Fototropin2

Fototropin2, commonly referred to as phototropin 2, is a blue-light receptor in plants. It belongs to the phototropin family of flavin-photosensors and is encoded by the PHOT2 gene in Arabidopsis thaliana. Like its homolog Fototropin1, Fototropin2 contains two LOV (Light, Oxygen, or Voltage) sensing domains at the N-terminus that bind flavin mononucleotide and a C-terminal serine/threonine kinase domain. When blue light is absorbed, a covalent adduct forms between FMN and a conserved cysteine in the LOV domains, triggering conformational changes that activate the kinase domain and propagate blue-light signaling. Phototropins are generally cytosolic but are associated with the plasma membrane upon activation.

Fototropin2 participates in several blue-light responses, including chloroplast movement, phototropic bending, and stomatal conductance. In Arabidopsis, Fototropin2 contributes to chloroplast avoidance and accumulation responses dependent on light intensity and acts in concert with Fototropin1; mutants lacking Phot2 show altered chloroplast movements and reduced sensitivity to blue light in certain tissues.

Downstream targets include NPH3 and PKS4; phosphorylation modulates movement and growth responses; interactions with other signaling components determine tissue-specific outcomes. The activity of Fototropin2 is shaped by the cellular context and light regime, linking blue-light perception to rapid physiological and developmental adjustments.

Fototropin2 signaling often occurs in redundancy with Fototropin1, yet Fototropin2 also has distinct roles in various tissues such as leaves and guard cells, where blue light triggers rapid changes in chloroplast positioning, growth orientation, and stomatal behavior.