Abstract: The brown planthopper (Nilaparvata lugens St?l, BPH) is a major rice pest that feeds on sieve tubes, where plants respond by depositing callose to restrict phloem sap ingestion. However, the molecular basis of how rice stabilizes callose at plasmodesmata and how BPH overcomes this defense remains poorly understood. Here, we identify OsPDCB1, a plasmodesmal callose-binding protein that positively regulates BPH resistance by anchoring callose through its X8 domain. Loss- and gain-of-function analyses demonstrate that OsPDCB1 is essential for callose accumulation and effective phloem defense. We further identified NlVRSP1, a BPH salivary effector that is highly conserved across rice planthopper species. This effector directly interacts with OsPDCB1 and disrupts its callose-binding activity, revealing a previously uncharacterized effector?host interaction module at the plasmodesmal interface. Importantly, haplotype analysis uncovered a resistance-associated allele (OsPDCB1^Hap1), enriched in Indica rice, which enhances resistance when introgressed into susceptible Japonica backgrounds. Collectively, these findings identify OsPDCB1 as a key mediator of callose-based defense and a promising genetic target for breeding BPH-resistant rice cultivars, while providing mechanistic insight into how insect effectors subvert plasmodesmal immunity.

Key words: callose, OsPDCB1, plasmodesma, brown planthopper, salivary protein