Short- and long-distance control of root development by LjHAR1 during the juvenile stage of Lotus japonicus

The autoregulation of nodulation (AON) is a universal mechanism to legumes to control the extent of nodulation via a systemic circuit and if genetically altered, as in the Lotus japonicus har1-1 mutant, leads to hypernodulation and aberrant root development. Increased nodulation of har1-1 is associated with pleiotropic effects both in the absence and presence of the symbiosis. We used two different grafting techniques to investigate the control of the non-symbiotic retarded root growth phenotype of har1-1, and demonstrate that altered root growth in the non-symbiotic condition is controlled by the genotype of both the shoot and the root. Based on these results and on the Gresshoff and Delves [Plant genetic approaches to symbiotic nodulation and nitrogen fixation in legumes. Plant Gene Res 1986;3:159–206] AON model, we propose an advanced working model for control of root development by LjHAR1.