The calcium transporter ANNEXIN1 mediates cold-induced calcium signaling and freezing tolerance in plants

The transient elevation of cytosolic free calcium concentration ([Ca(2+)](cyt)) induced by cold stress is a well‐established phenomenon; however, the underlying mechanism remains elusive. Here, we report that the Ca(2+)‐permeable transporter ANNEXIN1 (AtANN1) mediates cold‐triggered Ca(2+) influx and freezing tolerance in Arabidopsis thaliana. The loss of function of AtANN1 substantially impaired freezing tolerance, reducing the cold‐induced [Ca(2+)](cyt) increase and upregulation of the cold‐responsive CBF and COR genes. Further analysis showed that the OST1/SnRK2.6 kinase interacted with and phosphorylated AtANN1, which consequently enhanced its Ca(2+) transport activity, thereby potentiating Ca(2+) signaling. Consistent with these results and freezing sensitivity of ost1 mutants, the cold‐induced [Ca(2+)](cyt) elevation in the ost1‐3 mutant was reduced. Genetic analysis indicated that AtANN1 acts downstream of OST1 in responses to cold stress. Our data thus uncover a cascade linking OST1‐AtANN1 to cold‐induced Ca(2+) signal generation, which activates the cold response and consequently enhances freezing tolerance in Arabidopsis.