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

ABSTRACT 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.