Molecular cloning and characterization of adr and ivd genes from Frankia EuIK1 strain

The nucleotide sequences of adrenodoxin reductase (adr) gene and isovaleryl-CoA dehydrogenase (ivd) gene and the expression pattern of adr from Frankia EuIK1 strain, symbiont of Elaeagnus umbellata, were determined. 5.5-kb NotI, 5.5-kb SacI, 1.3-kb SacI restriction fragments of pEuAR1, a cosmid clone hybridized with a squalene-hopene cyclase (shc) DNA probe, were subcloned and partially sequenced. Sequence analysis showed three fragments to overlap and harbor adr and ivd genes but not the targeted shc gene. The deduced amino acid sequence of AdR, consisting of 487 amino acids, showed sequence similarity of about 55% with other AdRs, and that of ivd, consisting of 384 amino acids, showed about 60% similarity with others. RT-PCR experiments revealed that the expression of adr was in low level at 6 weeks after inoculation (WAI), reached peak at 8 WAI, and decreased to some extent at 10 WAI. AdR is a probable redox partner of [2Fe–2S] ferredoxin involved in the biosynthesis of Fe/S cluster for cellular Fe/S proteins and also could be involved in nitrogen-fixation. It is the first report about adr and ivd in Frankia.