ORGANIZATION AND EXPRESSION OF GENES IN THE GENOMIC REGION SURROUNDING THE GLUTAMINE-SYNTHETASE GENE GLN1 FROM LOTUS-JAPONICUS

The diploid Lotus japonicus was previously suggested as a model for th e legume plant family. We present here the nucleotide sequence and the derived gene organization of a small part of the genome in this model plant. Two functional genes with the same transcriptional orientation were identified within the 23 326-bp genomic region analysed. The LjG ln1 gene encodes a cytosolic glutamine synthetase and the LjKrm (Kines in repeat motif) gene encodes a polypeptide with similarity to a repea ted motif present in the microtubule-associated kinesin light chain pr otein. Transcripts of the glutamine synthetase gene are found primaril y in roots and root nodules, while transcripts of the Krm gene are fou nd in roots, root nodules and leaves, In the region between Gln1 and K rm, the presence of a third gene, Pge1, was suggested by analysis with the Grail exon recognition program. Upstream of the Gln1 gene a segme nt carrying two apparently non-functional, fragmented copia-like retro elements, dRtp1 and dRtp2, was identified. Sequence similarity to reve rse transcriptase- and RNaseH-coding regions defined the defective ret roelements dRtp1 and dRtp2 within this segment. Terminal repeats were not found but three different sets of short direct repeats are located adjacent to the dRtp1 element. The three genes and the incomplete ret roelements occupy most of the analysed DNA, leaving approximately one- fifth of the chromosome fragment without recognisable genome constitue nts.