Phototropin

Phototropin

LOV2 domain of phototropin-2 protein from Arabidopsis thaliana

Phototropin is a type of photoreceptor found in plants that is sensitive to blue light. It plays a crucial role in the process of phototropism, where plants grow towards or away from light, and is involved in various other light-mediated responses.

Structure

Phototropins are composed of two main domains: the LOV domains (Light, Oxygen, or Voltage) and the kinase domain. The LOV domains are responsible for light perception, while the kinase domain is involved in signal transduction.

LOV Domains

The LOV domains are specialized flavin-binding domains that undergo a conformational change upon absorption of blue light. This change initiates a signaling cascade that ultimately leads to physiological responses in the plant.

Kinase Domain

The kinase domain of phototropin is responsible for phosphorylating target proteins, which is a key step in the signaling pathway. This domain becomes active upon light-induced conformational changes in the LOV domains.

Function

Phototropins are primarily involved in mediating phototropic responses, where they help direct plant growth towards light sources. This is crucial for optimizing photosynthesis by maximizing light capture.

Phototropism

In phototropism, phototropins detect the direction of light and initiate a signaling cascade that results in the differential growth of plant cells. This causes the plant to bend towards the light source.

Stomatal Opening

Phototropins also play a role in the opening of stomata, which are pores on the leaf surface that regulate gas exchange. Blue light activation of phototropins leads to stomatal opening, facilitating carbon dioxide uptake for photosynthesis.

Chloroplast Movement

Another function of phototropins is to mediate the movement of chloroplasts within plant cells. In low light, chloroplasts spread out to maximize light absorption, while in high light, they move to minimize damage.

Mechanism

Upon absorption of blue light, the LOV domains undergo a structural change that activates the kinase domain. This activation leads to the phosphorylation of downstream targets, which then propagate the signal to elicit a physiological response.

Evolution

Phototropins are believed to have evolved early in the plant lineage, providing an adaptive advantage by allowing plants to efficiently utilize light for growth and development. They are conserved across various plant species, indicating their fundamental role in plant biology.

Related pages

• Photoreceptor (biology)
• Phototropism
• Blue light
• Photosynthesis