KAI2-KL signalling regulates root hair elongation under magnesium deficiency by activating auxin, ethylene, and nitric oxide biosynthesis and signalling genes

Root hair elongation (RHL), which expands the absorptive surface area of the root, is a crucial adaptation in plants for survival under magnesium (Mg) deficient soil. Despite the significance of this trait, the molecular mechanism in Mg starvation regulating RHL is elusive. We demonstrated that karrikins regulate RHL under a limited supply of Mg via crosstalk with auxin, ethylene, and NO. We used KAI2 -KL-signalling mutants, auxin, ethylene, and NO-related genes mutants Arabidopsis and pharmacological method to investigate the role of KAI2 -KL-signalling, and its interaction with ethylene, auxin, and NO in the process of RHL in Mg deficient conditions. Mg deficiency could not enhance RHL in KAI2 -KL-signalling mutants such as kai2 and max2 Arabidopsis. Interestingly, exogenous application of ethylene, nitric oxide, or auxin recovered RHL of kai2 and max2 Arabidopsis under Mg deficiency. In contrast, exogenous supplementation of KAR 1 could not rescue RHL in auxin, ethylene, and NO-related mutants Arabidopsis . In conclusion, we suggest that karrikins signalling might regulate the RHL in response to low Mg by acting as an upstream signalling pathway of auxin, ethylene, and NO signalling.