Genome-Wide Characterization Highlights Key Roles for Bread Wheat MLO Genes in Powdery Mildew and Abiotic Stresses

Powdery mildew (PM) is one of the most devastating and widespread foliar diseases globally. Despite the critical need for developing a durable PM resistance, the number of cloned genes remains limited, along with a shortage of Mildew Locus O (MLO) resistance-conferring genes in wheat breeding programs. Here, utilizing the latest wheat reference genome data, we comprehensively identified and characterized 47 MLO genes through a genome-wide search approach. These genes are randomly distributed among 21 wheat chromosomes, harbor seven transmembrane domains, and are predicted to be primarily localized in the plasma membrane. Comparative phylogenetic analysis with model plants classified wheat MLOs into four clades (I-IV) harboring 6, 28, 6, and 7 genes, respectively. The phylogenetic grouping was strongly supported by gene structures and motif distribution among members of different clades. Evolution analysis revealed that the MLO gene arsenal expanded through segmental duplications, and purifying selection is potentially conserving their stress-associated functions. In-silico expression analysis highlighted at least 10 genes with overlapping expression patterns among different growth and development stages and under abiotic and biotic stress conditions. The quantitative real-time polymerase chain reaction (qRT-PCR) validated the differential expression patterns of these 10 overlapping genes in PM-resistant and susceptible wheat genotypes after challenging these with a PM pathogen strain at different time intervals. The identified wheat MLO genes, especially the 10 overlapping genes, highlight untapped genetic diversity for engineering a durable and broad-spectrum tolerance/resistance against abiotic and biotic stresses, especially the PM resistance. Collectively, this study provides a compendium of wheat MLO genes, which could be functionally characterized to confirm their roles in PM resistance and further exploited in wheat breeding programs for the development of climate-resilient cultivars for sustainable wheat production.