Chapter 5 - High-Efficiency Transformation Techniques

Abstract

Wheat, barley, oat, rye, and triticale generally exhibit superior tolerance to environmental stresses and poor soil conditions. These species were first transformed by direct DNA transfer in the 1990s, and then by Agrobacterium tumefaciens. Efforts were especially made in wheat and barley to optimize factors related to plant tissues, various treatments, culture media, selection markers, strains of A. tumefaciens, and transformation vectors so that highly efficient protocols were developed. In all of these species, A. tumefaciens strains derived from strain A281 and vectors carrying virulence genes from A281 gave higher efficiency of transformation, and the hygromycin resistance gene and the bar gene were chosen as selection markers. Immature embryos were the best starting tissues, but considerable investment is required to supply fresh tissues. Naturally, collaboration is recommended between users of the technology and elite teams focusing on the transformation of immature embryos. Deregulation cost and limited public acceptance are delaying commercialization of transgenic varieties, and gene editing, which requires techniques mostly shared by transformation, is an attractive option. A major hurdle is the fact that limited genotypes are amenable to tissue culture. Both protocol improvement and exploitation of genes related to good tissue culture response must be further pursued.