CSLB4-mediated cell wall remodeling decouples phloem access from aphid performance in Arabidopsis thaliana

The plant cell wall (CW) is a key determinant of plant defense; however, the extent to which natural variation in CW architecture contributes to resistance against phloem-feeding insects remains unclear. Here, we combined genome-wide association studies (GWAS) with functional analyses to identify genetic determinants of resistance against the specialist aphid Brevicoryne brassicae in Arabidopsis thaliana. GWAS conducted on 200 natural accessions identified a single locus on chromosome 2 associated with aphid performance. Integration of haplotype and epidermis-specific expression data prioritized CSLB4, a member of the cellulose synthase-like B family. Loss-of-function cslb4 mutants showed reduced aphid offspring, indicating enhanced resistance to B. brassicae, whereas performance of the generalist aphid Myzus persicae was unaffected. Electrical penetration graph analyses revealed earlier phloem access on cslb4 mutants despite reduced performance, indicating a decoupling between phloem access and aphid success. Biochemical and immunolocalization analyses showed that CSLB4 disruption altered CW architecture, including increased xyloglucan epitope accessibility in mesophyll cell walls and reduced callose deposition upon aphid infestation. In addition, CSLB4 localized to Golgi-associated compartments, and in silico analyses are consistent with a role in non-cellulosic polysaccharide biosynthesis. Together, these findings identified CSLB4 as a modulator of CW architecture that uncouples phloem access from aphid performance. HighlightA GWAS identifies CSLB4 as a regulator of cell wall architecture that uncouples aphid-feeding from performance, revealing a new mechanism of plant resistance to specialist insects.