Identification and Expression Analysis of <i>MLO</i> Genes in <i>Poa pratensis</i> L. in Response to Powdery Mildew caused by <i>Blumeria graminis</i> f. sp. <i>poae</i>

Poa pratensis L. is an important perennial grass that is widely used in seed and sod production for turfgrass establishment. However, its health and aesthetic value are frequently threatened by powdery mildew infection. In this study, the MLO genes of P. pratensis were identified through transcriptome analysis of Kentucky bluegrass in response to Blumeria graminis f. sp. poae. A comprehensive bioinformatics analysis, including physicochemical characterization, protein interaction prediction, EggNOG annotation, domain identification, and phylogenetic reconstruction, was conducted. Expression profiling revealed distinct patterns of PpMLO gene expression among varieties with different resistance levels. In this study, 33 PpMLO genes were identified from transcriptome data of under powdery mildew stress. Transmembrane domain analysis revealed that seven PpMLO proteins contain seven transmembrane domains, with leucine being the most abundant amino acid. The protein interaction network suggested a coordinated signaling system involving seven PpMLO proteins and functional proteins from Oryza sativa L. GO analysis revealed that the core members of the PpMLO gene family regulate immune and stress response biological processes by targeting the membrane and endomembrane systems and through molecular functions such as enzyme activities and ubiquitination. Phylogenetic analysis revealed that the PpMLO gene family members of P. pratensis clustered in the same group as the homologous MLO genes of Arabidopsis thaliana and O. sativa, suggesting that they may have conserved biological functions in the response to powdery mildew stress. Expression profiling revealed three key candidate genes, PpMLO2, PpMLO13, and PpMLO14, exhibited distinct expression patterns across cultivars with varying resistance levels. In the moderately resistant cultivar 'Taihang', PpMLO2 and PpMLO13 were significantly upregulated (Log2 fold change = 6.31 and 6.21, respectively). In the highly susceptible cultivar 'Explorer', PpMLO13 was moderately upregulated (Log2 fold change = 3.85). In contrast, PpMLO14 was strongly downregulated in the susceptible cultivar 'Black Jack' (Log2 fold change = -6.82). These differential expression patterns indicate that the MLO signaling pathway may adopt distinct regulatory strategies depending on the genetic background of the host. The identification of PpMLO2, PpMLO13, and PpMLO14 as key susceptibility candidates provides clear targets for precision molecular breeding. Targeting these genes through gene silencing or genome editing represents a promising strategy for reducing reliance on chemical fungicides and promoting sustainable green management of powdery mildew in P. pratensis.