Urban Air Pollution and Plant Tolerance: Omics Responses to Ozone, Nitrogen Oxides, and Particulate Matter

Abstract

Urban air pollution is a crucial global challenge, mainly originating from urbanization and industrial activities, which are continuously increasing. Vegetation serves as a natural air filter for air pollution, but adverse effects on plant health, photosynthesis, and metabolism can occur. Recent omics technologies have revolutionized the study of molecular plant responses to air pollution, overcoming previous limitations. This review synthesizes the latest advancements in molecular plant responses to major air pollutants, emphasizing ozone (O₃), nitrogen oxides (NO_X), and particulate matter (PM) research. These pollutants induce stress responses common to other abiotic and biotic stresses, including the activation of reactive oxygen species (ROSs)-scavenging enzymes and hormone signaling pathways. New evidence has shown the central role of antioxidant phenolic compound biosynthesis, via the phenylpropanoid pathway, in air pollution stress responses. Transcription factors like WRKY, AP2/ERF, and MYB, which connect hormone signaling to antioxidant biosynthesis, were also affected. To date, research has predominantly focused on laboratory studies analyzing individual pollutants. This review highlights the need for comprehensive field studies and the identification of molecular tolerance traits, which are crucial for the identification of tolerant plant species, aimed at the development of sustainable nature-based solutions (NBSs) to mitigate urban air pollution.

Keywords: nitrogen dioxide; ozone; particulate matter; phenylpropanoids; photosynthesis; plant species; reactive oxygen species; transcription factors.

Figure 1

Representative image of the main natural and human sources of primary and secondary air pollutants. Arrows in the clouds indicate the photochemically-driven generation of secondary air pollutants from the primary ones. In detail symbols indicate: PM, particulate matter; HMs, heavy metals; VOCs, volatile organic compounds; CO, carbon monoxide; NOx, nitrogen oxides; SOx, sulfur oxides; PAHs, polycyclic aromatic hydrocarbons; O₃, ozone; H₂SO₄, sulfuric acid; HNO₃, nitric acid.

Figure 2

Schematic representation of the pathways affected by O₃ (ozone) in plants. Sharp arrows and blunt arrows indicate induction and repression in pathways, respectively. Red squares enclose genes, while blue squares enclose proteins, affected by O₃.

Figure 3

Schematic representation of the pathways affected by NO₂ (nitrogen dioxide) in plants. Sharp arrows and blunt arrows indicate induction and repression in pathways, respectively. Red squares enclose genes, while blue squares enclose proteins, affected by NO₂. Pathways that are not primarily involved are shaded.

Figure 4

Schematic representation of the pathways affected by PM and PM-containing HMs (particulate matter, heavy metals) in plants. Sharp arrows and blunt arrows indicate induction and repression in pathways, respectively. Red squares enclose genes, while blue squares enclose proteins, affected by PM and HMs.

Figure 5

Schematic diagram of the pathways affected by the most common urban air pollutants in plants. Sharp arrows and blunt arrows indicate induction and repression in pathways, respectively.