The cytokinin histidine kinase receptors regulate nodulation, shoot and root development in Pisum sativum

In this study, we expanded the understanding of cytokinin (CK) perception in legumes by generating and characterizing novel pea cytokinin receptor mutants carrying mutations for the four cytokinin histidine kinase CHK genes in pea, CHK1, CHK2, CHK3 and CHK4. We constructed single, double, triple and quadruple mutants and analyzed their shoot, root, and nodulation phenotypes. We evaluated their contributions to the activation of CK-responsive genes, TCSn promoter activity, and used RNAi knockdowns of CHK1 to explore its role in nodulation. We found key roles for CHK1 in promoting nodulation, CHK3 in delaying leaf senescence and CHK4 in promoting leaf size and axillary shoot branching. Traits such as stem elongation and width as well as shoot and root size were regulated redundantly by the CHK receptors. Overall, this work provides a genetic dissection of cytokinin receptor function in pea, advancing our understanding of hormone signaling in a crop legume and offering genetic insights with potential applications for improving both shoot architecture and symbiotic efficiency.