Abstract

Plants have the ability to overcome nutrient limitations by establishing beneficial symbiotic associations with soil microbes. In the elaborate association between legumes and nitrogen-fixing rhizobia, the bacteria are hosted within specialized root nodules, where they have the optimal environment for fixing atmospheric dinitrogen for the plant. The success of this interaction depends on a compatible molecular dialogue between the plant and the rhizobial partner before the bacteria can enter the host root via newly formed transcellular tubular structures called infection threads (ITs). While IT development initiates from root hair cells, coordinated reprogramming in underlying root cell layers takes place for accommodating the symbiotic bacteria and initiating nodule organogenesis. Although remarkable progress has been made on the identification of key plant genes required for symbiotic signalling, much remains to be done for the understanding of how they orchestrate downstream cellular reprogramming and coordinated developmental changes. We have combined molecular, genetic and live cell imaging approaches to investigate regulatory mechanisms underlying rhizobia infection and its reprogramming in the model Medicago truncatula. Our data demonstrate the importance of intercellular communication and cell-specific remodelling for paving the way for endosymbiotic root infection.