A mutation in a nuclear-membrane localized calcium channel enhances symbiosis

Calcium oscillations are widely employed molecular signals, but how signals are encoded and decoded remains largely unknown. In a new study, Cook et al. investigated mutations in the nuclear envelope-localized calcium channel CNGC15 from the legume Medicago truncatula. This protein normally forms a complex with a second calcium channel protein, DMI1, and together they mediate signaling between plants and endosymbiotic fungi and bacteria and induce symbiosis genes in the presence of the symbiont. The authors identified a single-amino acid mutation of CNGC15 that enables it to produce calcium oscillations independently of DMI1 and Nod-factors (signals from rhizobia symbionts); the authors describe the product of the gain-of-function mutation (CNGC15^GOF) as an autoactivated channel. Interestingly, the frequency of calcium oscillations in the GOF mutant was less than that of that of the wild-type channel. However, in the presence of DMI1 and the Nod-factor signal, the frequency was restored to its wild-type rate; thus, CNGC15^GOF produces two types of signals, the autoactivated low-frequency signal and the endosymbiont-activated high-frequency signal. Although symbiosis genes were not expressed in the CNGC15^GOF plants in the absence of the symbionts, the plants did increase the production of flavonoids, which serve as attractants to symbionts. Furthermore, the plants expressing CNGC15^GOF showed enhanced symbiosis with both arbuscular mycorrhiza and rhizobia. Finally, the authors identified wheat lines with the corresponding channel mutation and found that these lines showed significantly enhanced AM colonization, both in controlled and field conditions. These results show the low-frequency calcium oscillations generated by the autoactivated channel promote symbiosis, raising the possibility of lowering fertilizer used without losing crop productivity. (Summary by Mary Williams @PlantTeaching.bsky.social) Nature 10.1038/s41586-024-08424-7