Organ regulated expression of Parasponia andersonii haemoglobin gene in transgenic tobacco plants.

Plant haemoglobin genes are known to occur in legume and non-legume families and in both nodulating (e.g., Parasponia andersonii) and non-nodulating species (e.g., Trema tomentosa). Their presence in non-nondulating plants raises the possibility that haemoglobins might serve a function in non-symbiotic tissues distinct from their role in the nitrogen-fixing root nodules induced by micro-organisms. We report here that a P. andersonii haemoglobin promoter can regulate expression of either the P. andersonii haemoglobin gene, or a hybrid construct with the bacterial chloramphenicol acetyltransferase gene (cat), in the non-symbiotic plant, Nicotiana tabacum. Expression is predominantly in the roots, implying that haemoglobins might have a function in roots of non-nodulated plants. We have also observed a low level of haemoglobin protein in non-nodulated P. andersonii roots, but not leaves, supporting this assertion. The expression in transgenic plants will allow further characterization of the promoter sequences essential for the organ-specific expression of haemoglobins in non-symbiotic tissues.