Medeiros, T. C. D.; Reato, S.; Li, X.; Garcia, B. M.; Rais, I.; Allmeroth, K.; Hartman, M.; Denzel, M.; Purrio, M.; Mesaros, A.; Leung, K.-y.; Greene, N.; Giavalisco, P.; Pernas, L.

As large consumers of cellular metabolites, mitochondria are positioned to compete with invading microbes for the nutrients they require to grow. Yet, little is known of whether cells weaponize mitochondrial metabolism during infection. We found that the transcription factor ATF4 activated a mitochondrial metabolic defense based on the essential B vitamin folate. During infection with the human parasite Toxoplasma gondii, ATF4 increased mitochondrial DNA (mtDNA) levels by driving the one-carbon (1C) metabolism processes that occur in mitochondria and use folate. The activation of ATF4 depended on host detection of parasite effector proteins, and restricted parasite growth by limiting its access to folate(s) required for dTMP synthesis. Impairing host mitochondrial 1C metabolism downstream of ATF4 promoted parasite growth, while forcing host dependence on mitochondrial 1C metabolism had the opposite effect. ATF4 activation also promoted a host-protective response in a mouse model of Toxoplasma infection. Thus, ATF4 rewires mitochondrial metabolism to activate a folate-based metabolic immunity against Toxoplasma. Our work paves the way for future studies exploring noncanonical defense strategies mediated by mitochondria and the role of folate metabolism during infectious disease.