Molecular dissection of the role of Aucsia-1 and Aucsia-2 in tomato root development

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 Aucsia-1 and Aucsia-2 in the tomato cultivar MicroTom using the CRISPR-Cas9 tool. The aim of this study is to dissect the role of the two genes in root development, with the future perspective of designing 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 homozygous aucsia-1 and homozygous aucsia-2 mutants that appeared indistinguishable from WT plants in terms of shoot architecture and leaf morphology. The knock-out mutation of the Aucsia-1 and Aucsia-2 genes caused different alterations in root development. The aucsia-1 mutants displayed an increased lateral root length, while the Aucsia-2 mutation caused a reduction in lateral root density. Using in vitro tests and a hydroponic system, we evaluated whether the parsimonious root phenotype of aucsia-2 mutants could confer an increased capacity to cope with salinity stress, and whether the changes in lateral root growth in the aucsia-1 mutants can be advantageous under osmotic stress.