8. Future and perspectives
Understanding how plants adapt their root system under changing environmental conditions to ensure the continued uptake of water and nutrients is essential for future breeding programs. Due to the increased occurrence of weather extremes, crops will need to be adapted more quickly in the future. Previous classical methods, such as cross-breeding and selection, are not sufficient for this purpose. CRISPR/Cas technology has proven to be a tool that allows precisely targeted modification of the target sequence. By refining the methods (base editing, prime editing) or tissue-specific expression of the double-strand break-inducing agents, the often pleiotropic effect of different mutations can be circumvented. The examples shown in the table can also be applied to other crops. For instance, it would be interesting to see if the DRO1 gene studied in rice plays a role in other cereals’ salt and drought stress tolerance. Since knockout of the CKX genes in barley did not lead to the results obtained in maize, tissue-specific expression of the molecular scissors could be used as an alternative to circumvent adverse pleiotropic effects. Furthermore, Cas fusion proteins show real potential for activating or repressing the mentioned genes.
Molecular mechanisms of hormonal influence on root growth have relevance for the plant’s abiotic and biotic interaction. This requires knowledge of the metabolism and signalling pathways involved. Also, specificity of molecular regulation exists among cereals, depending on their growth habitat. Although some futures have been conserved during evolution, there are variations between the dicot model plants to cereals. Therefore, interest should also be given to more minor or non-cereal plants.
Because targeting the hormone metabolism and signalling pathway has very often adverse pleiotropic effects, one should consider focusing on the downstream events specific to RSA regulation. For example, targeting the root angle would have extreme advantages for the plant in periods of temporary drought. At the same time, mechanical anchoring of the plant would be improved, which could be advantageous during strong winds or thunderstorms. It is also interesting to improve the nutrient uptake of the root by soil microbes. By targeting secreted signals, the microbial community surrounding the root can be influenced.
In summary, CRISPR/Cas technology with its multiple variants and fusion possibilities allow for an incredible variety of modifications. In the future, this will enable a more targeted and rapid transfer of primary research results into current breeding programs.