The improved auxin signalling via entire mutation enhances aluminium tolerance in tomato

Acidic soils limit food production in many developing countries by promoting the solubilization of aluminium (Al) cations. Consequently, roots absorb this metal from soil solution, arresting their growth while reducing water and nutrient uptake. To mitigate the impacts of Al, plants rewire their metabolism and growth, with diverse mechanisms in this process shaped by changes in auxin signalling. Here, we present a comprehensive study on the significance of auxin signalling for Al tolerance. We used tomato mutants with reduced (diageotropica, dgt) and increased (entire) auxin sensitivity to assess the regulation of growth and metabolism in plants coping with Al toxicity. Our results indicated a reduced Al tolerance in the dgt mutant, whereas entire was able to tolerate toxic levels of Al. This contrast can be explained by a differential accumulation of reactive oxygen species (ROS) in the root transition zone, where dgt exhibited more differentiated cells, making the pericycle evident. In contrast, entire showed only slight alterations in the transition zone, with root meristematic cells maintaining a reduced level of cell differentiation, which can be associated with sustained growth under toxic Al levels. These differences were followed by alterations in metabolites related to Al sensitivity in the roots of dgt plants, whereas the entire mutant exhibited only slight metabolic changes. Collectively, our results suggest that genetic modifications to regulate auxin perception have the potential to increase Al tolerance in crops.