Physiological Responses and Gene Co-Expression Network of Mycorrhizal Roots under K⁺ Deprivation

Arbuscular mycorrhizal (AM) associations enhance the phosphorous and nitrogen nutrition of host plants, but little is known about their role in potassium (K⁺) nutrition. Medicago truncatula plants were cocultured with the AM fungus Rhizophagus irregularis under high and low K⁺ regimes for 6 weeks. We determined how K⁺ deprivation affects plant development and mineral acquisition and how these negative effects are tempered by the AM colonization. The transcriptional response of AM roots under K⁺ deficiency was analyzed by whole-genome RNA sequencing. K⁺ deprivation decreased root biomass and external K⁺ uptake and modulated oxidative stress gene expression in M. truncatula roots. AM colonization induced specific transcriptional responses to K⁺ deprivation that seem to temper these negative effects. A gene network analysis revealed putative key regulators of these responses. This study confirmed that AM associations provide some tolerance to K⁺ deprivation to host plants, revealed that AM symbiosis modulates the expression of specific root genes to cope with this nutrient stress, and identified putative regulators participating in these tolerance mechanisms.