challenges associated with a changing climate. This special issue focuses on plant genetic improvement, especially on the tolerance of plants to stress.Three review papers are included in this special issue. Gerszberg and Hnatuszko-Konka (2017) present an excellent review of the genetic engineering of abiotic stress in tomato. Being adversely affected by various abiotic stresses, tomato provides an excellent research model for the study of these stress tolerance in fleshy fruits. Much effort has been made using genetic engineering to understand stress-related gene expression in tomato, and as such, deserves a comprehensive review. Unlike other reviews that divide this topic into different types of stress, this review focuses on the molecular players involved in stress responses. The review briefly introduces the physiological basis of abiotic stress tolerance in plants then details the approaches to genetic engineering and the achievements in understanding and improving stress tolerance. The review includes: (1) the genetic regulation of various metabolites, including mannitol, glycine betaine, glutathione, unsaturated fatty acids, osmotine, polyamines, and trehalose; (2) the regulation of genes associated with hormone pathways (e.g. ethylene), water channels (e.g. aquaporin) and ion transport; (3) the manipulation of heat shock proteins; (4) the regulation of enzymes in antioxidant systems, such as oxidoreductase, catalase, ascorbate peroxidase, and superoxide dismutase; and (5) the genetic transformation of regulatory genes (e.g. transcription factors and kinases) and other components of signaling systems (e.g. systemin, expansin, and late embryogenesis abundant protein).This review is likely to serve as an informative reference for abiotic stress research in tomato. Singh et al. (2016) present a short review of the roles of cross-talk between microRNA and nitric oxide (NO) in signaling associated with stress responses. MicroRNAs are Genetic engineering and biotechnology are becoming widely used in crop improvement and have provided a means by which increased yields of food and fiber can be produced in an environmentally sustainable manner. In addition, these techniques have allowed us to gain great insights into the networks of genes that result in the production of various bioproducts that can be beneficial for human health and environment. The past 5 years have witnessed substantial breakthroughs in plant genetic engineering and biotechnology. In addition to the manipulation of protein coding genes, microRNAs have proved to be promising targets in crop improvement, and the clustered regularly interspaced short palindromic repeat (CRISPR)-associated endonuclease 9 (CRISPR/Cas9) system has emerged like a radiant sunrise, and has greatly facilitated the targeted modification of specific traits. Reverse breeding technologies are also providing a means of accelerating breeding, allowing new cultivars to be produced to combat the