Channels of Evolution: Unveiling Evolutionary Patterns in Diatom Ca²⁺ Signalling

Diatoms are important primary producers in marine and freshwater environments, but little is known about the signalling mechanisms they use to detect changes in their environment. All eukaryotic organisms use Ca²⁺ signalling to perceive and respond to environmental stimuli, employing a range of Ca²⁺-permeable ion channels to facilitate the movement of Ca²⁺ across cellular membranes. We investigated the distribution of different families of Ca²⁺ channels in diatom genomes, with comparison to other members of the stramenopile lineage. The four-domain voltage-gated Ca²⁺ channels (Ca_v) are present in some centric diatoms but almost completely absent in pennate diatoms, whereas single-domain voltage-gated EukCatA channels were found in all diatoms. Glutamate receptors (GLRs) and pentameric ligand-gated ion channels (pLGICs) also appear to have been lost in several pennate species. Transient receptor potential (TRP) channels are present in all diatoms, but have not undergone the significant expansion seen in brown algae. All diatom species analysed lacked the mitochondrial uniporter (MCU), a highly conserved channel type found in many eukaryotes, including several stramenopile lineages. These results highlight the unique Ca²⁺-signalling toolkit of diatoms and indicate that evolutionary gains or losses of different Ca²⁺ channels may contribute to differences in cellular-signalling mechanisms between species.