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In recent years, anthropogenic activities and climate change have significantly increased exposure of plants to environmental stresses (single or multiple) and pollutants, with negative consequences for the survival and productivity of vegetation. Plants may activate an armament of defenses against stresses. Isoprene, the most abundant biogenic volatile organic compound (BVOC) emitted by plants, is supposed to have a direct or indirect antioxidant role by quenching reactive oxygen species (ROS) or by reprogramming gene expression for antioxidant activation. On the other hand, isoprene is involved in the chemistry of troposphere, further contributing to a build up of pollutants when mixing with anthropogenic gases. In this review, we summarize present knowledge on the impact of air and soil pollutants on isoprene emission by plants, indicating possible feedback and feedforward mechanisms that may affect whole ecosystem functioning and evolution of plant species. 

Abstract Isoprene, a volatile hydrocarbon, is typically emitted from the leaves of many plant species. Given its well‐known function in plant growth and defense aboveground, we examined its effects on root physiology. We used isoprene‐emitting (IE) lines and a non‐emitting (NE) line of Arabidopsis and investigated their performance by analyzing root phenotype, hormone levels, transcriptome, and metabolite profiles under both normal and salt stress conditions. We show that IE lines emitted tiny amounts of isoprene from roots and showed an increased root/shoot ratio compared with NE line. Isoprene emission exerted a noteworthy influence on hormone profiles related to plant growth and stress response, promoting root development and salt‐stress resistance. Methyl erythritol 4‐phosphate pathway metabolites, precursors of isoprene and hormones, were higher in the roots of IE lines than in the NE line. Transcriptome data indicated that the presence of isoprene increased the expression of key genes involved in hormone metabolism/signaling. Our findings reveal that constitutive root isoprene emission sustains root growth under saline conditions by regulating and/or priming hormone biosynthesis and signaling mechanisms and expression of key genes relevant to salt stress defense.