Functional identification of protein kinase MhSnRK2.4 involved in Fe-deficiency stress in Malus halliana Koehne

SnRK (sucrose non-fermenting protein kinase family), a class of serine/threonine (Ser/Thr) protein kinases, is widely distributed in plants and is divided into three subfamilies: SnRK1, SnRK2, and SnRK3. The SnRK2 family, in particular, plays a significant role in osmotic stress resistance and ABA signaling pathways. However, research on the relationship between the SnRK2 gene and iron (Fe) deficiency in apples is limited. Studies have shown that the SnRK2.4 gene exhibited higher regulation of expression under Fe-deficient conditions compared to other genes. Yet, the mode of action of this gene in regulating Fe-deficiency stress remains unexplained. Therefore, the MhSnRK2.4 gene (Genbank ID:103411041) was cloned from Malus halliana in the present study. It was observed that transgenic Arabidopsis plants exhibited more robust growth and reduced chlorosis under Fe-deficiency stress when compared to the wild-type control. The overexpressed apple calli also exhibited enhanced growth Fe-deficiency stress. In addition, measurements of physiological indices showed that overexpression of the MhSnRK2.4 gene increased the tolerance of Arabidopsis thaliana to Fe-deficiency damage by promoting chlorophyll synthesis, Fe-deficiency damage by promoting chlorophyll synthesis, increasing the activity of antioxidant end enzymes, and promoting Fe reduction, and apple calli to Fe-deficiency damage by decreasing pH, increasing the activity of antioxidant end enzymes, and promoting Fe uptake. In conclusion, the overexpression of the MhSnRK2.4 gene enhanced the resistance to Fe-deficiency stress in Arabidopsis and apple calli, increasing antioxidant enzyme activity, and promoting Fe reduction.