A nonsymbiotic hemoglobin gene from maize, ZmHb, is involved in response to submergence, high-salt and osmotic stresses

Nonsymbiotic hemoglobins (nsHbs) are involved in a variety of cellular processes in plants. Previous studies on nsHbs suggest their function in response to hypoxic stress. Here, we report on the cloning and characterization of a maize nsHb gene (ZmHb) and its 5' flanking sequences from maize inbred Zong31. Southern analysis suggests that the ZmHb gene is present in two copies or a low number of copies in the maize genome. Expression analysis by Northern blot shows that ZmHb mRNA levels in maize seedlings are induced by high-salt and osmotic stresses in addition to hypoxic stress. Promoter-GUS analysis has revealed that ZmHb promoter-driven GUS activity is localized to root tips and vascular tissues. Moreover, it is under similar patterns of regulation based on mRNA levels under the above environmental stress conditions. Ectopic expression of ZmHb in transgenic tobacco has enhanced plant tolerance to submergence, salinity and osmotic stresses. These results indicate that expression of ZmHb at transcript levels is regulated under multiple stress conditions in maize roots, suggesting an important role of ZmHb in plant stress tolerance.