Genetically engineered plant endophytes broaden effector-triggered immunity.

Plants utilize nucleotide-binding leucine-rich repeat (NLR) receptors to detect pathogen effectors and initiate a potent immune response called effector-triggered immunity (ETI). However, this defense relies on the presence of recognizable effectors in pathogens, which is often unpredictable during natural infections. To address this, we engineer plant endophytes, termed Sentinels, to heterologously express effectors that are recognized by the host's corresponding NLR. Using an OxyR regulatory circuit, effector expression is activated by reactive oxygen species-a common signal during pathogen infection. This circuit enables ETI activation against pathogens without recognizable effectors. Colonization by the sentinel bacterium slightly alters microbial abundance but maintains overall microbiota diversity and normal plant growth. We demonstrate the strategy's versatility by testing distinct effector-NLR recognition pairs in various plants against a range of pathogens. This strategy exploits the microbiota-host-pathogen interaction network to rapidly engineer a spectrum-expanded ETI, complementing synthetic microbial consortia for plant defense.