**1. Introduction**

Climatic conditions are important for the well-functioning of any ecosystem. Altered climatic conditions have direct effects on plant health, productivity, and yield. Earth's climate is changing very rapidly mainly due to human activities, having negative effects on human and the ecosystem (particularly on the agriculture sector) [1]. Altered climatic conditions contribute negatively due to increased levels of greenhouse gases, global warming, higher emission of CO2, deforestation, and excessive use of fossil fuels. Plants are the primary producers and a very important component of the ecosystem. Temperature fluctuations, particularly due to altered climate conditions, may trigger other factors, such as drought, flood, soil erosion, waterlogging, and salinity, which ultimately led to lower crop productivity and yield. As the world population is increasing rapidly, demand for the food is also increasing. We need good quality and quantity of crops to fulfill the feeding requirements of the world population. Natural stress factors (light intensity, temperature, water stress, and nutrient availability) and anthropogenic stress factors (mainly HM pollution, excessive use of herbicides, acid rain, and enhanced UV-B radiations) contribute strongly to deteriorate crop health and productivity. Continuously changing climatic conditions induce higher stress on crops due to irregular patterns of moisture contents, more pest and disease infection, more waterlogging conditions, increased soil erosion, and global warming [2]. Climate change and food shortage are the most challenging factors of this century, which need our serious efforts and attention. It is very important to develop crops that are better able to tolerate abrupt climate changes and associated abiotic stresses to keep a balance between environment and agricultural crop production [3]. Among other techniques, the plant genetic engineering approach could also be used for abiotic stress management in crops. Transgenic plants have better tolerance level to various kinds of abiotic stress. They also have improved fruit quality, shelf life, and plant architecture. Genetic engineering of plants also results in reduced postharvest losses, which improve productivity and yield [4]. Induction of the expression of stress-related TFs (MYC, bzip, DREB1A, DREB1B, DREB1C, CBF1, CBF2), stress-responsive genes, signaling pathway kinases (MAPK, CDPK, S6K, PIP5K) hormonal biosynthesis (ABA, ethylene), antioxidant and ROS scavenging mechanism (APX, GSH, GR, GST, SOD, flavonoids, carotenoids), regulatory proteins (HSPs, LEA, dehydrins, aquaporins, metallothioneins, phytochelatins) osmolytes, and compatible solutes (proline, sorbitol, mannitol, polyamines, amino acids, glycine betaine), transporters (NHX, HKT, HMAs) improve the crop performance under altered environmental conditions. Through genetic engineering and genome editing tools, transgenic plants have developed, which are better able to adapt to climate changes without affecting their productivity and yield. Genotyping, sequencing, transcriptomics, proteomics, metabolomics, and functional genomics can be integrated collectively for the identification of stress-responsive genes/gene products and their expression in targeted plants to develop abiotic stress-tolerant cultivars [3]. Different genome editing tools are being used like CRIPR/Cas9, which is of prime importance due to its rapid and effective outcomes. It is an environment-friendly technique to produce transgenic plants, which are better adapted to stress conditions that emerges due to climate change. The CRISPR system is based on candidate gene knockout/insertion or gene replacement, which results in either loss of function, downregulated, or over-expression of gene for abiotic stress tolerance [5].
