The triose phosphate/phosphate translocator exports photosynthetic glyceraldehyde 3-phosphate from chloroplasts to trigger antimicrobial immunity in plants.

Chloroplasts play a crucial role in plant immunity against invading microbes. However, it remains poorly understood whether photosynthetic metabolites from chloroplasts participate directly in host defenses. Here, we uncovered Arabidopsis thalinana triose phosphate/phosphate translocator (AtTPT), a known translocator for chloroplast inner membrane, plays an indispensable role in suppressing virus infection and evoking defense responses. Interestingly, overexpression of AtTPT impairs virus accumulation in plants, while loss-of-function tpt3 mutants exhibit an increased viral load. The antiviral activity of AtTPT requires its phosphate transport capacity, implying that it actually functions through its metabolite(s). To this end, we found that glyceraldehyde 3-phosphate (GAP), one of AtTPT's translocated metabolites, can drastically enhance expression of defense-related genes and prominently induce defense signaling pathways. More excitingly, AtTPT or GAP robustly restricts the proliferation of multiple types of phytopathogens. Collectively, we propose that AtTPT exports GAP to mediate broad-spectrum resistance to pathogens, which provides new insights into the mechanism underlying the chloroplast-mediated immunity by a photosynthetic metabolite.