Ethanol (C2H5OH) involvement in plant abiotic stress response

In view of climate change-exacerbated abiotic stresses, innovative solutions that complement genetic approaches have become increasingly necessary to help crops adapt to the harsh environments. Ethanol (C2H5OH, or simply EtOH), a short-chain small volatile molecule and ubiquitous in nature, has been recently shown to alleviate abiotic stress-induced damages in plants, revealing a novel potent strategy for enhancing plant abiotic stress tolerance. Whereas higher doses (> 300 mM) are usually injurious to plants, several studies have shown that low concentrations of EtOH (μM to mM range) mediate plant stress responses and adaptation. Both stress-induced elevated endogenous biosynthesis and exogenous application of EtOH have been shown to play a role in this regard. Numerous studies using different species have shown that EtOH modulates several physiological and molecular processes underpinning plant stress tolerance, including regulation of stomatal closure, leaf transpiration rate, leaf water content, antioxidant capacity, biosynthesis of sugars, and activation of stress-responsive genes and unfolded protein response. However, a survey of the literature shows that the role of EtOH in plant abiotic stress response is just beginning to be elucidated. Here, therefore, the recent insights on EtOH-mediated abiotic stress tolerance mechanisms are parsed together, revealing a potential area for abiotic stress tolerance improvement in crops. A brief overview of endogenous plant EtOH biosynthesis is first provided. Then, the endogenous EtOH concentrations that have been observed in various plant species under different stress conditions are highlighted. The effects of exogenously applied EtOH on growth and physiology in different plant species are also examined. Further, the possible EtOH sensing and signaling mechanisms in plants are discussed, before the role of EtOH in plant abiotic stress tolerance is synthesized. The paper concludes by proffering some perspectives, pointing out some open questions to inspire future research on EtOH-mediated abiotic stress tolerance improvement in crops.