CIPK-B is essential for salt stress signalling in Marchantia polymorpha

Calcium signalling is central to many plant processes, with families of calcium decoder proteins having expanded across the green lineage and redundancy existing between decoders. The liverwort Marchantia polymorpha has fast become a new model plant, but the calcium decoders that exist in this species remain unclear. We performed phylogenetic analyses to identify the calcineurin B-like (CBL) and CBL-interacting protein kinase (CIPK) network of M. polymorpha. We analysed CBL-CIPK expression during salt stress, and determined protein-protein interactions using yeast two-hybrid and bimolecular fluorescence complementation. We also created genetic knockouts using CRISPR/Cas9. We confirm that M. polymorpha has two CIPKs and three CBLs. Both CIPKs and one CBL show pronounced salt-responsive transcriptional changes. All M. polymorpha CBL-CIPKs interact with each other in planta. Knocking out CIPK-B causes increased sensitivity to salt, suggesting that this CIPK is involved in salt signalling. We have identified CBL-CIPKs that form part of a salt tolerance pathway in M. polymorpha. Phylogeny and interaction studies imply that these CBL-CIPKs form an evolutionarily conserved salt overly sensitive pathway. Hence, salt responses may be some of the early functions of CBL-CIPK networks and increased abiotic stress tolerance required for land plant emergence.

Automated summary

In this study, we identified the CBL-CIPK network in the liverwort Marchantia polymorpha using phylogenetic analyses. We found that M. polymorpha has two CIPKs and three CBLs, and their expression is significantly changed under salt stress. All CBL-CIPK proteins in M. polymorpha interact with each other in planta. Knocking out CIPK-B increased sensitivity to salt, suggesting its involvement in salt signaling. These findings reveal a salt tolerance pathway mediated by CBL-CIPKs in M. polymorpha and suggest that salt responses may be an early function of CBL-CIPK networks, contributing to the emergence of land plants.