Unraveling plant immunity: from pathogen perception to resistance engineering

Unlike animals, which rely on circulatory systems and mobile immune cells, each plant cell must autonomously detect and respond to pathogenic threats. Plant immunity operates through two major layers: pattern-triggered immunity (PTI), initiated by cell-surface pattern recognition receptors (PRRs), and effector-triggered immunity (ETI), primarily mediated by intracellular nucleotide-binding leucine-rich repeat (NLR) receptors. Recent advances have substantially enhanced our understanding of PTI and ETI signaling. Notably, some NLRs following activation by specific recognition of pathogen effectors form higher-order oligomeric complexes termed resistosomes that act as Ca²⁺-permeable channels to trigger immune signaling. Increasing evidence points to extensive crosstalk and mutual potentiation between PTI and ETI, with Ca²⁺ functioning as a pivotal second messenger in both pathways. Elucidating the molecular basis of these pathways, combined with emerging tools like CRISPR/Cas9, offers new strategies for engineering durable disease resistance in crops. This review highlights current insights into PTI and ETI, with an emphasis on the central role of Ca²⁺ signaling and key challenges in engineering NLR receptors.