The symbiotic role of the actin filament cytoskeleton

Legumes interact with soil-borne bacteria (rhizobia), thus developing a symbiotic association that allows atmospheric nitrogen fixation inside specialized plant organs called root nodules (Gage, 2004). Root nodule colonization requires the remodeling of plant cells, which develop a novel intracellular compartment where symbionts can be hosted: the symbiotic interface. This remodeling occurs in all colonized cells, starting from the epidermal root hairs, where bacteria enter the so-called infection thread (Fournier et al., 2008; 2015), a membrane-bound tube that channels rhizobia through the root cortex, into nodule primordia and within the internal tissues of mature nodules. While several studies have investigated plant cell responses during rhizobia uptake in outer root tissues, the study of bacterial release in the deep nodule tissues is far more challenging.