Report on the Study of Diatom Phytochromes Integrating Underwater Light Spectrum to Sense Depth

Academic Background

The distribution of light in marine ecosystems profoundly influences aquatic life. Light not only attenuates with depth but also undergoes significant spectral changes. However, research on how phytoplankton perceive these light changes through photoreceptors remains insufficient. Diatoms, as crucial marine phytoplankton, play a significant role in understanding the light adaptation strategies of marine ecosystems. Phytochromes are proteins primarily sensing red ® and far-red (FR) light, widely present in photosynthetic and non-photosynthetic organisms. However, in marine environments, red and far-red light are strongly absorbed by water, leaving the functional mechanisms of diatom phytochromes (DPh) in such environments a mystery.

This study aims to reveal the light perception mechanisms of DPh in marine environments by integrating functional studies and environmental surveys, particularly how DPh perceives underwater spectral changes to modulate physiological functions.

Source of the Paper

The research was conducted by multiple institutions from France, Italy, and the United States, with primary authors including Carole Duchêne, Jean-Pierre Bouly, and Juan José Pierella Karlusich. The research team is affiliated with the French National Centre for Scientific Research (CNRS), Sorbonne University, and the Stazione Zoologica Anton Dohrn in Italy, among others. The paper was published online on October 29, 2024, in the journal Nature.

Research Process and Results

1. Distribution and Functional Studies of Diatom Phytochromes

The study first investigated the global distribution of diatoms containing DPh using environmental sequence data from the Tara Oceans project. The results showed that DPh genes are primarily distributed in regions above 30° absolute latitude, especially in high-latitude areas with significant seasonal mixed-layer depth variations. This suggests that DPh may have adaptive value in coping with vertical displacements in the water column.

To further study the light perception properties of DPh, the research team developed an in vivo dose-response assay in the model diatom species Phaeodactylum tricornutum, triggering photoreversible responses mediated by DPh through spectral changes. The experiments demonstrated that DPh can trigger photoreversible responses across the entire light spectrum, particularly under simulated deep-sea low-blue-light conditions, where DPh regulates photosynthetic acclimation.

2. Spectral Properties and Light Responses of DPh

The research team determined the absorption spectra of recombinant DPh proteins. The results showed that DPh proteins have maximal absorption peaks in the far-red (767 nm) and red (680 nm) regions, with minor peaks in the blue (423 nm and 383 nm) regions. These spectral properties indicate that the light perception features of DPh are conserved across different environments.

To further investigate the light response properties of DPh, the research team constructed a DPh response reporter system in P. tricornutum, quantifying DPh responses through the expression of yellow fluorescent protein (YFP). The experiments showed that DPh can induce YFP expression under far-red and near-infrared (NIR) light, and it can also trigger light responses under blue light. Additionally, DPh responses are photoreversible, with red, green, and blue light all capable of reversing NIR-induced responses.

3. Modeling DPh Light Responses in Marine Environments

To simulate DPh light responses in marine environments, the research team developed a model based on the photochemical properties of DPh. The model predicts that DPh light responses increase with depth, particularly in deep-water regions dominated by blue and green light. This finding suggests that DPh can decode optical depth information by perceiving spectral changes, providing cells with information about their vertical position in the water column.

4. The Role of DPh in Photosynthetic Acclimation

To assess the functional role of DPh in diatom physiology, the research team constructed DPh knockout mutants (tpdph) in Thalassiosira pseudonana. The experiments showed that under simulated deep-sea low-blue-light conditions, the photosynthetic performance of tpdph mutants significantly decreased, particularly in terms of maximal electron transport rate (ETRmax) and light saturation point (Ek). This indicates that DPh plays a crucial role in the photosynthetic acclimation of diatoms, especially in low-light environments.

Conclusions and Significance

By integrating functional studies and environmental surveys, this study reveals the light perception mechanisms of diatom phytochromes in marine environments. The results demonstrate that DPh can perceive light changes across the entire spectrum, decode optical depth information, and modulate diatom physiological functions. This discovery provides new insights into how marine phytoplankton adapt to underwater light environments and offers an important theoretical foundation for future marine ecological research.

Research Highlights

1. Broad-Spectrum Light Perception by Phytochromes: DPh can perceive not only red and far-red light but also trigger light responses under blue and green light, showcasing its broad-spectrum perception capabilities in marine environments.
2. Optical Depth Sensing: By perceiving spectral changes, DPh can decode optical depth information, providing cells with information about their vertical position in the water column.
3. Photosynthetic Acclimation: DPh regulates photosynthetic acclimation in diatoms under low-light conditions, particularly in deep-sea environments where its function is crucial.
4. Global Distribution Pattern: The distribution of DPh genes in high-latitude regions is closely related to their adaptive role in seasonal mixed-layer depth variations, highlighting their importance in coping with vertical displacements in the water column.

Other Valuable Information

The study also provides detailed data on the photochemical properties of DPh, including its absorption spectra and light response curves, offering important references for future photoreceptor research. Additionally, the DPh response reporter system and light response models developed by the research team provide new experimental tools and theoretical frameworks for similar studies.

Through this research, we have deepened our understanding of the light perception mechanisms in diatoms and opened new directions for studying light adaptation strategies in marine ecosystems.