callusing (89.39% in mature embryos and 96% in immature embryos) proved detrimental for further regeneration. At lower 2,4-D (1 mg/ml) although callusing was suboptimal, (56.8% and 84% from mature and immature embryos, respectively) the regeneration response was the highest on RM1 medium (64.4% and 56.6% from mature and immature embryos, respectively). Overall, the regeneration response of immature embryos was lower than the mature embryos by 10-12%. Due to the ease of availability of mature embryos the mature embryo-derived calli were chosen as the target tissue for Agrobacterium-mediated transformation in the two Indian varieties DDK1001 and DDK1009. Histochemical GUS expression revealed the suitability of the mature embryo-derived calli for such investigations. Of the CaMV35S and Act1 promoters employed, the monocot promoter Act1 displayed higher GUS gene activity in the mature embryo derived calli when co-cultivated with LBA4404 (pBI101::Act1).