A single hemoglobin gene in Myrica gale retains both symbiotic and non-symbiotic specificity.

Here, a hemoglobin gene from the nitrogen-fixing actinorhizal plant Myrica gale was isolated, cloned and sequenced. The gene (MgHb) was a class I hemoglobin with strong sequence homology to non-symbiotic hemoglobin genes. MgHb is highly expressed in symbiotic root nodules, but transcripts and protein were also detected in leaves of M. gale. In Arabidopsis thaliana the MgHb promoter, linked to a beta-glucuronidase coding region, directed expression in the vascular tissue, in shoot meristem and at root branch point--a pattern very similar to the combined expression pattern of the two non-symbiotic A. thaliana hemoglobin promoters AHb1 and AHb2. The results points to a symbiotic as well as a non-symbiotic specificity of MgHb similar to a hemoglobin gene identified in Parasponia andersonii, but different from the situation in Casuarina glauca--a close actinorhizal relative of M. gale.