Drought and salinity, which share a component of osmo-stress, impact significantly plant development and productivity, thus causing serious agricultural yield losses. The molecular mechanisms underlying the response of plants to severe osmo-stress have been studied extensively and, often, are associated to a drastic yield penalty. The current trend in improving crop resistance to osmo-stress is focused on understanding how plants adapt their growth under prolonged and progressive osmo-stress conditions, with the final aim to identify regulatory and structural gene network associated to restoration of a new cellular homeostasis and, ultimately, to resumption of plant growth under limiting environmental conditions. After 25 years of studies on plant’s response to osmo-stress, we reported here our experimental evidences supporting the notion that glycophyte plants, such as potato, when acclimated gradually to osmo-stress, activate regulatory gene networks distinct from those induced upon acute stress. Potato cells gradually acclimated to PEG-induced osmo-stress sustain an active growth, due to a set of metabolic changes, including high proline content, de novo protein synthesis, changes in membrane lipid composition and ethylene accumulation, not induced in cells exposed abruptly to the same stress conditions (Leone et al., 1994, Plant Physiol. 106: 703-712); Leone et al., Plant, Cell and Environ., 1996.19: 1103-1109; Scaramagli et al., 2000, Plant Physiol. Biochem. 38, 345- 351). Extensive remodelling of gene expression depends strictly on duration and intensity of osmo- stress (Ambrosone et al., 2011, Acta Physiol. Plant. 33, 1157-1171; Ambrosone et al., 2017, Gene 15; 597:30-39). Overall, adaptation requires a major effort in terms of transcriptional regulation and distinct transcription factors promote the differential response to short- or long-term stress. Interestingly, modulation of ethylene signalling network appear to be a distinctive trait of gradual adaptation to osmo-stress. Gene expression patterns and functional analyses for adaptive mechanisms were confirmed in planta (Ambrosone et al, 2011; Ambrosone et al., 2017; Ambrosone, Batelli et al., 2015; Plant Physiol. 168:292-306) and may be part of an environmentally-driven epigenetic program, which is under investigation.
