<p>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.</p>