ENGINEERING OF THE ASPARTATE FAMILY BIOSYNTHETIC-PATHWAY IN BARLEY (HORDEUM-VULGARE L) BY TRANSFORMATION WITH HETEROLOGOUS GENES ENCODING FEED-BACK-INSENSITIVE ASPARTATE KINASE AND DIHYDRODIPICOLINATE SYNTHASE

In prokaryotes and plants the synthesis of the essential amino acids l ysine and threonine is predominantly regulated by feed-back inhibition of aspartate kinase (AK) and dihydrodipicolinate synthase (DHPS). In order to modify the flux through the aspartate family pathway in barle y and enhance the accumulation of the corresponding amino acids, we ha ve generated transgenic barley plants that constitutively express muta nt Escherichia coli genes encoding lysine feed-back insensitive forms of AK and DHPS. As a result, leaves of primary transformants (T-0) exh ibited a 14-fold increase of free lysine and an 8-fold increase in fre e methionine. In mature seeds of the DHPS transgenics, there was a 2-f old increase in free lysine, arginine and asparagine and a 50% reducti on in free proline, while no changes were observed in the seeds of the two AK transgenic lines analysed. When compared to that of control se eds, no differences were observed in the composition of total amino ac ids. The introduced genes were inherited in the T-1 generation where e nzymic activities revealed a 2.3-fold increase of AK activity and a 4. 0-9.5-fold increase for DHPS. T-1 seeds of DHPS transformants showed t he same changes in free amino acids as observed in T-0 seeds. It is co ncluded that the aspartate family pathway may be genetically engineere d by the introduction of genes coding for feed-back-insensitive enzyme s, preferentially giving elevated levels of lysine and methionine.