Ethanol induces heat tolerance in plants by stimulating unfolded protein response.

KEY MESSAGE: Ethanol priming induces heat stress tolerance by the stimulation of unfolded protein response. Global warming increases the risk of heat stress-related yield losses in agricultural crops. Chemical priming, using safe agents, that can flexibly activate adaptive regulatory responses to adverse conditions, is a complementary approach to genetic improvement for stress adaptation. In the present study, we demonstrated that pretreatment of Arabidopsis with a low concentration of ethanol enhances heat tolerance without suppressing plant growth. We also demonstrated that ethanol pretreatment improved leaf growth in lettuce (Lactuca sativa L.) plants grown in the field conditions under high temperatures. Transcriptome analysis revealed a set of genes that were up-regulated in ethanol-pretreated plants, relative to water-pretreated controls. Binding Protein 3 (BIP3), an endoplasmic reticulum (ER)-stress marker chaperone gene, was among the identified up-regulated genes. The expression levels of BIP3 were confirmed by RT-qPCR. Root-uptake of ethanol was metabolized to organic acids, nucleic acids, amines and other molecules, followed by an increase in putrescine content, which substantially promoted unfolded protein response (UPR) signaling and high-temperature acclimation. We also showed that inhibition of polyamine production and UPR signaling negated the heat stress tolerance induced by ethanol pretreatment. These findings collectively indicate that ethanol priming activates UPR signaling via putrescine accumulation, leading to enhanced heat stress tolerance. The information gained from this study will be useful for establishing ethanol-mediated chemical priming strategies that can be used to help maintain crop production under heat stress conditions.

The duration of ethanol-induced high-salinity stress tolerance in Arabidopsis thaliana.

High-salinity stress affects plant growth and crop yield, so the development of techniques to enhance plant tolerance to such stress is important. Recently, we revealed that ethanol enhances high-salinity stress tolerance in Arabidopsis thaliana and rice by detoxifying Reactive Oxygen Species (ROS). However, we did not investigate how long salt stress tolerance was maintained following treatment with ethanol. Therefore, we herein analyzed survival rates and expression levels of AtZAT12, which is a transcriptional factor of ROS detoxification enzymes, under different conditions in Arabidopsis. Our results showed that ethanol-mediated high-salinity stress tolerance was lost after a 24 h break in ethanol treatment in ~ 1-week-old plants. Although ethanol enhanced salt stress tolerance, high concentrations of ethanol negatively affected plant growth. Thus, these data support the idea that adjustments of the frequency and amount of ethanol application to plants is useful to enhance salt stress tolerance without growth inhibition in the agricultural field.