Calcium signaling in hypoxic response.

Plants can experience a lack of oxygen due to environmental conditions, such as flooding events or intense microbial blooms in the soil, and from their own metabolic activities. The associated limit on aerobic respiration can be fatal. Therefore, plants have evolved sensing systems that monitor oxygen levels and trigger a suite of metabolic, physiologic, and developmental responses to endure, or potentially escape, these oxygen-limiting conditions. Low oxygen stress has long been known to trigger changes in cytosolic Ca2+ levels in plants, and recent work has seen some major steps forward in characterizing these events as part of a Ca2+-based signaling system through (1) defining how hypoxia may trigger and then shape the dynamics of these Ca2+ signals, and (2) identifying a host of the downstream elements that allow Ca2+ to regulate a wide-ranging network of hypoxia responses. Calcium transporters such as the CAX family of Ca2+/H+ antiporters at the tonoplast have emerged as important components of the system that forms hypoxia-related Ca2+ signals. Downstream lies a web of Ca2+-responsive proteins such as the calmodulin like proteins, Ca2+-dependent kinases, and the calcineurin-B like proteins along with their interacting kinases. A host of other regulators such as reactive oxygen species and lipid-mediated signals then act in parallel to the Ca2+-dependent events to closely control and coordinate the myriad responses that characterize the plant's low oxygen response.