Leucine and its keto acid enhance the coordinated expression of genes for branched-chain amino acid catabolism in Arabidopsis under sugar starvation

Branched-chain alpha -keto acid dehydrogenase (BCKDH), a multienzyme complex, plays a key role in branched-chain amino acid catabolism. However cr, it remains unclear whether expression of each subunit is coordinately regulated in plants, which should be important for the efficient assembly of subunits into a functional multienzyme complex. We show that the transcripts from the. ll Arabidopsis Ela subunit gene accumulated in dark-adapted leaves and in sugar-starved suspension cells. These results are complementary to our previous report that the transcripts for the Ela and E2 subunit genes accumulated in sugar-starved cells. Expression of the Ela gene is likely to be regulated by hexokinase-mediated sugar signaling, indicating that sugar plays a regulatory role in the coordinated expression of BCKDH subunit genes. Furthermore, Leu and its metabolite alpha -ketoisocaproate have synergistic effects on the enhanced expression of BCKDH( subunit genes under sugar starvation. We hence suggest that branched-chain amino acids activate their own degradation pathway in sugar-starved cells through coinduction of each subunit gene of BCKDH. (C) 2001 Published by Elsevier Science B.V. on behalf of the Federation of European Biochemical Societies.