Membrane-localized, ECM-sensing proteins in land plant, animals, and fungi. Related membrane proteins identified in brown algae are also shown. MCA1, MIDI1-complementing activity 1; THE1, THESEUS1; FER, FERONIA; WAK, wall-associated kinase; RALF, rapid alkalinization factor; LRX, leucine-rich repeat extensin; LLG1, LORELEI-like glycosylphosphatidylinositol-anchored protein 1; FLA4, fasciclin-like arabinogalactan protein 4; COB, extracellular glycosyl-phosphatidyl inositol-(GPI)-anchored protein COBRA; FEI1/2, leucine-rich repeat receptor kinases; MIK2, MALE DISCOVERER1-interacting receptor like kinase 2 I; SUB, STRUBBELIG; BRI1, brassinosteroid insensitive 1; RLP44, receptor-like protein 44; ROP, rho of plants; ROP GEF, rho of plants guanine-nucleotide exchange factor; MPK3, map kinase 3; VI, vacuolar invertase; ACS, aminocyclopropane 1-carboxylic acid synthase HG, homogalacturonan; OGs, oligogalacturonides; XG, xyloglucan; RG-1, rhamnogalacturonan I; RG-2, rhamnogalacturonan II; ROS, reactive oxygen species; GF, growth factor; GFR, growth factor receptor; DDR2, Discoidin domain-containing receptor 2; EBPR, Elastin-binding protein receptor, ITGA/B, Integrin A/B subunit; POSTN, fasciclin domain protein periostin; Ras, Ras GTPase; JNK, c-Jun N-terminal mitogen-activated protein kinase; PI3K, Phosphoinositide 3-kinase; Akt, RAC-α serine/threonine-protein kinase; RhoA, Ras homolog A GTPase; ROCK, Rho-associated protein kinase; ERK, Extracellular-signal-regulated mitogen-activated protein kinase; WSC1, Cell wall integrity and stress response component 1; MID2, Mating pheromone-induced death protein 2; SLN1, Synthetic lethal of N-end rule 1; SHO1, Synthetic high osmolarity-sensitive 1; CCH1/MID1, Stretch-activated voltage-gated high-affinity calcium channel composed of Calcium channel homolog 1 and Mating pheromone-induced death protein 1; Rho1, Ras homolog 1 GTPase; Slt2, Suppressor of the lytic phenotype mitogen-activated protein kinase 2; Rlm1, Resistance to lethality of MKK1P386 overexpression MADS-box transcription factor 1; Ypd1, Tyrosine phosphatase dependent 1; Cdc42, Cell division cycle 42 rho-like GTPase; Hog1, High-osmolarity glycerol mitogen-activated protein kinase 1; Hot1, High-osmolarity-induced transcription factor 1; MP, mannoprotein; FAS1-like, Fasciclin-like domain protein, LRR-RKs, Leucine-rich repeat domain receptor kinases; ?, ligand unknown or uncertain step of the signal transduction pathway; black dots, calcium atoms; branched black lines indicate GPI anchors. Adapted from [26,117,118].