Research

Research Focus ー What makes plants the best chemists on Earth?

Plants produce a diverse array of organic compounds using CO₂ as a solo carbon source through photosynthesis and central carbon metabolism. These carbon energy metabolic pathways (e.g., carbon fixation, respiration, and biosynthesis of essential carbohydrates, such as sugars and amino acids) play indispensable roles in cellular energy homeostasis and promote plant growth and adaptation. In the face of ongoing climate change, however, various abiotic stresses, such as drought and temperature, have been implicated as a common thread that downregulates plant carbon energy metabolism, resulting in reduced plant growth and crop productivity. In particular, we still have limited knowledge of how these carbon energy pathways are regulated and respond to various stresses to maintain plant performance. This knowledge gap has been a bottleneck in metabolic engineering for our sustainable society to ensure crop productivity under challenging climatic conditions. My long-term goals are to elucidate the regulatory mechanisms of plant carbon energy metabolism and to utilize these basic findings to improve plant growth and performance even under various stress conditions.

Currently, I am focusing on the following three research topics and also working on several other projects, including collaborations with scientists around the world.

Aromatic amino acid metabolism

Aromatic amino acids, L-tyrosine, L-phenylalanine, and L-tryptophan, are not only three of the twenty proteogenic amino acids but also play a crucial role as precursors of diverse aromatic natural products. These aromatic amino acid-derived compounds are essential for plant development and adaptation but also important for our daily lives as nutrition, pharmaceuticals, and biomaterials. Since 30% of photosynthetically fixed carbon is directed into the aromatic amino acid biosynthetic pathway, 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase (DHS) reaction, the first step of aromatic amino acid biosynthesis that is connected with the Calvin-Benson-Bassham cycle, is critical to control the carbon flux into the aromatic amino acid pathway (Yokoyama et al., Plant Cell, 2021, Yokoyama and Oliveira et al., 2022, Science Advances). Combining enzyme biochemistry and genetics with metabolomics, I am focusing on how aromatic amino acid biosynthesis is connected to the upstream central carbon metabolism and the downstream aromatic natural product pathways in plants.

Regulation of photosynthetic carbon metabolism

Photosynthesis harnesses solar energy to fix CO₂ into a variety of organic compounds such as sugars and amino acids. Because its performance directly determines plant growth and crop productivity, enhancing photosynthetic carbon fixation activity is anticipated to be a promising approach to sustaining the world's food supply and sequestering atmospheric CO₂ in plant tissues. Unfortunately, photosynthetic carbon fixation can be down-regulated by various environmental stresses such as drought and heat, resulting in reduced plant growth and crop productivity. Therefore, genetic engineering that maintains photosynthetic efficiency under challenging stress conditions has been desired to cope with ongoing climate change. Combining plant genetics, molecular biology, and photosynthetic measurement with metabolomics approach including stable and radioactive carbon isotope labeling, this project aims to define the regulatory mechanism underpinning the carbon fixation pathway and to examine the signaling cascade that determines plant growth in model plants and crop species.

The role of anthocyanin homeostasis in plant adaptation

Anthocyanin is a red/purple pigment that has been known for a long time to play a protective role as antioxidants in various stress responses. The core structure of anthocyanin is produced from phenylalanine, followed by many chemical modifications including glycosylation. Because of its nutritional benefit to human health, the anthocyanin biosynthetic pathway is fully examined in model plants and various horticultural species with great potential as a target of metabolic engineering. In this project, the new role of anthocyanin in plant adaptation against abiotic stresses is examined using enzyme biochemistry, genetics, and metabolomics in model and horticultural plants.

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