Discovery of cadmium-tolerant biomacromolecule (StCAX1/4 transportproteins) in potato and its potential regulatory relationship with WRKY transcription factors

The cation/H+ exchanger (CAX) involved in Ca2+, Mg2+ and Mn2+ transport is a special class of vacuolar transporters that play an important role in maintaining ion homeostasis in plant cells. However, it has been rarely reported whether CAX proteins have unique tolerance to cadmium stress. In our research, the cadmium-resistant potato variety "Yunshu 505" was taken as the object, through biological etc. methods, explored 1: response mode of StCAXs to cadmium stress; 2: the evolutionary characteristics and Cd ion binding sites of StCAXs; and 3: possible upstream regulatory pathways of StCAXs. The results showed that cadmium stress significantly induced the expression of StCAX1/4, and there were specific mutations in the evolution process, thus the possible main binding site of Cd ion (EDEE/DH/GxxxxxS/EEEE) was speculated. StCAX1/4 interacts with several proteins, and be regulated by transcription factors, especially the WRKY6. This synergistic regulation through WRKY6 may be an important pathway through which StCAX1/4 imparts high cadmium tolerance to potato. These results provide certain support for understanding the binding sites and specific evolutionary mechanisms of key amino acid residues of cadmium ion in StCAXs, also provide new clues for the identification and regulatory model of potato CAX key positive stress-responsive proteins under cadmium stress.