Does climate shape plant immune gene repertoires? A phylogenetically controlled test across angiosperms

Background The number of immune receptor genes - cell-surface pattern recognition receptors (PRRs) and intracellular NLRs - varies by more than an order of magnitude across flowering plants, but the ecological and evolutionary correlates of this variation remain unclear. A widely held expectation is that plants in warmer, wetter, lower-latitude environments experience greater pathogen pressure and therefore maintain larger immune repertoires. Because immune gene counts and climatic niche are both inherited along the phylogeny, testing this expectation requires explicit phylogenetic correction. I related per-species counts of all 39 annotated immune receptor families to climate, geography, and functional traits across angiosperms, and tested whether ambient fungal pathogen exposure explains any residual association. Results Bivariate screening across 584 non-special-lifestyle species identified 56 of 702 climate-receptor correlations as significant, but all effect sizes were modest (|ρ| ≤ 0.24) and none survived phylogenetic generalised least squares (PGLS) correction. Among functional traits, eleven of 585 tests survived correction, linking woody and tree growth forms to elevated LysM-RLK, Malectin-RLK, and several LRR-RLK subclasses. Under phylogenetic correction across all 39 families, however, no family survived joint FDR correction for either the woody/non-woody or the tree-versus-herb contrast (LysM-RLK closest, FDR p = 0.13). LysM-RLK, a pre-specified focal family, remained the strongest and most consistent signal - elevated in woody and tree species under both non-parametric (FDR p = 0.004) and phylogenetic tests, significant when evaluated within the 12 principal receptor families (p = 0.007) and robust to branch-length scaling, taxon subsampling, domestication, and genome size, but not significant under the more conservative joint correction across all 39 annotated families (FDR p = 0.13). Conclusion Across angiosperms, climate and geography are not robust predictors of immune receptor gene content once shared ancestry is taken into account. The more consistent correlate of immune gene number is growth form: woody and tree species tend to carry more LysM-RLK and other cell-surface receptor genes than herbs, a pattern not explained by ambient pathogen exposure. Whether this reflects pathogen immunity or mycorrhizal symbiosis cannot be resolved from aggregate gene counts and is a priority for future work.