phototropinen

Phototropins, sometimes written phototropinen in some languages, are a family of blue-light receptor kinases that regulate light-dependent responses in plants. In Arabidopsis thaliana, the best-characterized members are phot1 and phot2, which act as primary blue-light receptors. Each phototropin contains two N-terminal LOV (Light, Oxygen, or Voltage) sensing domains that bind a flavin chromophore, followed by a C-terminal serine/threonine kinase domain. The chromophore FMN enables blue-light sensing.

Mechanism: In darkness, phototropins adopt an autoinhibited conformation. Exposure to blue light induces the formation of a covalent adduct between FMN and a conserved cysteine in the LOV2 domain, triggering a conformational change that relieves autoinhibition and activates the kinase domain. Activated phototropins phosphorylate downstream targets, integrating into signaling networks that regulate cytoskeletal organization, vesicle trafficking, and ion flux.

Physiological responses: Phototropins control phototropism, the bending of shoots toward light, and chloroplast movement within leaf cells, which shifts between accumulation under low light and avoidance under strong light. Blue light also promotes stomatal opening in guard cells, aiding gas exchange. In general, Phot1 mainly governs phototropic responses at lower light intensities, while Phot2 contributes under higher blue light and participates in chloroplast movement and stomatal signaling.

Distribution and evolution: Phototropins are conserved across green plants, including mosses, ferns, gymnosperms, and angiosperms, typically as two paralogs. The LOV-based sensing module is a common feature of various photoreceptors, reflecting diversification across plant lineages.

Applications: The LOV domains of phototropins have been utilized in optogenetics and synthetic biology as reversible, blue-light–responsive modules, enabling precise control of protein activity in diverse systems.