The asparagine synthetase gene VfAS1 is strongly expressed in the nitrogen-fixing zone of broad bean (Vicia faba L.) root nodules

A full-length transcript sequence encoding the broad bean (Vicia faba L.) asparagine synthetase (AS) VfAS1 was isolated from a nodule cDNA library. Sequence homologies indicated that VfAS1 belonged to the glutamine-dependent type of AS enzymes. The corresponding gene was highly expressed in root nodules and at a three-fold lower level in uninfected roots. Additionally, traces of VfAS1 transcripts were detected in epicotyl and stem tissues. Tissue-print hybridizations revealed that the VfAS1 gene was strongly expressed in the nitrogen-fixing zone III of root nodules, VfAS1 transcripts were absent from the meristem, the prefixing zone II as well as from peripheral nodule tissues.