Overexpression of GmCSY3 Enhances Soybean Tolerance to Excess Iron and Aluminum

Background: Plant citrate synthase (CSY) is involved in the iron deficiency (−Fe) response and aluminum (Al) detoxification. However, knowledge of CSY function in responding to excess iron (+Fe) or Al stress (+Al) is still limited. Methods: The CDS and promoter of GmCSY3 were isolated from soybean and bioinformatically analyzed. The GmCSY3 expression was detected by qRT-PCR and GUS assay. The growth of GmCSY3 recombinant yeast under +Fe or +Al was detected. The phenotype, CSY activity, citric acid concentration, chlorophyll content, MDA, H2O2, O2− contents, GST, CAT, SOD, and POD activities were examined in GmCSY3 overexpressed and RNAi-suppressed soybean chimeras under +Fe or +Al. Perls and Hematoxylin stained the roots, and the FCR activity was determined. Results: GmCSY3 was induced by +Fe or +Al, but not by −Fe. GmCSY3 enhanced yeast’s acid production and resistance to +Fe or +Al. GmCSY3 overexpression in soybean significantly enhanced CSY activity, promoted growth, alleviated oxidative damage caused by +Fe or +Al, with less free Fe3+ and Al3+, and reduced FCR activity, while GmCSY3 RNAi-suppressed showed the opposite effect. Conclusions: GmCSY3 promotes the process of citrate synthesis, chelates Fe3+ and Al3+, alleviates oxidative damage caused by +Fe or +Al, and modulates iron absorption in plants.