Genome editing of Aucsia-2 in MicroTom as a proof-of-concept to obtain a tomato ideotype for cultivation under adverse environmental conditions

Genome editing is an approach to accelerate breeding for crop improvement, particularly for plant species with well-characterized genetic and genomic resources, such as tomato. Genome editing allows customized modifications of target genes to achieve desired agronomic traits in a fairly predictable manner. Starting from a genetic resource identified in our laboratory, the Aucsia genes implicated in auxin-related fruit set and root development, we generated stable mutants of Aucsia2 in the tomato cultivar MicroTom using the CRISPR-Cas9 tool. The aim of this study is to obtain a tomato ideotype that combines the maintenance of high fruit set capacity with positive effects in root development, permitting adaptation to a changing environment. We obtained three T2 homozygous aucsia-2 mutants that were indistinguishable from WT plants in terms of shoot architecture and leaf and fruit morphology. Under conditions hindering pollination, the aucsia2 mutants showed a lower proportion of aborted ovaries than WT plants. The Aucsia-2 mutation affected root architecture, causing a reduction in the number and density of lateral roots. This root modification confers an advantage under salt stress, as the aucsia-2 mutants accumulated less Na in the shoots and displayed a less pronounced halotropic response than WT plants, a behavior that may be explained by the higher concentration of trehalose in aucsia-2 shoots compared to WT.