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.
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