The role of plant metacaspases in cell death and survival.

In plants, metacaspases-cysteine proteases-have gained attention for their roles in programmed cell death (PCD). However, to date, their proteolytic activity has not been established as a direct executioner of PCD, analogous to caspases in animals. In this regard, the specific executioners of PCD remain to be identified in plants, leaving the process less well understood than in animals. More recently, metacaspases have also been recognized for their roles in cellular homeostasis. This perspective explores the pro-death and pro-survival roles of plant metacaspases in plant stress responses and development. Under abiotic stress conditions, such as heat, drought or high salinity, metacaspases help maintain protein homeostasis and mitigate damage by regulating processes like the unfolded protein response. In plant immunity, metacaspases have context-dependent pro-death or pro-survival roles. Pro-survival roles include cleavage and generation of immune peptides and regulating immune receptor stability as part of immunocondensates. They have also been shown to tightly regulate immunogenic cell death after pathogen attack, although their mode of action in this context remains elusive. Developmentally, metacaspases participate in key processes that involve PCD, like xylem differentiation and lateral root cap formation, where they help control cellular remodelling. Ultimately, metacaspases are emerging as multifunctional molecules crucial to cellular integrity, immunity, and development. Understanding the balance between cell death and survival pathways in plants is crucial, as it directly impacts crop resilience to environmental stresses and pathogens, ultimately influencing food security and our dependence on plant-based resources.