Breaking ground: ABLs and TMKs as co-receptors to perceive extracellular auxin

Auxin is an important phytohormone that regulates a string of vital rapid responses, and its signaling perception mechanism has been one of the hot spots of research. It has been shown that the ABP1/TMKs module is involved in regulating extracellular auxin signaling, however, the role of ABP1 as an auxin receptor is highly controversial. Therefore, the mechanism of quintessential TMKs sense extracellular auxin remains unresolved. Recently, a study identified two new auxin-binding proteins, ABL1 and ABL2, which directly interact with TMKs to perceive apoplast auxin. This groundbreaking research unravels the mystery surrounding how plants perceive extracellular auxin signals.