THE LOTUS-JAPONICUS LJNOD70 NODULIN GENE ENCODES A PROTEIN WITH SIMILARITIES TO TRANSPORTERS

A novel nodule-specific gene, LjNOD70, associated with late stages in Lotus japonicus nodule development and/or functioning was characterize d. The LjNOD70 gene is a member of a small family of closely related L . japonicus genes. Two major mRNA species corresponding to the LjNOD70 gene were identified in nodules and shown to be the result of a mecha nism resembling alternative splicing. The longer, presumably unspliced , mRNA species was shown to contain a single open reading frame (ORF), encoding a polytopic hydrophobic protein, LjN70, with a predicted mol ecular mass of 70 kDa. The second, presumably spliced, mRNA species wa s shown to be less abundant in nodules. The absence of the presumptive 'intron' was found to divide the reading frame into an upstream and a downstream ORF encoding the partial N- and C-terminal regions of the LjN70 protein, respectively. The predicted amino acid sequence of nodu lin LjN70 revealed structural features characteristic of transport pro teins, and was found to share similarity with the oxalate/formate exch ange protein of Oxalobacter formigenes. Therefore, we postulate that t he L. japonicus LjNOD70 gene family encodes nodule-specific transport proteins, which may have evolved as a result of exon-intron shuffling.