Crops exposed to extreme conditions: perspectives of gene editing to improve stress tolerance

Extreme environmental conditions, such as drought, soil salinity, and extreme temperatures, seriously limit agricultural production. Traditional breeding can produce more tolerant cultivars, but has limitations due to the multigene-encoded traits and long time needed to generate improved varieties. Gene editing can introduce single or multiple point mutations, generate microinsertion/deletions (InDel), modify selected bases or DNA fragments, and modulate gene expression, producing novel alleles resembling natural variability. In this review, we cover the strategies and perspectives for editing nuclear or organelle-encoded genes to enhance tolerance to extreme environmental conditions, such as drought, salinity, cold, and heavy metals. A list of 73 arabidopsis genes is assembled, whose function in abiotic stress responses has been demonstrated with insertion or gene-edited mutants. A collection of 97 gene-edited mutants in crops with tolerance to one or more abiotic stresses was compiled. The power of multiplex editing is demonstrated to target multigene-encoded traits related to stress tolerance. Special attention is paid to encouraging results of 20 gene editing programs in various crops, which confirmed improved tolerance in field conditions, demonstrating the feasibility to incorporate this powerful technology into plant breeding. As gene editing generates molecular changes similar to natural polymorphism, legal conditions adopting NGT-friendly frameworks are expected to facilitate commercialization of such engineered varieties in most countries.