Uncovering alternative physiological and molecular strategies to cope with water stress in olive tree

In recent years, the ongoing climate changes have made it crucial to rethink agriculture in a more sustainable way. This includes reducing and optimizing the use of resources, including water, through the identification and selection of genotypes more tolerant to abiotic stresses. Although considered a xerophytic species, the olive tree requires an adequate water supply to ensure both quantity and quality production. Drought-tolerant olive cultivars have been identified through breeding programs; however, the key molecular mechanisms involved in this tolerance remain largely unknown. To investigate in depth the plant responses to drought, six cultivars of different genetic backgrounds were grown in controlled conditions and exposed to water stress as well as inoculated with arbuscular mycorrhizal fungi (AMF). The physiological responses to drought stress varied among cultivars, as expected, showing complementary and/or alternative strategies, even according to AMF inoculation. This approach allowed us to identify two contrasting olive tree cultivars in response to drought stress ("Frantoio" and "Arbequina" as susceptible and tolerant, respectively). Transcriptomic profiles comparison of these cultivars enabled us to identify differentially expressed genes (DEG) with key roles in the regulation of metabolic pathways involved in drought tolerance, useful to support future olive tree breeding programs. Interestingly, the AMF inoculum was able to alleviate water stress damages mainly in the susceptible cultivar; this effect involved the more important plant physiological responses.