Transcellular regulation of ETI-induced cell death.

To address the persistent challenge of cell death spread and limitation during effector-triggered immunity (ETI), we propose a 'concentric circle' model. This model outlines a regulatory framework, integrating multiple cells and diverse signaling molecules, including salicylic acid (SA), jasmonic acid (JA), and Ca²⁺. By accounting for the varying concentrations and spatiotemporal distributions of these molecules, our model aims for precision in immune defense and regulated cell death. To validate this model, a pathosystem-triggering ETI without pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) is required. Here, we review potential ETI elicitors, including victorin, thaxtomin A, and second messengers. We anticipate that future discovery of 'pure' ETI-triggering effectors will provide deeper insights into the transcellular regulation of immune response in plants.