Research

“Paths are made by walking.”

--Franz Kafka -

Plants, which live their entire lives on the ground where they sprout, need to endure inconvenient environments without moving away. This has given plants a really sophisticated developmental and environmental response during evolution. In order to clarify the mechanisms of plant development and environmental responses, we focus our research on "keeping an eye on living cells".

Mechanism of plant organelle positioning

The plant body is composed of cells with organelles that support cellular functions (Figure A). The number of organelles is controlled by the cell and is known to be distributed in the right "place" at the right "time" depending on the differentiation state and external environment. This suggests that the arrangement of cellular organelles is important for the expression of cellular functions, but how their distribution is determined is largely unknown. We mainly use mosses (Figure B) to visualize the cytoskeleton (Figure C) and synthetic organic chemical probes (Figure D) to focus on the mechanism and function of placing the right number of organelles in the right place at the right time.

Mechanism of plant cell elongation

Plant cells maintain an intracellular pressure that pushes the cell wall outward, which is called turgor pressure. The turgor pressure plays an important role in plant cell elongation.In particular, pollen tubes and root hairs have partially soft cell walls and exhibit a mode of elongation called tip growth, in which only the apical portion of the cell elongates. In nature, it is thought that tip growing cells encounter situations where they must pass through very narrow gaps. For example, pollen tubes elongate through narrow spaces in female tissues for fertilization (Figure E), and root hairs elongate through narrow spaces in soil particles to absorb water and nutrients (Figure F).We fabricated microfluidic channels that are smaller than the cells and studied the behavior of the tip-growing cells (Figure G), and found that they are able to elongate through a gap of 1 micrometer and, in the case of moss protonemata, divide. We are now studying the mechanism of this flexible and powerful response by live cell anyalysis (Figure H).

Construction of plant hormone flow atlas

Plant hormones are involved in the development, differentiation, and growth processes of plants, as well as their responses to the external environment (Figure I). Auxin, in particular, has been predicted to exist for 140 years, and the phototropism of plant shoots toward light is explained by a polar transport model in which auxin moves in the opposite direction to light to promote cell elongation (Figure J). A lot of auxin regulators have been identified and molecular tools for auxin distribution have been developed (Figure K).However, the cell-to-cell movement of auxin itself has not yet been captured. Therefore, we developed a fluorescent auxin together with synthetic organic chemists. By directly observing the cell-to-cell movement of plant hormones, we would like to contribute to the construction of a plant hormone flow atlas (Figure L).

　　The above are just a few of our research themes. In addition to molecular biology and biochemistry experimental facilities, we have microbeam irradiators and infrared observation microscopes for photobiological analysis . We also have access to state-of-the-art imaging equipment at the Nagoya University Live Imaging Center, which I manage. In addition, we can routinely use technologies from different fields, such as microfluidic channel and synthetic chemical probes. We welcome the participation of those who are interested in the above themes, those who want to find phenomena that no one knows yet and pursue their molecular functions, and those who want to further develop your current research themes using state-of-the-art imaging technology, microfabrication technology, and organic fluorescent probes.

植物が再生力を発揮するしくみ

　植物がもつ驚異的な再生力の謎を解明しようと研究しています。卵細胞と精子（精細胞）が受精した受精卵は、分裂して特殊な役割を担う様々な分化細胞を生み出します。受精卵のように様々な分化細胞をつくることができる細胞のことを多能性幹細胞と言います。一方、特殊な役割をもつ分化細胞も、環境が整えば多能性幹細胞になることがあります。この現象はリプログラミングと呼ばれます。植物は、切り株からひこばえが生えたり（図M）、挿し木によって増えたりすることから、リプログラミングしやすいと考えられています。特に、コケ植物蘚類のヒメツリガネゴケは、桁外れに高いリプログラミング能力があります。ヒメツリガネゴケの茎葉体において（図N）、葉の細胞に分化した細胞はもう分裂しません。ところが１細胞だけ取り出すと、幹細胞になり分裂を開始します（動画N）。その後の発生過程を観続けたところ、再び葉の細胞をもつ植物個体にまで再生することがわかりました（Sato et al. 2017 Sci Rep 7 1909）。一方、隣接した2細胞を取り出した場合には、どちらか一方の細胞しか幹細胞になりません（動画P）。幹細胞化した細胞は隣接細胞の幹細胞化を抑制していると考えられますが、一体どのようなしくみが働いているのでしょうか。幹細胞化する仕組み、幹細胞化を抑える仕組みの詳細はまだまだわかっていないことばかりです。幹細胞化のしくみがわかると、植物育種上の様々な課題の解決、ひいては農作物の生産効率の向上にもつながることでしょう。そこで私達は、一細胞解析装置やAIロボット技術などを駆使して植物幹細胞の不思議の解明に取り組んでいます。

　上記は、研究テーマのごく一部です。実験室には、分子生物学実験設備、生化学実験設備の他、光反応を誘導、観察するマイクロビーム照射装置や赤外線観察顕微鏡が整備されています。また、佐藤がセンターチーフを務める名古屋大学ライブイメージングセンターの最先端イメージング機器も使用できます。さらに、微細加工技術によるマイクロ流路作成や有機合成技術による新規蛍光プローブ開発などの異分野技術を日常的に用いることができます。上記のテーマに興味のある方、まだ誰も知らない手つかずの現象を発見し分子機能までを追求したい方、現在手がけている研究テーマを最先端イメージング技術、微細加工技術、有機蛍光プローブなどを用いてさらに発展させたい方の参加も歓迎します。