The effect of constitutive root isoprene emission on root phenotype and physiology under control and salt stress conditions

Abstract

ABSTRACTIsoprene, a volatile hydrocarbon, is typically emitted from the leaves and other aboveground plant organs; isoprene emission from roots is not well studied. Given its well-known function in plant growth and defense aboveground, isoprene may also be involved in shaping root physiology to resist belowground stress. We used isoprene-emitting transgenic lines (IE) and a non-emitting empty vector and/or wild type lines (NE) of Arabidopsis to elucidate the roles of isoprene in root physiology and salt stress resistance. We assessed root phenotype and metabolic changes, hormone biosynthesis and signaling, and stress-responses under normal and saline conditions of IE and NE lines. We also analyzed the root transcriptome in the presence or absence of salt stress. IE lines emitted isoprene from roots, which was associated with higher primary root growth, root biomass, and root/shoot biomass ratio under both control and salt stress conditions. Transcriptome data indicated that isoprene altered the expression of key genes involved in hormone metabolism and plant responses to stress factors. Our findings reveal that root constitutive isoprene emission sustains root growth also under salinity by regulating and/or priming hormone biosynthesis and signaling mechanisms, amino acids biosynthesis, and expression of key genes relevant to salt stress defense.