Phototropiner

Phototropiner is a term used in some scientific literature to denote blue-light receptor proteins of the phototropin family that mediate blue-light responses in plants and algae. The more widely used name for these proteins is phototropin; phototropiner is sometimes considered an alternative or historical label. Phototropins act as blue-light receptors that trigger signaling pathways leading to various light-dependent responses.

Phototropins are serine/threonine kinases with two N-terminal LOV (light, oxygen, voltage) domains that bind flavin mononucleotide as a chromophore. In blue light, a conserved cysteine within the LOV domains forms a covalent adduct with FMN, triggering a conformational change that relieves autoinhibition and activates the kinase domain. This initiates downstream signaling through phosphorylation of target proteins, including members of the NPH3 family and related components, shaping the light response.

In plants, phototropins regulate phototropic bending toward light and chloroplast movement to optimize light capture or minimize photo-damage. They also influence stomatal opening in response to blue light and can affect leaf positioning and other growth responses under varying light conditions. The precise outcomes depend on light intensity, duration, and the tissue context.

Localization and signaling involve association with the plasma membrane and dynamic redistribution in response to light, integrating with auxin signaling, cytoskeletal changes, and other blue-light–driven processes. Phototropins thus serve as central nodes in blue-light perception and coordinate multiple adaptive responses.

Evolutionarily, phototropin genes are found across green algae and land plants, with multiple paralogs in many species that exhibit overlapping but distinct functional roles. In model species such as Arabidopsis thaliana, phot1 and phot2 represent primary phototropin isoforms with complementary functions. See also: Phototropin, LOV domain, NPH3, phototropism.