Photosynthesis under Low Temperature Conditions

Light damages plants at low temperatures

We often think plants would be happier with more light. This is not the case for plants under low temperature or drought conditions. Under these conditions, plants cannot maintain the photosynthetic machinery in chloroplasts, which ultimately leads to the destruction of leaf cell structure. The light-induced damages affect the life cycle of plants in many ways. For example, they affect the regeneration patterns of northern forests, which was suggested by Hara and his coworkers (Homma et al., 2003). Researchers think that plants adopt several strategies to avoid light damages, but our understanding on these strategies is still limited.


Figure 1. The strategies of plants to avoid light-induced damages need to be investigated.

Tanaka showed that evergreen plants efficiently dissipate excess light energy as heat in wintertime (Tanaka 2007). This strategy appears to be highly efficient. Researchers speculate that certain chloroplast proteins are involved in this mechanism. It is hypothesized that a protein called "light-harvesting-like (LIL) proteins" is involved in this mechanism. This hypothesis is based on the results of a large-scale analysis of gene expression with an evergreen tree, which shows a drastic increase in the gene expression of a LIL protein in wintertime (Ukaji and Hara, unpublished results).

Functional analysis of LIL proteins will provide better insight in the strategies of plants to avoid damages at low temperatures


Figure 2. A protein complex comprising LIL3 and geranylgeranyl reductase (GGR) is essential for the biosynthesis of phytyl-diphosphate (PDP), that is the precursor of chlorophyll, tocopherol and phylloquinone.

LIL proteins refer to a group of chloroplast proteins that are not involved in photosynthetic reactions, but still contain an evolutionary conserved amino acid sequence that is termed the light-harvesting-complex (LHC) motif. (Originally, this motif was found in a light-harvesting protein.) Researchers in the Institute of Low Temperature Science discovered that one type of LIL protein, LIL3, is essential in the biosynthesis of various metabolites including chlorophyll and tocopherol (Tanaka et al., 2010, Takahashi et al., 2014).

Evidence shows that other LIL proteins are involved in the regulation or maintenance of photosynthesis. LIL8, participates the regulation of light harvesting (Fristedt et al., 2014, Kato et al., unpublished). LIL2 appears to be important for the maintenance of photosynthesis (unpublished results). It is likely that other LIL proteins are also involved in the maintenance and/or the regulation of photosynthesis. The goal of this project is to better understand the strategies of plants to maintain photosynthesis at low temperatures through the functional analysis of LIL proteins. We will analyze those strategies both in the model plant, Arabidopsis and evergreen trees. We are also aiming to contribute to better understanding of the ecology of the trees in cold regions.

The technology to analyze the function of chloroplast proteins/ the technology to analyze photosynthesis


Figure 3. A large-scale analysis of
protein complexes by BN-PAGE and LC-MS.

We have established a technology to analyze and identify a large number of protein complexes, which is based on the blue-native polyacrylamide gel electrophoresis and mass spectrometry (Takabayashi et al., 2013). We have used this technique for the analysis of protein complexes in various photosynthetic organisms including a land plant, Arabidopsis and a cyanobacterium, Synechocystis (http://pcomdb.lowtem.hokudai.ac.jp). In addition, we routinely analyze various photosynthetic pigments using HPLC. Prof. Akimoto (Kobe University) and Dr. Makio Yokono are able to analyze the photosynthetic reactions as fast as femto- or pico seconds. Combining these technologies with conventional techniques for the protein purification and analysis, we will analyze the function of chloroplast proteins and photosynthesis at low temperatures.

References

Project Members

Dr. Ryouichi TANAKAInstitute of Low Temperature Science, Associate Professor
Prof. Toshihiko HARAInstitute of Low Temperature Science, Professor
Dr. Kiyomi ONOInstitute of Low Temperature Science, Assistant Professor
Dr. Atsushi TAKABAYASHIInstitute of Low Temperature Science, Assistant Professor
Yukako KATOInstitute of Low Temperature Science, Technical Assistant
Dr. Seiji AKIMOTOKobe University, Associate Professor
Dr. Fumiyoshi MYOUGARIKEN, Research Scientist

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