PHOT1

Phototropin 1 (Phot1) is a blue-light receptor and serine/threonine kinase in plants, belonging to the phototropin family that also includes Phototropin 2 (Phot2). It is encoded by genes present in many plant species, with Arabidopsis thaliana serving as a widely studied model. Phot1 proteins feature two N-terminal LOV (light, oxygen, voltage) domains that bind flavin mononucleotide (FMN) as a chromophore, and a C-terminal kinase domain. Upon blue-light absorption by FMN in the LOV2 domain, Phot1 undergoes a conformational change and autophosphorylation, initiating signaling that regulates several light-responsive processes.

Phot1 mediates phototropism toward blue light, particularly at low to moderate light intensities, by influencing auxin transport and growth curvature. It also governs chloroplast movement: in weak blue light, chloroplasts accumulate to maximize light capture, while in stronger blue light they relocate to reduce photodamage. Phot1 contributes to blue-light–induced stomatal opening and to adjustments in leaf orientation and expansion that optimize photosynthesis.

In signaling, Phot1 interacts with NPH3 and other components to modulate cytoskeletal organization and vesicle trafficking, aligning cellular growth with the light environment. Phot1 and Phot2 have overlapping functions but can contribute differently depending on light intensity and tissue type; mutants lacking both phototropins exhibit strong impairment of blue-light responses.

Evolutionarily, phototropins are conserved across many green plants and some algae, reflecting their central role in adapting growth and physiology to ambient light.