In a study published online in PNAS, the research group led by XIE Fang from Center for Excellence in Molecular Plant Science/Institute of Plant Physiology and Ecology of the Chinese Academy of Sciences revealed the molecular mechanism that nuclear envelope localized calcium channel proteins DMI1 and CNGC15 co-encode nuclear calcium signals in the signaling pathway of plant-microbe symbiosis, which provides new insights into the encoding of calcium signals during symbiosis. 

Plant establishment of endosymbiotic associations with nitrogen fixing bacteria and nutrient acquiring arbuscular mycorrhizal fungi involves induction by microbial signals, a shared plant signaling pathway which has at its core, nuclear Ca²⁺ oscillations. Such Ca²⁺ oscillations require a Ca²⁺ pump, and multiple channels (DMI1 and CNGC15s) that interact at the nuclear membrane. However, how calcium oscillations are encoded by these channels is unknown. 

This study describes a gain-of-function mutation in the cation-selective channel DMI1 of Medicago truncatula (M. truncatula) that causes spontaneous nuclear Ca²⁺ oscillations, leading to symbiotic gene expression and spontaneous nodule formation. The causative mutation sites at an interface between two RCK domains of DMI1, and additional mutations that stabilize this interface also cause spontaneous Ca²⁺ oscillations and nodulation in M. truncatula. This supports the hypothesis that structural changes associated with these RCK domains are intrinsic to the activation of the calcium channel complex.