Project description:Legumes produce specialized root nodules that are distinct from lateral roots in morphology and function, with nodules intracellularly hosting nitrogen-fixing bacteria. We have previously shown that a lateral root program underpins nodule initiation, but there must be additional developmental regulators that confer nodule identity. Here, we show two members of the LIGHT SENSITIVE SHORT HYPOCOTYL (LSH) transcription factor family, predominantly known to define shoot meristem complexity and organ boundaries, function as regulators of nodule organ identity. In parallel to the root initiation program, LSH1/LSH2 recruit a program into the root cortex that mediates the divergence into nodules, in particular with cell divisions in the mid cortex. This includes regulation of auxin and cytokinin, promotion of NODULE ROOT1/2 and Nuclear Factor Y-A1 and suppression of the lateral root program. A principal outcome of LSH1/LSH2 function is the production of cells able to accommodate nitrogen-fixing bacteria, a key feature unique to nodules.
Project description:Medicago truncatula engages in root nodule symbiosis by developing a de novo plant organ (known as nodule) in its roots in response to the infection by rhizobia. These nodules are de novo plant organs that provide an optimal environment for the rhizobia to fix nitrogen in exchange for photosynthates. The establishment of root nodule symbioses (RNS) requires the coordination of two distinct processes: bacterial infection and nodule organogenesis. In this study we used single-cell RNA-seq to investigate the first hours of the establishment of the root nodule symbiosis aiming to identify the transcriptional mechanisms governing this process.
Project description:Legumes grow specialized root nodules that are distinct from lateral roots in morphology and function, with nodules intracellularly hosting beneficial nitrogen-fixing bacteria that provide the plant with nitrogen. We have previously shown that a lateral root-like program underpins nodule initiation, but there must be additional developmental programs that confer nodule identity. Here, we show that two members of the LIGHT SENSITIVE SHORT HYPOCOTYL (LSH) transcription factor family, known to define organ boundaries and meristem complexity in the shoot, function as regulators of nodule organ identity. LSH1/LSH2 function upstream of and together with the known nodule regulators Nuclear Factor Y A1 and NODULE ROOT1/2. The principal outcome of LSH1/LSH2 function is the production of cells able to accommodate nitrogen-fixing bacteria, a unique nodule feature. We conclude that the coordinate recruitment of a pre-existing shoot developmental program, in parallel to a root program, underpins the divergence between lateral roots and nodules.
