Arabidopsis loss-of-function mutant in the lysine pathway points out complex regulation mechanisms

In plants, the amino acids lysine, threonine, methionine and isoleucine hav e L-aspartate-P-semialdehyde (ASA) as a common precursor in their biosynthe sis pathways. How this ASA precursor is dispersed among the different pathw ays remains vague knowledge. The proportional balances of free and/or prote in-bound lysine, threonine, isoleucine and methionine are a function of pro tein synthesis, secondary metabolism and plant physiology. Some control poi nts determining the flux: through the distinct pathways are known, but an a dequate explanation of how the competing pathways share ASA in a fine-tuned amino acid biosynthesis network is yet not available. In this article me d iscuss the influence of lysine biosynthesis on the adjacent pathways of thr eonine and methionine, We report the finding of an Al Arabidopsis thaliana dihydrodipicolinate synthase T-DNA insertion mutant displaying lower lysine synthesis, and, as a result of this, a strongly enhanced synthesis of thre onine, Consequences of these cross-pathway regulations are discussed. (C) 2 000 Federation of European Biochemical Societies, Published by Elsevier Sci ence B.V. All rights reserved.