Three full-length cDNA clones, designated TRX1, TRX2, and TRX3 encoding different but similar thioredoxin h polypeptides, were isolated from sweet potato (Ipomoea batatas [L.] Lam `Tainong 57') storage roots. These three thioredoxin h clones were similar to each other and contained the canonical WCGPC active site and the important structural and functional amino acids that were conserved in thioredoxin sequences. Recombinant thioredoxin h (TRX2) overproduced in Escherichia coli (M15) was purified by Ni2+-chelated affinity chromatography. The molecular mass of TRX2 is ca. 1.4 kDa determined by SIDS-PAGE. TRX2 carries an N-terminal 17-amino acid extension enriched in hydrophobic residues. In Northern blot analysis, mRNAs corresponding to all three thioredoxin genes were found to have the highest level in the storage roots; those corresponding to TRX2 and TRX3 were detected at the next higher level in flowers. All three transcripts were detected at very low levels in sprouts of storage roots, roots, veins, and leaves. In Western blot analysis, the thioredoxins were found to have the highest level in the storage roots and veins; higher level in leaves; and very low levels in sprouts of storage root and roots. Active recombinant TRX2 protein is able to reduce the TI proteins in NTR system. Thioredoxin TRX2 was not reduced efficiently when NTR was removed from the NTR system. Three thioredoxin h genes of sweet potato storage roots display differential gene expression patterns, which may be associated with the diverse roles and functions they play in plant physiology in order to cope with particular developmental and environmental cues. (C) 2003 Elsevier Ireland Ltd. All rights reserved.
