Identification of Nramp gene family in Hydrangea macrophylla and characterization of HmNramp5 under aluminum stress condition.

Aluminum toxicity severely limits plant growth in acidic soil. The Nramps play crucial role in transporting mineral elements in plants, but their role in hydrangea remains unexplored. The six HmNramp genes identified from hydrangea genome were found to be preferentially expressed in roots and flowers under aluminum stress, implying their crucial roles in aluminum tolerance and transport. Under aluminum stress, the HmNramp5 expression levels were 0.43, 0.19 and 0.73-fold higher than control in flower, leaf and roots, respectively. The overexpression (OE) of HmNramp5 showed higher resistance to aluminum and manganese but increased sensitivity to cadmium in yeast. Furthermore, the lower death rate (42 %) of leaf discs infiltrated with HmNramp5-OE under aluminum stress was observed as compared to empty vector. Aluminum stress significantly increased the contents of hydrogen peroxide, superoxide anion radical, and malonaldehyde in control samples, which elevated the harmful oxidation effect on plant cells. However, these contents were significantly reduced by HmNramp5-OE. Additionally, the levels of superoxide dismutase and peroxidase were significantly higher in HmNramp5-OE samples compared to the empty vector, indicating that HmNramp5 gene may stimulate their activities. These findings provide valuable insights into the functions of HmNramps in aluminum tolerance and transport in hydrangea.