Characterization of two cDNAs encoding mitochondrial lipoamide dehydrogenase from arabidopsis

In contrast to peas (Pisum sativum), where mitochondrial lipoamide dehydrog enase is encoded by a single gene and shared between the ce-ketoacid dehydr ogenase complexes and the Gly decarboxylase complex, Arabidopsis has two ge nes encoding for two mitochondrial lipoamide dehydrogenases. Northern-blot analysis revealed different levels of RNA expression for the two genes in d ifferent organs; mtLPD1 had higher RNA levels in green leaves compared with the much lower level in roots. The mRNA for mtLPD2 shows the inverse patte rn. The other organs examined showed nearly equal RNA expressions for both genes. Analysis of etiolated seedlings transferred to light showed a strong induction of RNA expression for mtLPD1 but only a moderate induction of mt LPD2. Based on the organ and light-dependent expression patterns, we hypoth esize that mtLPD1 encodes the protein most often associated with the Gly de carboxylase complex, and mtLPD2 encodes the protein incorporated into a-ket oacid dehydrogenase complexes. Due to the high level of sequence conservati on between the two mtLPDs, we assume that the proteins, once in the mitocho ndrial matrix, are interchangeable among the different multienzyme complexe s. If present at high levels, one mtLPD might substitute for the other. Sup porting this hypothesis are results obtained with a T-DNA knockout mutant, mtlpd2, which shows no apparent phenotypic change under laboratory growth c onditions. This indicates that mtLPD1 can substitute for mtLPD2 and associa te with all these multienzyme complexes.