Jcb_201605110 1..14

In eukaryotes, regulated cell death (RCD) is an active mechanism essential for development, immune responses, and many pathophysiological processes (Hakem et al., 1998; Yoshida et al., 1998; Lindsten et al., 2000; Van Hautegem et al., 2015). In animals, cell death was traditionally classified into three categories, based on the morphological features exhibited by cells during the death process, as apoptotic, autophagic, or necrotic (Kroemer et al., 2009). In recent years, this tripartite classification scheme has been challenged by the discovery of new forms of cell death that differ from these canonical categories, such as pyroptosis and necroptosis (Bergsbaken et al., 2009; Christofferson and Yuan, 2010). Most recently, a new form of cell death that was shown to be morphologically, biochemically, and genetically distinct from apoptosis, necrosis, and autophagy was described in cancer cells, in kidney tissue, and in the nervous system. This type of cell death was named ferroptosis, as it is dependent on intracellular iron, which is required for the accumulation of toxic lipid reactive oxygen species (ROS; Yang and Stockwell, 2008; Dixon et al., 2012; Friedmann Angeli et al., 2014; Linkermann et al., 2014; Skouta et al., 2014; Yang et al., 2014). A defining feature of ferroptosis is that it can be prevented by treatment of cells with iron-chelating agents, such as deferoxamine or ciclopirox olamine (CPX), or with lipophilic antioxidants, such as ferrostatin 1 (Fer-1) or vitamin E (Yagoda et al., 2007; Yang and Stockwell, 2008; Dixon et al., 2012; Skouta et al., 2014; Yang et al., 2014). Although the specific role of iron in ferroptosis remains unclear, it is unlikely to be explained by a simple increase in iron-catalyzed ROS production (i.e., Fenton chemistry), as cell death induced by peroxide is in many aspects different from ferroptosis (Dixon et al., 2012). In plants, RCD mechanisms play critical roles during several developmental processes, such as megasporogenesis, fertilization, embryogenesis, development of tracheary elements, and regulation of leaf shape (Gunawardena et al., 2004; Drews and Koltunow, 2011; Bollhöner et al., 2012; Choi, 2013). Additionally, abiotic stresses, such as salt stress, drought, and nutrient starvation, are able to induce plant cell death (Liu et al., 2009). Plant cells do not undergo apoptosis as defined by classic In plants, regulated cell death (RCD) plays critical roles during development and is essential for plant-specific responses to abiotic and biotic stresses. Ferroptosis is an iron-dependent, oxidative, nonapoptotic form of cell death recently described in animal cells. In animal cells, this process can be triggered by depletion of glutathione (GSH) and accumulation of lipid reactive oxygen species (ROS). We investigated whether a similar process could be relevant to cell death in plants. Remarkably, heat shock (HS)–induced RCD, but not reproductive or vascular development, was found to involve a ferroptosis-like cell death process. In root cells, HS triggered an iron-dependent cell death pathway that was characterized by depletion of GSH and ascorbic acid and accumulation of cytosolic and lipid ROS. These results suggest a physiological role for this lethal pathway in response to heat stress in Arabidopsis thaliana. The similarity of ferroptosis in animal cells and ferroptosis-like death in plants suggests that oxidative, iron-dependent cell death programs may be evolutionarily ancient. Heat stress induces ferroptosis-like cell death in plants