Lotus Shaggy-like Kinase 1 is required to suppress nodulation in Lotus japonicus.

Glycogen Synthase Kinase/Shaggy-like kinases (SKs) are a highly conserved family of signaling proteins that participate in many developmental, cell-differentiation, and metabolic signaling pathways in plants and animals. Here, we investigate the involvement of SKs in legume nodulation, a process requiring integration of multiple signaling pathways. We describe a group of SKs in the model legume Lotus japonicus (LSKs), two of which respond to inoculation with the symbiotic nitrogen-fixing bacterium Mesorhizobium loti. RNAi-knockdown plants and an insertion-mutant for one of these genes, LSK1, display increased nodulation. Ηairy root lines overexpressing LSK1 form only marginally fewer mature nodules compared to controls. The expression levels of genes involved in auto-regulation of nodulation (AON) mechanism are affected in LSK1 knockdown plants, both at early and late stages of nodulation at low nitrate levels. At higher levels of nitrate, these same plants show the opposite expression pattern of AON-related genes and lose the hypernodulation phenotype. Our findings reveal an additional role for the versatile Shaggy-like kinase gene family in integrating the signaling pathways governing legume nodulation and pave the way for further study of their functions in legumes. This article is protected by copyright. All rights reserved.