Multitasking mediators: revealing the secret jobs of plant metacaspases

As sessile organisms, plants must constantly survey their surroundings and make appropriate responses in their metabolism or development. Numerous receptors and kinases, as well as phytocytokines that play key roles in signal transduction for a multitude of cues, have been revealed in the past 2 decades. However, the mechanisms coordinating these responses remain poorly understood. Recently, the conserved plant metacaspase family emerged as a versatile switch that plays multiple roles, from early signal perception to downstream propagation, by proteolysis of propeptides or other signaling proteins to mediate their conversion to activated forms. In addition, evidence for proteolysis-independent functions of plant metacaspases has also emerged. In this feature review, we summarize advances in plant metacaspase functions and consider approaches to unravel their complex impacts.