REVIEW Plant small RNAs: the essential epigenetic regulators of gene expression for salt-stress responses and tolerance Vinay Kumar 1,2 • Tushar Khare 1 • Varsha Shriram 3 • Shabir H. Wani 4,5 Received: 17 July 2017 / Accepted: 12 September 2017 Ó Springer-Verlag GmbH Germany 2017 Abstract Saline environment cues distort the plant growth, development and crop yield. Epigenetics has emerged as one of the prime themes in plant functional genomics for molecular-stress-physiology research, as copious studies have provided new visions into the epige- netic control of stress adaptations. The epigenetic control is associated with the regulation of the expression of stress- related genes which also comprises many steady alterations inherited in next cellular generation as stress memory. These epigenetic amendments also implicate induction of small RNA (sRNA)-mediated fine-tuning of transcriptional and post-transcriptional regulations of gene expression. These tiny (19–24 nt) RNA species, particularly micro- RNAs (miRNAs) besides endogenous small interfering RNA (siRNA) have emerged as important responsive entities for epigenetic modulation of salt-stress effects on plants. There is a recent upsurge in development of tools and databases useful for prediction, identification and validation of small RNAs (sRNAs) and their target mes- senger RNAs (mRNAs). Therefore, these small but key regulatory molecules have received a wide attention in post-genomic era as potential targets for engineering stress tolerance in major glycophytic crops, though it is yet to be explored optimally. This review aims to provide critical updates on plant sRNAs as key epigenetic regulators of plant salt-stress responses, their target prediction and val- idation, computational tools and databases available for plant small RNAs, besides discussing their roles in salt- stress regulatory networks and adaptive mechanisms in plants, with special emphasis on their exploration for engineering salinity tolerance in plants. Keywords Salinity stress Á Epigenetic regulations Á Non- coding RNAs Á microRNA Á Short interfering RNAs Á Post- transcriptional regulation Á Stress responses Á Genetic engineering Introduction Soil salinization has emerged as a major threat to crop production, causing substantial losses to crop yields besides hampering the quality of produce worldwide (Pathak et al. 2014; Kumar and Khare 2015; Pathak and Wani 2015; Wani and Hossain 2015; Kumar et al. 2017). The severity has worsened in recent times particularly in arid and semi-arid lands where water evapotranspiration Communicated by Tarek Hewezi. For special issue on: ‘‘Epigenetic regulation of plant development and stress responses’’ in Plant Cell Reports. & Vinay Kumar vinaymalik123@gmail.com & Shabir H. Wani shabirhussainwani@gmail.com 1 Department of Biotechnology, Modern College of Arts, Science and Commerce (Savitribai Phule Pune University), Ganeshkhind, Pune 411016, India 2 Department of Environmental Science, Savitribai Phule Pune University, Ganeshkhind, Pune 411007, India 3 Department of Botany, Prof. Ramkrishna More College (Savitribai Phule Pune University), Akurdi, Pune 411044, India 4 Mountain Research Centre for Field Crops, Sher-e-Kashmir University of Agricultural Sciences and Technology of Kashmir, Khudwani, Anantnag, Jammu and Kashmir 192101, India 5 Department of Plant Soil and Microbial Sciences, Michigan State University, East Lansing, MI, USA 123 Plant Cell Rep DOI 10.1007/s00299-017-2210-4