Calcium (Ca2+) is an important secondary messenger necessary for the propagation of intracellular signalling cascades in response to various stimuli. In plants, changes in cytosolic Ca2+ are sensed by calcium-sensor proteins such as calcium-dependent protein kinases (CDPKs). This unique protein family acts as Ca2+-sensor/kinase effectors capable of both sensing and transducing Ca2+ signals. Arabidopsis thaliana CPK28 is a negative regulator of immunity that prevents damaging overactivation of immune signals. Highly conserved CPK28 orthologs have been identified in all land plants including one of the first to colonize, Marchantia polymorpha (MpCPK28), and a representative of the transition to vascular plants, Selaginella moellendorffii (SmCPK28 and SmCPK16). Based on the conservation of CPK28 orthologs across evolutionary time, I aimed to investigate the level of functional conservation in extant species. MpCPK28, SmCPK16, and SmCPK28 were cloned and transiently expressed in Nicotiana benthamiana in order to determine subcellular localization. Transgenic Arabidopsis plants expressing MpCPK28, SmCPK16, and SmCPK28 were generated in a CPK28 loss-of-function background (cpk28-1) to determine if they could complement the high immune output of cpk28-1 plants, pointing to functional conservation. I further aimed to investigate the kinase activity and calcium- dependency of MpCPK28 to determine if the kinase is regulated similarly to AtCPK28. Preliminary analysis of MpCPK28 suggests the kinase localizes to both the plasma membrane and nucleus, unlike AtCPK28 which localizes exclusively to the plasma membrane. The nuclear localization of MpCPK28 could provide evidence for a unique function for this CPK28 ortholog. Genetic analysis of transgenic Arabidopsis lines expressing M. polymorpha and S. moellendorffii CPK28 orthologs will provide evidence for conservation of immune function which could point towards a core immune pathway that has been evolutionarily maintained.