Genotype-Specific Modulation of Drought Tolerance by Arbuscular Mycorrhizal Symbiosis in Foxtail Millet

Drought stress is a major environmental factor limiting crop productivity. Arbuscular mycorrhizal fungi (AMF), as beneficial soil microbes, can improve plant growth and stress resilience; however, the effectiveness of this symbiosis is often influenced by the host plant's genetic background. In this study, we investigated the interaction between AM symbiosis and drought tolerance in two foxtail millet (Setaria italica) genotypes with contrasting drought responses: the drought-tolerant ISE42 and the drought-sensitive TT8. Following a 14-day drought treatment, both genotypes exhibited wilting, but only AMF-colonized ISE42 plants recovered upon rewatering. Transcriptomic analysis revealed that AM symbiosis significantly enhanced the expression of genes involved in nitrogen transport, assimilation, lignin metabolism, and cellulose biosynthesis in ISE42, but not in TT8. These molecular changes suggest improved nutrient uptake and cell wall reinforcement as key mechanisms underlying enhanced drought tolerance. Additionally, stress hormone signaling pathways were downregulated in colonized ISE42 roots, indicating possible alleviation of drought-induced stress through AM symbiosis. Our results demonstrate genotype-specific effects of AMF on drought tolerance and highlight the importance of considering host genetic variation in the application of AMF for crop improvement. RNA-seq profiling of drought tolerant and sensitive foxtail millet accessions in response to arbuscular mycorrhizal symbiosis under drought