Editorial: Plant-rhizobia symbiosis and nitrogen fixation in legumes

Plant-rhizobia symbiosis and nitrogen fixation in legumesNitrogen (N) is essential for life, but eukaryotes lack the ability to access this element, as only prokaryotic enzymes can convert N to ammonia.The Haber-Bosch process revolutionized agriculture by enabling synthetic N-fertilizer production, but its overuse and mismanagement created significant environmental challenges (Rockstrom et al., 2009;Richardson et al., 2023).Biological Nitrogen Fixation (BNF) by diazotrophic bacteria and symbiotic nitrogen fixation (SNF) by N-fixing plants offer age-old solutions to the N-problem (Adams et al., 2018).In this context, legumes represent a valuable biological resource to migrate into a sustainable agriculture, since in N-deficient soil, they engage in symbiosis with rhizobia.In the rhizosphere, nodulation factors (NFs) secreted by rhizobia prompt mitotic activity in the root cortex cells, triggering de-differentiation and nodule formation.Concurrently, rhizobia invade root hair cells, guided by plant-derived infection threads (ITs), towards dividing plant cells.Once inside, rhizobia are endocytosed and become enclosed by plant membrane leading to the formation of 'symbiosomes', where they multiply and function as nitrogen-fixing entities.This Research Topic encompasses eleven articles addressing both bacterial and plant aspects essential for SNF (Kang et al., 2016;Roy et al., 2020), and the agronomical benefits of this mutualistic association. LegumesIt is estimated that around 25% of nodulating legumes employ an alternative rhizobial colonization process, called intercellular infection, where bacteria invade the host plant between the epidermal cells or by crack entry (Quilbe et al., 2022).Since the molecular basis of this mechanism is largely unknown, Garcıá-Soto et al. conducted a large-scale mutant screening to discover genes recruited in the intercellular symbiotic colonization of the Frontiers in Plant Science frontiersin.