phot2

Phototropin 2, commonly abbreviated Phot2, is a Blue-light receptor protein in plants, best characterized in Arabidopsis thaliana. It belongs to the phototropin family, which also includes Phot1. Phot2 is a large cytosolic serine/threonine kinase that contains two N-terminal LOV (Light, Oxygen, Voltage) sensing domains and a C-terminal kinase domain. The LOV domains bind flavin mononucleotide (FMN) and undergo a light-induced conformational change that activates the kinase activity of Phot2.

Activation and signaling involve blue-light–induced formation of a signaling state in the LOV domains, followed by autophosphorylation and transmission of signals to downstream components. Phot2 interacts with adaptor proteins such as NPH3 and related family members, which link the receptor to auxin transport pathways and cytoskeletal dynamics. This signaling modulates several blue-light responses, including phototropism, chloroplast relocation, and stomatal behavior, via regulation of auxin distribution and intracellular organization.

Biological roles for Phot2 include mediating phototropic bending toward blue light, particularly at certain light intensities, and regulating chloroplast movement to optimize light capture or minimize photooxidative damage. It also contributes to blue-light–dependent stomatal opening and leaf morphology under specific environmental conditions. In many plants, Phot2 operates alongside Phot1, with overlapping and distinct tissue- and intensity-dependent effects. Genetic studies show that phot2 loss-of-function mutants have defects in blue-light responses, and double mutants lacking both Phot1 and Phot2 exhibit severely reduced phototropism and chloroplast movements.

Evolutionarily, Phot2 is conserved across many plant lineages, with homologs identified in angiosperms and other photosynthetic groups. The gene and its signaling pathway remain subjects of study for understanding plant light perception and optimization of light use in crops.