Recent trends and advances of RNA interference (RNAi) to improve agricultural crops and enhance their resilience to biotic and abiotic stresses

Over the last two decades, significant advances have been made using genetic engineering technology to modify genes from various exotic origins and introduce them into plants to induce favorable traits. RNA interference (RNAi) was discovered earlier as a natural process for controlling the expression of genes across all higher species. It aims to enhance precision and accuracy in pest/pathogen resistance, quality improvement, and manipulating the architecture of plants. However, it existed as a widely used technique recently. RNAi technologies could well be used to down-regulate any genes' expression without disrupting the expression of other genes. The use of RNA interference to silence genes in various organisms has become the preferred method for studying gene functions. The establishment of new approaches and applications for enhancing desirable characters is essential in crops by gene suppression and the refinement of knowledge of endogenous RNAi mechanisms in plants. RNAi technology in recent years has become an important and choicest method for controlling insects, pests, pathogens, and abiotic stresses like drought, salinity, and temperature. Although there are certain drawbacks in efficiency of this technology such as gene candidate selection, stability of trigger molecule, choice of target species and crops. Nevertheless, from past decade several target genes has been identified in numerous crops for their improvement towards biotic and abiotic stresses. The current review is aimed to emphasize the research done on crops under biotic and abiotic stress using RNAi technology. The review also highlights the gene regulatory pathways/gene silencing, RNA interference, RNAi knockdown, RNAi induced biotic and abiotic resistance and advancements in the understanding of RNAi technology and the functionality of various components of the RNAi machinery in crops for their improvement.

Raising Climate-Resilient Crops: Journey From the Conventional Breeding to New Breeding Approaches

Background

In order to meet the demands of the ever-increasing human population, it has become necessary to raise climate-resilient crops. Plant breeding, which involves crossing and selecting superior gene pools, has contributed tremendously towards achieving this goal during the past few decades. The relatively newer methods of crop improvement based on genetic engineering are relatively simple, and targets can be achieved in an expeditious manner. More recently emerged genome editing technique using CRISPR has raised strong hopes among plant scientists for precise integration of valuable traits and removal of undesirable ones.

Conclusion

Genome editing using Site-Specific Nucleases (SSNs) is a good alternative to the plant breeding and genetic engineering approaches as it can modify the genomes specifically and precisely at the target site in the host genome. Another added advantage of the genome editing approach is the simpler biosafety regulations that have been adopted by many countries for commercialization of the products thus generated. This review provides a critical assessment of the available methods for improving the stress tolerance in crop plants. Special emphasis has been given on genome editing approach in light of the diversity of tools, which are being discovered on an everyday basis and the practical applications of the same. This information will serve as a beginner's guide to initiate the crop improvement programs as well as giving technical insight to the expert to plan the research strategically to tackle even multigenic traits in crop plants.

Gene regulation at transcriptional and post-transcriptional levels to combat salt stress in plants

Soil salinity is a major challenge that will be faced more and more by human population in the near future. Higher salt concentrations in the soil limit the growth and production of crops, which poses serious threats to global food production. Various plant breeding approaches have been followed in the past which are reported to reduce the effect of salt stress by inducing the level of protective metabolites like osmolytes and antioxidants. Conventional breeding approaches are time-consuming and not cost-effective. In recent times, genetic engineering has been largely followed to confer salt tolerance through introgressions of single transgenes or stacking multiple transgenes. However, most of such works are limited only at the laboratory level and field trials are still awaited to prove the long-term efficacy of such transgenics. In this review, we attempt to present a broad overview of the current strategies undertaken to develop halophytic and salt-tolerant crops. The salt-induced damages in the plants are highlighted, followed by representing the novel traits, associated with salt stress, which can be used for engineering salt tolerance in glycophytic crops. Additionally, the role of transcriptional and epigenetic regulation in plants for amelioration of salt-induced damages has been reviewed. The role of post-transcriptional mechanisms such as microRNA regulation, genome editing and alternative splicing, during salt stress, and their implications in the development of salt-tolerant crops are also discussed. Finally, we present a short overview about the role of ion transporters and rhizobacteria in the engineering of salt tolerance in crop species.

Non-Coding RNAs in Response to Drought Stress

Drought stress causes changes in the morphological, physiological, biochemical and molecular characteristics of plants. The response to drought in different plants may vary from avoidance, tolerance and escape to recovery from stress. This response is genetically programmed and regulated in a very complex yet synchronized manner. The crucial genetic regulations mediated by non-coding RNAs (ncRNAs) have emerged as game-changers in modulating the plant responses to drought and other abiotic stresses. The ncRNAs interact with their targets to form potentially subtle regulatory networks that control multiple genes to determine the overall response of plants. Many long and small drought-responsive ncRNAs have been identified and characterized in different plant varieties. The miRNA-based research is better documented, while lncRNA and transposon-derived RNAs are relatively new, and their cellular role is beginning to be understood. In this review, we have compiled the information on the categorization of non-coding RNAs based on their biogenesis and function. We also discuss the available literature on the role of long and small non-coding RNAs in mitigating drought stress in plants.