fototropine

Fototropine, known in English as phototropin, is a blue-light receptor that regulates a variety of light responses in plants and some algae. It is a flavin-dependent serine/threonine kinase composed of two LOV (light, oxygen, voltage) sensing domains at the N-terminus and a C-terminal kinase region. Its chromophore is flavin mononucleotide (FMN).

Blue light activates fototropine by forming a covalent adduct between FMN and a conserved cysteine in the LOV2 domain, causing a conformational change that relieves autoinhibition and activates the kinase. The resulting autophosphorylation affects signaling partners including the NPH3/RPT family, which modulate auxin transport through PIN proteins and lead to adaptive growth responses.

In plants, fototropine mediates phototropism (growth toward light), chloroplast movement to optimize light capture, and blue-light–induced stomatal opening. It also influences leaf expansion under various light conditions. These responses help balance photosynthesis efficiency and photodamage risk.

In Arabidopsis thaliana, fototropins exist as two related genes, Phot1 and Phot2, with overlapping but distinct roles in sensing light intensity and duration. Phot1 generally governs responses at lower light levels, while Phot2 contributes at higher intensities. Homologous fototropins are found across green plants and many algae.

Fototropine signaling continues to be a model for understanding blue-light perception in plants and has potential applications in crop improvement by optimizing light-use efficiency and stress responses.