GENETIC AND MOLECULAR MECHANISMS OF ABIOTIC STRESS TOLERANCE IN HORTICULTURAL CROPS: ADVANCES IN GENOMICS AND GENOME EDITING- A REVIEW

Abstract

Abiotic stresses such as drought, salinity, heat, chilling, freezing, flooding, nutrient deficiency, heavy-metal toxicity and excessive radiation have a great impact on the yield and quality of horticulture crops. These products are especially susceptible as commercial success relies on yield, visual appearance, flavour, texture, nutritional makeup and postharvest behaviour. Stress tolerance is established through integrated processes, including environmental sensing, calcium and reactive oxygen species signaling, hormonal interplay, transcriptional control, ion homeostasis, osmotic adjustment, antioxidant defense, proteome protection, metabolic reprogramming and developmental pliancy. These phenotypic responses are governed by complex genetic bases, characterized by QTL, structural variations, regulatory polymorphisms, gene-family expansion, epistasis and genotype-by-environment interactions. Developments in long read sequencing including haplotype-resolved assemblies, pangenomics, genome-wide association studies, transcriptomics, epigenomics, proteomics, metabolomics, phenomics and envirotyping are allowing access to adaptive genes and alleles not available previously. CRISPR-Cas systems also allow their specific validation and modification, while base editing, prime editing, multiplex editing, CRISPR-mediated gene regulation provide superior precision to conventional methods of gene disruption. Nevertheless, transformation recalcitrance, polyploidy, heterozygosity, long juvenile periods, pleiotropic growth penalties and lack of sufficient field validation are still substantial obstacles in this regard. In this review, the genetic and molecular bases of abiotic-stress tolerance are discussed and how genomics and genome editing technologies can contribute to the development of robust, high yielding and high-quality horticultural cultivars.