Get the message: Uncovering cellular signalling processes in marine phytoplankton.

Marine phytoplankton live in diverse and constantly changing environments. They must be able to sense and perceive changes in abiotic and biotic stimuli to exploit the transient availability of resources or avoid damaging stressors. Cell signalling processes to detect their environment are therefore critical to the ecological success of these primary producers, but until recently the cellular mechanisms of signal transduction in marine phytoplankton have remained largely uncharacterised. Advances in genomic and transgenic approaches have greatly enabled our ability to study complex signalling processes, most notably in the diatoms. In addition, sensitive analytical techniques have allowed researchers to begin to unravel the complex composition of extracellular infochemicals emitted and sensed by marine algae. This review will examine these recent advances, focusing primarily on sensory perception and signal transduction in diatoms. We will examine the role of second messengers such as calcium, reactive oxygen species and cyclic nucleotides in sensing a range of abiotic stimuli including light, temperature, nutrients and salinity. We will also review progress made in identifying signalling mechanisms underlying biotic interactions between diatoms and other organisms such as grazers, competitors and microbial symbionts. Whilst diatoms possess many of the conserved cell signalling mechanisms found in other eukaryotes, they also possess unique aspects of cell physiology that underlie their ability to compete in specific aquatic environments. Many aspects of cell signalling in diatoms and other phytoplankton remain to be examined and we identify several important areas for future research.