An Ocean of Signals: Intracellular and Extracellular Signaling in Diatoms

Diatoms are frequently exposed to diverse biotic and abiotic stressors, and they rely on sophisticated sensing mechanisms to perceive and respond accordingly to fluctuations in their environment. In order to convert diverse environmental cues into activation of specific signal transduction pathways, diatoms utilize an array of second messengers such as reactive oxygen species (ROS), nitric oxide (NO), calcium (Ca2+), and cyclic nucleotides (cAMP and cGMP). Specificity in signal transduction is achieved by precise spatiotemporal control of the level of second messengers, the specific combination of these molecules, and their available cellular targets. In addition to second messengers, diatoms utilize other chemical cues that are exuded by conspecifics and other organisms in their microenvironment. These molecules, named infochemicals, convey an essential information on the producer physiological state, and serve as a chemical language that mediates marine microbial interactions. These infochemicals have specific bioactivities, and some are toxic to competitors, grazers, or pathogens. The outcomes of this chemical communication highly depend on the context, and the same signal may lead to different cell fates. In some cases, chemical cues can even initiate a programmed cell death (PCD) cascade, which was suggested to contribute to the high turnover of phytoplankton and to be involved in bloom demise. In this chapter, we discuss the current knowledge regarding diatom extracellular and intracellular signaling, mainly during biotic interactions. In addition, we discuss how cellular processes that occur at the single-cell level may alter population dynamics and even large-scale biogeochemical processes. Finally, we propose future research directions that will shed light on the ecological importance of chemical communication in diatoms.