Jingfang Hao and Alizee Malnoe standing with labcoats and mouth protection in a laboratory cold room.Jingfang Hao and Alizée Malnoë are isolating the lumen of chloroplats, an important technique used in the recently published article, in the cold room (photo: Robert Calderon).

Plants need light but too much of it can be harmful. A recent study, led by Alizée Malnoë from UPSC and Umeå University and by Mei Li from the Chinese Academy of Sciences, sheds light into the mechanism on how plants protect themselves from excess of light.

Jingfang Hao, postdoc at UPSC and shared first author of the study, says that the photoprotection they studied here is a biological process named non-photochemical quenching (NPQ), which plants carry out to dissipate the excess absorbed light as heat under strong illumination.

"The negative regulation of this photoprotection is mediated by a chloroplast membrane-anchored protein, SUPPRESSOR OF QUENCHING 1 (SOQ1). SOQ1 consists of a stromal domain, transmembrane domain and lumenal domain containing thioredoxin-like (Trx-like), NHL domain and C-terminal domain (CTD)", says Jingfang Hao and continues:

"The previous study determined that Trx-like domain is essential for SOQ1 suppression function on photoprotection. We discovered that besides Trx-like domain, CTD is indispensable for the negative regulation of photoprotection. The mechanism is that CTD can accept the electron from Trx-like domain and donate the electron to inhibit the target protein required for NPQ".

Why is this an important finding?

"Because this is the first study to report the crystal structure of SOQ1 lumenal domain and determine the function of the C-terminal domain of SOQ1 protein. Our findings uncover a new mechanism that how plants protect themselves from strong illumination".

Jingfang Hao tells further that investigating the localization of SOQ1, she isolated the chloroplast sub-fractions such as intact thylakoids, thylakoid membranes and lumen.

"I was surprised to find SOQ1 can be cleaved as several truncated forms in the lumenal fraction. Our Chinese colleagues also found these truncated forms when they purified the SOQ1 lumenal domains from bacteria. These findings suggest that the truncated forms could play some physiological functions".

What use will your findings have?

"The structure of the SOQ1 lumenal domain can provide a reference for the researchers to study similar proteins or proteins containing similar domains in other species. Moreover, our findings give a contribution to understanding how plants adapt the stressful environments".White cake with the SOQ1 and a very simplified form of the model described in the paper on it in colourTo celebrate the article, Jingfang got a cake from her colleagues illustrating their new findings (photo: Robert Calderon).

The article

Yu G#, Hao J#, Pan X#, Shi L, Zhang Y, Wang J, Fan H, Xiao Y, Yang F, Lou J, Chang W, Malnoë A*, Li M*. Structure of Arabidopsis SOQ1 lumenal region unveils C-terminal domain essential for negative regulation of photoprotective qH. Nat. Plants. 2022 Jul;8(7):840-855. https://doi.org/10.1038/s41477-022-01177-z

More about SOQ1
Alizée Malnoë and her group are working on photoprotection in plants. To know how plants get rid of excess light energy so that they do not get sunburned is interesting for biological research in general. It is particularly important to know because the amount of light absorbed by plants depends on the amount of CO2 fixed by photosynthesis and therefore determines how much biomass is produced.
SOQ1 is a protein in the leaves that manages the amount of light absorbed. Previously, only the part T and N of this molecular machine were known. In the study, the researchers identified the new part C of this machine and now they are able to understand how it works. SOQ1 has been found to have similarities to a bacterial protein which is known to transfer electrons between the different parts and thus changes the activity of other proteins. The researchers hypothesize that the same thing is happening in the leaf of plants and they are now working on finding the target protein of SOQ1 and how it modifies it exactly.
Not only bacteria and plants but also humans and animals have a version of SOQ1 which when mutated reduces the lifespan to only two short years. The researchers hope that their plant biology research can help to understand the function of SOQ1 in humans and tell more about the neurodegenerative disease in which it is implicated. It is a rare disease whose English acronym is FINCA, or syndrome of fibrosis-neurodegeneration-cerebral angiomatosis. Thanks to plant research, it is also known that SOQ1 acts on a protein, whose human counterpart is involved in Alzheimer's disease. However, the researchers think that it will take them much longer to determine if SOQ1 plays a role in Alzheimer's disease, too.

For questions, please contact:

Alizée Malnoë
Umeå Plant Science Centre
Department of Plant Physiology
Umeå University
Email: This email address is being protected from spambots. You need JavaScript enabled to view it.

Jingfang Hao
Umeå Plant Science Centre
Department of Plant Physiology
Umeå University
Email: This email address is being protected from spambots. You need JavaScript enabled to view it.

Text: Per Melander, Jingfang Hao