Overexpression of Isoprene Synthase Affects ABA- and Drought-Related Gene Expression and Enhances Tolerance to Abiotic Stress

Abstract

Isoprene is the most abundant single biogenic volatile compound emitted by plants. Despite the relevance of this molecule to plant abiotic resistance and its impact on global atmospheric chemistry, little is known about the details of its mechanism of action. Here, we characterized through both physiological and molecular methods the mechanisms of action of isoprene using model transgenic arabidopsis lines overexpressing a monocot isoprene synthase gene. Our results demonstrated the effect that isoprene had on ABA signaling at different tissue-specific, spatial, and temporal scales. In particular, we found that isoprene enhanced stomatal sensitivity to ABA through upregulation of RD29B signaling gene. By contrast, isoprene decreased sensitivity to ABA in germinating seeds and roots, suggesting tissue-specific mechanisms of action. In leaves, isoprene caused the downregulation of COR15A and P5CS genes, suggesting that the enhanced tolerance to water-deprivation stress observed in isoprene-emitting plants may be mediated chiefly by an enhanced membrane integrity and tolerance to osmotic stress.

Isoprene: An Antioxidant Itself or a Molecule with Multiple Regulatory Functions in Plants?

“…Early unpublished experiments suggested a priming effect of isoprene, as isoprene-emitting plants showed higher activities of enzymatic antioxidants and higher levels of heat shock factors and proteins ahead of a heat stress from which they were then more protected than non-emitters (Loreto et al personal communication). A very recent report seems to confirm a sort of priming effect for isoprene in transgenic Arabidopsis lines overexpressing an isoprene synthase gene [ 53 ]. In particular, these transgenic, isoprene-emitting lines were found to reduce water loss, enhance ABA-induced stomatal closure, and enhance the expression of the ABA-responsive gene RD29B after ABA treatment [ 53 ].…”

“…A very recent report seems to confirm a sort of priming effect for isoprene in transgenic Arabidopsis lines overexpressing an isoprene synthase gene [ 53 ]. In particular, these transgenic, isoprene-emitting lines were found to reduce water loss, enhance ABA-induced stomatal closure, and enhance the expression of the ABA-responsive gene RD29B after ABA treatment [ 53 ]. In summary, isoprene-emitting lines were more tolerant to dehydration and heat stress by acquiring an enhanced responsiveness to ABA [ 53 ].…”

“…This study revealed an induction of chloroplast, phenylpropanoid biosynthetic and translation machinery genes, as well as of transcription factor-enriched gene networks. Another study showed that Arabidopsis plants that can emit isoprene because of IspS insertion were more sensitive to exogenous ABA supplement, which leads to an upregulation of RD29B, a gene involved in abscisic acid-activated signaling pathway [ 53 ]. In contrast, under water-stress, the genes COR15A, whose role is to protect stromal proteins, and P5CS, involved in protection from reactive oxidative species, were both downregulated in isoprene-emitting compared to non-emitting Arabidopsis [ 53 ].…”

“…Another study showed that Arabidopsis plants that can emit isoprene because of IspS insertion were more sensitive to exogenous ABA supplement, which leads to an upregulation of RD29B, a gene involved in abscisic acid-activated signaling pathway [ 53 ]. In contrast, under water-stress, the genes COR15A, whose role is to protect stromal proteins, and P5CS, involved in protection from reactive oxidative species, were both downregulated in isoprene-emitting compared to non-emitting Arabidopsis [ 53 ]. Isoprene-induced modulations of gene expression and pathway interactions were reviewed in detail by Monson et al [ 54 ], and interpreted by the authors as an indication of isoprene potential role in mediating growth-defense tradeoff (see below).…”

“…Isoprene-emitting Arabidopsis plants transformed with the IspS gene from Eucalyptus globulus showed increased hypocotyl, cotyledon, leaf and inflorescence growth, suggesting that isoprene may exert its effects on growth through direct regulation of gene expression [ 51 ]. In a different study, isoprene-emitting Arabidopsis plants transformed with the IspS gene from Arundo donax showed reduced growth inhibition after exogenous ABA treatment [ 53 ]. On the other hand, negative effects of isoprene on leaf and stem growth were observed in isoprene-emitting tobacco lines.…”