Canalized gene regulatory networks stabilize floral polymorphism and enable modular transgressive expression

Abstract

O_LIFloral polymorphisms frequently persist across heterogeneous environments despite ongoing gene flow, yet the regulatory mechanisms maintaining discrete phenotypes remain unclear. We tested whether alternative flower-colour morphs in Stellera chamaejasme L. are maintained by canalized gene regulatory architectures that stabilize expression around morph-specific optima. C_LIO_LIWe used a pan-transcriptomic and eco-evolutionary framework integrating genome-wide gene expression profiling, co-expression network analysis, functional enrichment, ortholog-based phylogenomics, and variance-based modeling of regulatory canalization and transgressive expression to quantify regulatory variation across morphs. C_LIO_LITranscriptomic variation was structured primarily by morph identity rather than geography, indicating consistent morph-associated regulatory programs. Parental morphs showed reduced within-morph variance in gene co-expression modules, consistent with strong regulatory constraint at the network level. In contrast, a naturally occurring mosaic morph exhibited extensive non-additive and predominantly transgressive expression, with most genes falling outside the parental range. This transgressive signal was modular, with most networks remaining stable while a subset showed elevated variance and disrupted inheritance. Functional analyses further reveal that floral pigmentation is embedded within broader metabolic and stress-response pathways, linking color polymorphism to coordinated physiological states and ecological differentiation. C_LI