Visualizing Ca2+ signatures in plants

Ca2+ is a key player in an astonishing variety of plant signal transduction pathways where transient, spiking or oscillatory changes in cytosolic Ca2+ levels help to couple environmental or developmental cues to appropriate cellular responses. Understanding whether and how much Ca2+ signaling contributes to defining stimulus-response specificity has long been a challenge, but recent work has provided strong evidence that specific information can indeed be encoded in the spatiotemporal characteristics of Ca2+ signals. Identification of the Ca2+ binding proteins that transduce Ca2+ signals by regulating downstream effector proteins has revealed a complex network of Ca2+ sensor families, of which some members show distinct patterns of expression and subcellular localization. By utilizing genetically encoded fluorescent Ca2+ probes to monitor Ca2+ changes at high spatiotemporal resolution, it is now possible to explore whether such spatial heterogeneities in Ca2+ sensor distribution are coordinated with subcellular microdomains of Ca2+ signaling. Such visualization of Ca2+ signaling will also help to address which cellular compartments and transporters contribute to mobilizing and sequestering Ca2+ and thus define stimulus-specific Ca2+ signatures.

► Ca2+ signatures encode information that specify downstream responses. ► Genetically encoded fluorescent Ca2+ reporters have revealed spatially complex Ca2+ signatures in response to different environmental perturbations. ► Subcellular targeting of genetically encoded fluorescent Ca2+ reporters continues to pose technical challenges. ► Ca2+ imaging can be utilized to determine auxin transport kinetics in real time at cellular resolution.