| Signal perception through cell surface receptors is critical for growth and development in all living organisms. In Arabidopsis, we have isolated loss-of-function mutations for the four genes comprising the TMK subfamily of receptor-like kinases (RLKs). These TMKs have a leucine-rich-repeat extracellular domain, a single transmembrane domain, and a cytoplasmic kinase domain. The quadruple mutant combination results in a severe reduction in organ size, a substantial retardation in growth, and sterility. Kinematic studies of organ growth revealed that TMKs specifically control cell growth, but not cell proliferation, in roots, hypocotyls, and stamen filaments. In leaves, however, both cell growth and cell proliferation are affected. Additionally, tmk mutant roots and hypocotyls showed reduced sensitivity to applied auxin in growth inhibition assays, lateral root induction and auxin response reporter DR5::GUS activation. Taken together with structural and biochemical evidence, members of TMK subfamily may function as an entry point to orchestrate plant growth and development by regulation of cell growth and cell proliferation downstream of auxin. |
