Mildew resistance locus O (MLO)-edited petunia shows reduced seed germination, seed set, seed vigor, and growth

In this study, we evaluated the impact of editing the powdery mildew-susceptible gene MLO1 in Petunia hybrida cv. ‘Mirage Rose’ using CRISPR/Cas9. We evaluated plant growth, seed physiology, pollen viability and germination, and gibberellin (GA)-associated gene expression. The mlo1 mutants exhibited delayed seed germination, reduced plant growth, delayed flowering, and lower seed set and weight compared to wild type (WT). While pollen viability and germination were not significantly affected in the mlo1-14 mutant, both were notably reduced in the mlo1-25 mutant. Expression analysis revealed significantly higher levels of GA biosynthesis and receptor genes in the mutants, suggesting alterations in the GA signaling pathways. Application of exogenous GA₃ effectively mitigated growth inhibition in the mutants, aligning their growth parameters with those of WT. Our findings underscore the complex role of MLO1 in regulating plant growth and development, likely through modulation of the GA signaling pathways. This study highlights the trade-offs associated with MLO1 editing for powdery mildew resistance, including impacts on plant growth and reproductive success, and demonstrates the potential of GA₃ application in counteracting these effects. Collectively, this study suggests that the growth penalty and impaired seed physiology caused by the mlo1 mutation must be considered when attempting to edit MLO1 for powdery mildew toleration in ornamental plants, as these drawbacks can severely impact the plants’ utility in the floricultural industry.