Evolutionary constraints and regulatory plasticity shape host specialization in the Magnaporthe oryzae species complex.

Rice blast caused by Magnaporthe oryzae threatens global rice production, and wheat blast emergence highlights the pathogen's capacity for host shifts. Although numerous studies have described M. oryzae genome organization and infection mechanisms, critical questions remain regarding the evolutionary drivers of stable host specialization. Importantly, the blast pathogen comprises a species complex of genetically differentiated, host-adapted lineages rather than single homogeneous species. To address this knowledge gap, we integrate evidence from evolutionary genomics, transcriptomics, and metabolomics to develop the "Constrained Plasticity" framework. We argue that host adaptation arises from three interacting layers: genomic scaffolding (including epigenetic and noncoding RNA regulation), regulatory networks (enabling transcriptional plasticity), and metabolic compatibility (determining physiological success). This systems-level perspective explains the long-term stability of host-adapted lineages and the rare breakdowns resulting in host shifts, such as wheat blast. This framework generates testable predictions for pathogen emergence and provides a roadmap for developing lineage-aware resistance strategies.