Kenichi Takane

Two Distinct Uricase II (Nodulin 35) Genes Are Differentially Expressed in Soybean Plants

Nodule-specific uricase (uricase II) is a homotetramer of a 33-kDa polypeptide, nodulin 35, and plays a key role in the assimilation of nitrogen fixed by microsymbionts in most legumes that have determinate nodules. We have isolated two distinct genes, UR2 and UR9, that encode for nodulin 35 from a soybean genomic library. Their corresponding cDNAs were also isolated from a nodule cDNA library. UR2 and UR9 both encode for 309 amino acid proteins with 12 amino acid differences. The expression of these two genes in various organs of soybean was examined by reverse transcription-polymerase chain reaction with primers specific to each cDNA sequences. Expression of UR9 was almost specific in root nodules, although it was expressed in roots, primary leaves, and developing seed at very low levels. In contrast, the UR2 transcripts were present in almost all plant organs at low levels, but no enhancement of the expression was observed in nodules. Thus, UR9 behaves as a nodulin gene, whereas UR2 is a nonsymbiotic uricase II gene. The sequences of their potential promoter regions share high homology within regions up to about 400 bp upstream from the translation initiation sites. These results suggest that symbiotic and nonsymbiotic uricase II genes diverged by gene duplication and that relatively small alterations in the promoter sequence enable the nodule-specific expression.

Structural and Expression Analysis of Uricase mRNA from Lotus japonicus

Uricase (nodulin-35) cDNA, LjUr, was isolated from nodules of a model legume, Lotus japonicus. LjUr expression was most abundant in nodules, although it was detected in nonsymbiotic tissues as well, particularly in roots. Expression in nodules was detected in uninfected cells, nodule parenchyma, and, more intensely, in vascular bundles. Phylogenetic analysis of uricase sequences from various legumes indicated that uricases of amide- and ureide-transporting legumes form two distinct clades. LjUr is in the cluster of amide-transport legumes even though L. japonicus bears determinate nodules.

Symbiotic Nitrogen Fixation at the Late Stage of Nodule Formation in Lotus japonicus and Other Legume Plants

Lotus japonicus nodules are reviewed, and current research data on Nod-35 (uricase) gene, including that of Lotus japonicus as an example of a late nodulin gene are presented.

Expression of Two Uricase Genes and the Promoter Analysis Using Transgenic Hairy Roots

Uricase (homotetramer of nodulin 35) is one of the major proteins in soybean nodules, and the physiological role is significant for producing ureides as major compounds to export the fixed nitrogen to the shoots.

Uninfected cell specific enhancement of a nodulin-35 genomic gene expression in soybean nodules. Evidences by RT-PCR and chimeric promoter region: GUS reporter gene analysis using transgenic hairy root system of soybean

Uricase II (nodulin-35) is believed to regulate allantoin biosynthesis in nodules of various legumes. The mechanisms of nodule-specific enhancement of nodulin-35 gene expression were studied in soybeans (Glycine max. L. cv. akisengoku). Northern blot hybridization assay detected only very low levels of nodulin-35 gene expression in various non-symbiotic tissues of soybean plants; only in nodule tissues was the expression enhanced significantly. RT-PCR assay showing enhanced nodulin-35 expression was observed in only one (UR9) of two nodulin-35 genes (UR2 and UR9) in the soybean genome.