The NLR splice variant BNT1.1 contributes to vascular defense responses affecting callose accumulation and Myzus persicae feeding in Arabidopsis

Aphids are phloem-feeding insects that probe through successive plant cell layers before establishing sustained feeding in sieve elements. During this process, they secrete salivary effectors that can modulate plant immune responses to facilitate access to vascular tissues. Although nucleotide-binding leucine-rich repeat receptors (NLRs) are central components of plant immunity against microbial pathogens, their role in plant-aphid interactions remains poorly understood. Here, we investigated the Arabidopsis TIR-type NLR BURNOUT1 (BNT1), which produces two transcriptional isoforms with distinct tissue distributions. Previous work showed that the plastid-localized isoform BNT1.2 accumulates mainly in epidermal tissues and contributes to antibacterial immunity, whereas the function of the vascular-enriched isoform BNT1.1 remains unknown. During infestation by the green peach aphid ( Myzus persicae ), BNT1 expression was transiently induced, with BNT1.1 accumulating markedly in vascular tissues while BNT1.2 remained enriched in epidermal fractions. Moreover, loss-of-function bnt1 mutants displayed increased aphid reproduction and prolonged phloem sap ingestion, as measured by electrical penetration graph recordings. These plants also showed reduced callose deposition in vascular tissues and lower expression of the phloem-associated callose synthase gene CALS7 . Restoring BNT1.1 expression in the bnt1 background increased callose accumulation at aphid feeding sites and rescued the feeding phenotype. Overall, our results indicate that BNT1 plays a role in vascular defense responses that limit prolonged phloem feeding by aphids. Together, our findings reveal that alternative transcription of immune receptors contributes to spatially resolved defense responses in plants. This work highlights a mechanism linking molecular diversification to cell-type-specific immunity and provides new insight into how plants coordinate defense strategies against phloem-feeding insects.