Comparative Transcriptomics Reveals Constitutive Immunity and Divergent Defence Strategies in Wheat against Leaf Rust.

Wheat leaf rust, caused by Puccinia triticina, poses a continuous threat to global food security. To dissect durable resistance mechanisms, we compared early infection responses between the near-immune cultivar 'Yunmai 34' (YM) and the susceptible 'Chinese Spring' (CS). While CS exhibited massive transcriptional reprogramming upon infection, YM displayed a relatively narrow scale-changes yet could arrested the pathogen prior to haustorium formation. This resistance might be associated with a constitutive immune state, evidenced by elevated basal expression of pathogenesis-related (PR) genes and defence regulators in the absence of pathogen challenge. Comparatively, CS mobilised a massive differentially expressed genes including those involved in hormone pathways and immune receptors yet insufficient to suppress the pathogen infection. Integrated analysis of differential expression and co-expression networks identified two defence-associated genes encoding an LRR-domain-containing protein (TaLRRop) and an aspartyl-tRNA synthetase (TaAspRS). Functional validation confirmed both as positive regulators contributing to PR- and ROS-associated basal defence. Collectively, these findings demonstrate that a constitutive immune state at the transcriptional level, rather than the overall magnitude of induced responses, underlies effective early resistance to leaf rust, offering valuable target candidates for resistance breeding.