A comparative analysis of physiological, biochemical, and molecular responses to elevated ozone identifies specific mechanisms of Kentucky bluegrass resistant cultivar

Rapid urbanization and industrialization increase the near-surface concentration of ozone (O3), leading to oxidative damage in plants like turfgrass. However, most studies on turfgrass responses to O3 focus on physiology, rarely exploring molecular mechanisms. Therefore, phenotype, physiological, transcriptomics, and metabolomics were analyzed to investigate the differences in molecular mechanisms between different cultivars in response to O3 stress. In this study, we treated two Kentucky bluegrass (Poa pratensis L.) cultivars (Arcadia and Action) under elevated O3 (EO3, non-filtered ambient air mixed with 80 nmol mol-1 O3) with comparison to non-filtered ambient air (NF). After 9 d of fumigation, the sensitive cultivar Action showed stronger ozone-related responses than the resistant cultivar Arcadia, including leaf visible injury, decrease of chlorophyll content and net photosynthetic rate, and increase of H2O2 and MDA content. Based on observation of epidermal cell structure, Action showed higher stomatal density than Arcadia, potentially resulting in higher O3 influx. Transcriptome analysis indicated that the unique differentially expressed genes (DEGs) of the Arcadia under EO3 vs NF were mainly enriched in photosynthesis, biosynthesis of secondary metabolites, and alpha-linolenic acid metabolism, etc. While the DEGs of the Action were mainly enriched in plant-pathogen interaction, biosynthesis of secondary metabolites, and MAPK signaling pathway. Metabolomic analysis showed that the Arcadia had higher flavonoid content under O3 stress than the Action. Among them, the hormone (JA) and MAPK signaling pathways may play distinct roles in the responses of resistant and sensitive cultivars to O3 stress, respectively. Secondly, the higher flavonoid content in the Arcadia can maintain redox homeostasis, which may contribute to its better performance under O3 stress. These findings offer significant insights into the differential molecular mechanisms underlying the responses of Kentucky bluegrass cultivars to O3 stress, laying the foundation for breeding ozone-resistant cultivar.