• AMF
• antioxidant capacity
• biostimulant
• Funneliformis mosseae
• gene regulation
• Lactuca sativa L. cv Salinas
• leaf gas exchanges
• mineral nutrition
• nutraceuticals
• RNA-Seq

Lettuce (Lactuca sativa L.) is an annual autogamous diploid plant belonging to Asteraceae and amongst the top ten most profitable crop worldwide due to its nutritional value. Increased cultivation of lettuce has led to major problematics, especially in fertilizer abuse both in soil and extra soil system, which damages the ecosystem and has an increasing cost for the farmers.
Arbuscular mycorrhizal fungi (AMF) are important beneficial microorganisms establishing mutualistic associations with most food crops and are important sustainable tools for nutrient uptake in many plants. In this context, AMF could help reduce the impact of fertilizers, improving plant nutrition, particularly phosphate (P) acquisition, and contributing to growing healthier plants for human consumption.
The first target of my PhD thesis was to evaluate the effect of AM fungus (AMF) Funneliformis mosseae in lettuce plants (Lactuca sativa L. var Salinas) cultivated in soilless culture in greenhouse and growth chamber with low concentrations of phosphorus. Different doses of P concentrations were tested to determinate the best practice: using the lowest possible quantity of P and at the same time avoiding the yield loss of lettuce. Some important bioactive compounds such as leaf content of chlorophylls, carotenoids and phenols were higher in mycorrhizal lettuce plants compared with non-mycorrhizal plants.
The antioxidant capacity in AMF plants showed higher values compared with control plants grown at optimal P nutrition level. Moreover, leaf gas exchanges were higher in inoculated plants than in non-inoculated ones. Nitrogen, phosphorus, and magnesium leaf content was significantly higher in mycorrhizal plants compared with non-mycorrhizal plants grown with the same P level.
These findings suggest that the biostimulant potential of F. mosseae can increase plants’ growth improving the nutritional quality of lettuce leaves, even when grown with sub-optimal P concentration.
In a second part, we compared lettuce plants (cv. Salinas) grown in soilless culture with optimal P concentration (+P/-AM), with sub optimal P concentration (-P/-AM) and with plants grown with lower P concentration (-50%) and inoculated with the AM fungus F. mosseae before transplanting (-P/+AM). The gene expression profile was analysed in both roots and leaves, and transcriptomic values were associated with physiological and biochemical parameters.
Overall, in comparison with -P/-AM plants, 3,057 genes were differentially regulated by mycorrhizal symbiosis (-P/+AM) and 2,606 genes were induced by optimal phosphate nutrition (+P/-AM). The pattern of differentially expressed genes for both effects showed major differences suggesting a context dependent regulation of genes related to photosynthesis, solute transport, metabolism of phytohormones, redox homeostasis, and transcriptional regulation.
Concerning metabolic pathways, mycorrhizal plants highlight the activation of genes involved in phenylpropanoids, carotenoids, and vitamins production. These data are coherent with the results of physiological and biochemical analyses. Transcriptomic, physiological, and biochemical data strongly support the potential of AM symbionts to act as biofertilizers for lettuce soilless cultivation with beneficial effects on both plant growth and leaf content of health promoting phytochemicals through genetic pathways largely different from those activated in plants grown with optimal P supply.
The results obtained clearly highlight that lettuces in soilless culture during symbiosis can overcome phosphorus deficiency in nutrient solution proving that arbuscular fungi can act as an effective biofertilizer increasing biomass and leaves area of a host plant and promoting the biosynthesis of health-related compounds for a balanced human diet.