MOLECULAR-CLONING AND CHARACTERIZATION OF ALDEHYDE OXIDASES IN ARABIDOPSIS-THALIANA

Using degenerate primers designed by deduced amino acid sequences of k nown aldehyde oxidases (AO) from maize and bovine, two independent cDN A fragments were amplified by reverse transcription-polymerase chain r eaction (PCR), The two corresponding full-length cDNAs (atAO-1 and atA O-2; 4,484 and 4,228 bp long, respectively) were cloned by screening t he Arabidopsis cDNA library followed by rapid amplification of cDNA en d-PCR, These cDNAs are highly homologous at both the nucleotide and am ino acid sequence levels, and the deduced amino acid sequences showed high similarity with those of maize and tomato AOs, They contain conse nsus sequences for two iron-sulfur centers and a molybdenum cofactor ( MoCo)-binding domain. In addition, another cDNA having a sequence simi lar to that of the cDNAs was screened (atAO-3; 3,049 bp), and a putati ve AO gene (AC002376) was reported on chromosome 1, which (atAO-4) was distinct from, but very similar to, the above three AOs, atAO-1, 2, 3 , and 4 were physically mapped on chromosomes 5, 3, 2 and 1, respectiv ely. These data indicate that there is an AO multigene family in Arabi dopsis, atAO-1 protein was shown to be highly similar to one of the ma ize AOs in respect to a region thought to be involved in determination of substrate specificity, suggesting that they might encode a similar type of AO, which could efficiently oxidize indole-3-acetaldehyde to indole-3-acetic acid (IAA), atAO-1 and atAO-2 genes were expressed at higher levels in lower hypocotyls and roots of the wild-type seedlings , while atAO-3 was slightly higher in cotyledons and upper hypocotyls, The expression of atAO-1 was more abundant in the seedlings of an IAA overproducing mutant (superroot1; sur1) than in those of wild type. a tAO-2 and atAO-3 transcripts were rather evenly distributed in these s eedlings. A possible involvement of atAO genes in phytohormone biosynt hesis in Arabidopsis is discussed.