Transmembrane kinase receptor (PubMed:1332795). Phosphorylates only serine and threonine residues (PubMed:8224199). Involved in auxin signal transduction and cell expansion and proliferation regulation (PubMed:23613767). Forms with ABP1 a cell surface auxin perception complex that activates ROP signaling pathways (PubMed:24578577). Required for auxin promotion of pavement cell interdigitation (PubMed:24578577). Auxin promotes the formation of the ABP1-TMK1 protein complex (PubMed:24578577). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Interacts (via extracellular domain) with ABP1. Expressed in roots, leaves, stems, siliques and flowers. The leucine-rich repeat (LRR) domain is disrupted by a non-LRR region, resulting in the formation of two LRR solenoid structures shaped like the Arabic number '7'. This is strikingly different from the horseshoe structures of the canonical LRR proteins. Autophosphorylated on serine and threonine residues. Glycosylated. No visible phenotype (PubMed:23613767). Tmk1 and tmk2 double mutants, tmk1 and tmk3 double mutants and tmk1, tmk2 and tmk3 triple mutants have no visible phenotypes (PubMed:23613767). Tmk1 and tmk4 double mutants, tmk1, tmk2 and tmk4 triple mutants and tmk1, tmk3 and tmk4 triple mutants have a severe reduction in organ size, a substantial delay in growth and development, and a decrease in fertility (PubMed:23613767). Tmk1, tmk2, tmk3 and tmk4 quadruple mutants are embryo lethal (PubMed:23613767, PubMed:24578577). Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.