A triose phosphate/phosphate translocator triggers antimicrobial immunity by exporting glyceraldehyde 3-phosphate from chloroplasts.

Chloroplasts play a crucial role in plant immunity against invading microbes. However, whether photosynthetic metabolites from chloroplasts participate directly in host defenses remains poorly understood. Here, we uncovered that an Arabidopsis thaliana triose phosphate/phosphate translocator (TPT) in the inner membrane of the chloroplast envelope suppresses viral infection and evokes defense responses. AtTPT overexpression impairs virus accumulation in plants, and loss-of-function tpt-3 mutants exhibit an increased viral load. The antiviral activity of AtTPT requires its metabolite transport capacity, implying that it indeed functions through its metabolite(s). To this end, we found that glyceraldehyde 3-phosphate (GAP), one the metabolites translocated by AtTPT, drastically enhances the expression of defense-related genes and induces defense signaling pathways. Moreover, AtTPT or GAP robustly impairs the proliferation of diverse phytopathogens. Therefore, we propose that AtTPT exports GAP to mediate broad-spectrum pathogen resistance, which provides insights into the mechanisms underlying chloroplast-mediated immunity induced by a photosynthetic metabolite.