Stability of transgene expression, field performance and recombination breeding of transformed barley lines

Stable inheritance of the transgene, consistent expression and competitive agronomic properties of transgenic crops are important parameters for succe ssful use of the latter. These properties have been analyzed with 18 homozy gous transgenic barley lines of the cultivar Golden Promise. The lines orig inated from three independent primary transformants obtained by the biolist ic method with three plasmids containing respectively, the bar gene, the ui dA gene and the gene for a protein-engineered heat-stable (1,3-1,4)-beta -g lucanase. Three production levels of recombinant beta -glucanase were ident ified in homozygous transgenic T-3 plants, and these remained constant over a 3-year period. In micro-malting experiments, the heat-stable enzyme reac hed levels of up to 1.4 mug.mg(-1) protein and survived kiln drying at leve ls of 70-100%. In the field trials of 1997 and 1998 the transgenic lines ha d a reduced 1000-grain weight as well as variable yield depressions compare d to the Golden Promise progenitor. In 1999 large-scale propagations of the lines with the highest recombinant enzyme synthesis during germination and of Golden Promise were studied at three different locations. Tn an irrigat ed field transgenic lines yielded approximately 6 t.ha(-1) and Golden Promi se 7.7 t.ha(-1). Cross-breeding was carried out to transfer the transgene i nto a more suitable genetic background. Crosses of the semi-dwarf ari-e mut ant Golden Promise gave rise to the four morphological phenotypes nutans, h igh erect, erect, and ari-e. Two improvements were achieved: (1) F-3 lines homozygous for the expression of heat-stable (1,3-1,4)-beta -glucanase were found among lines that were homozygous for each of the four morphological phenotypes; (2) improved 1000-grainweights and yields with respect to those of the original transformants were observed in some F-4 lines homozygous f or the morphological phenotypes and for the transgene. In the case of a hom ozygous nutans line, the transgenic plants had a higher 1000-grain weight t han those lacking the transgene. Like mutants providing useful output trait s, transgenic plants will often have to be improved by relocating the gene into more suitable genotypes.