Synthetic fluorescent probes to apprehend calcium signalling in lipid droplet accumulation in microalgae: An updated review

Lipid bodies are dynamic organelles of photosynthetic microalgae that can be used as the third generation resources for biofuel production. Biosynthesis of lipids can be influenced by different signalling processes. Visualisation of these processes can provide useful information about the fate and associated roles of lipid molecules in different biological systems. In photosynthetic organisms, however, studies of calcium ediated lipid biosynthesis is bottlenecked due to the limitation of proper and efficient technologies, which also include visualisation techniques. Currently, most studies to visualise lipid droplets in vivo have used traditional dyes, and proper visualisation of lipid drops is hindered by dye-specific limitations. This hurdle could be overcome by using recently developed aggregation-induced emission biooprobes. This review reveals current knowledge gaps in the studies of lipid drops and calcium ions in microalgae, as calcium signaling is important secondary messenger to detect a wide variety of environmental stimuli in plant and animal cells. To obtain insight into the mechanisms of these processes, the merits and demerits of currently available visualisation techniques for lipid drops and calcium are also detailed. Finally, opportunities and possibilities are proposed to recommend further improvement of techniques for detecting the role of calcium during lipid formation in microalgae for biofuel production.