Interactions between hydrogen sulphide and nitric oxide regulate two soybean citrate transporters during the alleviation of aluminium toxicity

Hydrogen sulphide (H₂S) is emerging as an important signalling molecule involved in plant resistance to various stresses. However, the underlying mechanism of H₂S in aluminium (Al) resistance and the crosstalk between H₂S and nitric oxide (NO) in Al stress signalling remain elusive. Citrate secretion is a wide‐spread strategy for plants against Al toxicity. Here, two citrate transporter genes, GmMATE13 and GmMATE47, were identified and characterized in soybean. Functional analysis in Xenopus oocytes and transgenic Arabidopsis showed that GmMATE13 and GmMATE47 mediated citrate exudation and enhanced Al resistance. Al treatment triggered H₂S generation and citrate exudation in soybean roots. Pretreatment with an H₂S donor significantly elevated Al‐induced citrate exudation, reduced Al accumulation in root tips, and alleviated Al‐induced inhibition of root elongation, whereas application of an H₂S scavenger elicited the opposite effect. Furthermore, H₂S and NO mediated Al‐induced GmMATE expression and plasma membrane (PM) H⁺‐ATPase activity and expression. Further investigation showed that NO induced H₂S production by regulating the key enzymes involved in biosynthesis and degradation of H₂S. These findings indicate that H₂S acts downstream of NO in mediating Al‐induced citrate secretion through the upregulation of PM H⁺‐ATPase‐coupled citrate transporter cotransport systems, thereby conferring plant resistance to Al toxicity.