Genome wide analysis of HMA gene family in Hydrangea macrophylla and characterization of HmHMA2 in response to aluminum stress.

Aluminum toxicity poses a significant threat to plant growth, especially in acidic soils. Heavy metal ATPases (HMAs) are crucial for transporting heavy metal ions across plant cell membranes, yet their role in Al ³⁺ transport remains unexplored. This study identified eight HmHMA genes in the genome of Hydrangea macrophylla, categorizing them into two major clades based on phylogenetic relationships. These genes were found unevenly distributed across six chromosomes. Detailed analysis of their physicochemical properties, collinearity, and gene structure was conducted. RNA-seq and qRT-PCR analyses revealed that specific HmHMA genes, notably HmHMA2, were predominantly expressed in roots and flowers under Al ³⁺ stress, indicating their potential role in Al ³⁺ tolerance. HmHMA2 showed significant expression in roots, especially under Al ³⁺ stress conditions, and when expressed in yeast cells, it conferred resistance to aluminum and zinc but increased sensitivity to cadmium. Overexpression of HmHMA2 in hydrangea leaf discs significantly improved Al ³⁺ tolerance, reduced oxidative stress markers like hydrogen peroxide and malondialdehyde, and enhanced antioxidant enzyme activity such as SOD, POD and CAT compared to controls. These findings shed lights on the potential role of HmHMAs in Al transport and tolerance in H. macrophylla.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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