山口淳二 教授 / YAMAGUCHI, Junji

生き物の姿は環境適応の履歴

山口淳二 教授 /  YAMAGUCHI, Junji

研究分野・テーマ・内容

研究分野 植物科学
研究テーマ 生物の環境適応戦略とその分子機構

研究内容

地表に固定したまま生きる植物は、厳しい外界の環境変化に対して、細胞・組織内の微環境を変化させることで生存を図ります。この環境適応過程は、遺伝的プログラムとともに様々の外部環境シグナル伝達が最終的に統合された結果として決定されるものです。その過程では、細胞内の物質代謝・輸送系等の内的な調節を促しながら、細胞死、成長相の転換等が進行し、最終的には植物の形さえも変化させることになります。私たちは、高等植物のみが有するこのような環境適応ダイナミズムの解明を最終目標としています。そして、その延長として、重要な遺伝子(群)を利用することで、私たち人間社会あるいは地球環境に有益な植物・作物を作り出すことを目指しています。

メッセージ

私たちは「生物の環境適応戦略」に興味があり、その研究を行っています。生物の特徴・個性はゲノムに刻まれていますので、ゲノム機能に関する研究が中心です。特に環境適応能力に優れた高等植物に着目し、これに働く遺伝子群の性質・機能の解明をめざしています。具体的には、ユビキチン・プロテアソーム機能、器官サイズ制御、植物免疫機能に関する研究を行っています。

生物学の根本的な問題は、どれも限りなく深く、魅力的です。研究に興味のある方は、まずそこから始めていくと良いと思います。

参考文献・論文・著書

nameYAMAGUCHI Junji

Research subject

Specialized field

Plant Biology and Agricultural Sciences

Key words

・Ubiquitin-proteasome system
・Environmental and high CO2 adaptation
・Metabolic and growth regulation
・Epigenetics and organ size regulation
・Biotic stress responses (Plant immunity)
・Model plants

Research subject

A. Ubiquitin-proteasome system involved in metabolic regulation and organ size regulation:

The ubiquitin-proteasome system functions to degrade short-lived regulatory proteins, to control many cellular events involved in cell cycle regulation, signal transduction, apoptosis and metabolic regulation, as well as those involved in the elimination of damaged or misfolded proteins. Proteins destined for degradation in this pathway are first modified by the covalent attachment of polyubiquitin chains, which is catalyzed by ubiquitin ligases. The ubiquitinated proteins are then recognized and degraded by the 26S proteasome, a multisubunit ATP-dependent protease with broad substrate specificity.

Plant growth and development are controlled by the concerted actions of many signaling pathways which are triggered by developmental and metabolic cues. Nutrients such as sugars and nitrogen compounds, referred to as the ‘C/N’ balance, play an important role as signaling molecules that modulate expression of many plant genes involved in diverse physiological processes, such as germination, seedling development, flowering, senescence, and pathogen responses. We demonstrated ubiquitin ligase ATL31 that functions in the C/N response inArabidopsis thaliana (ref 1). Further proteomics approaches by immunoprecipitation and MS analyses revealed that the ATL31 targets and ubiquitinates 14-3-3 proteins for degradation via the ubiquitin-proteasome system during the response to cellular C/N status [ref 2 and also see the review entitled “Carbon and nitrogen metabolism regulated by ubiquitin-proteasome system”Plant Signaling & Behavior 6: (2011) PMID: 21897122].

To further understand plant proteasome functions, we focused on the RPT2a subunit of the 26S proteasome regulatory particle. The Arabidopsis genome contains two genes, AtRPT2a andAtRPT2b, which encode paralog molecules of the RPT2 subunit. Interestingly, the rpt2a mutant showed specific phenotype of enlarged leaves caused by increased cell size, in correlation with increased ploidy. Detailed analyses revealed that cell expansion is increased in the rpt2a mutant by extended endoreduplication early in leaf development [ref 3 and also see the review entitled “How does the plant proteasome control leaf size?” Plant Signaling & Behavior 5: 1119-1120 (2010)].

B. Plant Immunity and plant-microbe interactions:

Plants respond to pathogen infection by activating a defense mechanism known as plant immunity. One of the most efficient and immediate resistance reactions against pathogen attack in plants is the hypersensitive response (HR), which leads to rapid local cell death at the site of pathogen entry that is characterized by the restricted growth and spread of the pathogen. Little is known, however, about the regulatory mechanism of programmed cell death (PCD) in plant immunity. Control of this HR-mediated PCD seems to involve the concerted action of several signaling molecules.

Lesion mimic mutants that result in constitutive misregulation of cell death are powerful tools with which to unravel the complex PCD pathway in relation to plant immune systems. To clarify new components of the negative regulation of the PCD pathway in HR, we isolated and characterized a single recessive nsl2 mutant, which has been originally reported as the cad1, having a phenotype that mimics a HR-like cell death in the absence of pathogens. The NSL2 gene encodes a protein containing a MACPF domain that is present in perforin and in complement components involved in animal innate immunity [see original paper entitled “The Arabidopsis gene CAD1 controls programmed cell death in the plant immune system and encodes a protein containing a MACPF domain” Plant Cell Physiol., 46: 902-912 (2005)]. We now attempt to clarify functions of the NSL2 on plant immunity and plant-microbe interactions (ref 4).

message

Recent work in our laboratory is focused on two areas, the function of ubiquitin proteasome system in plants (A), and on mechanisms related to plant immunity (B). We mainly use the convenient laboratory plant Arabidopsis, which allows the parallel use of classical and molecular genetics. We are also interested in studying on protein-protein interactions by yeast two-hybrid and/or immuno-coprecipitation methods as well as through proteomics approaches.

Our laboratory aims to keep active performance on research and friendship among the members (see group photo). Join us!

references

  • 1. Sato T, Maekawa S, Yasuda S, Sonoda Y, Katoh E, Ichikawa T, Nakazawa M, Seki M, Shinozaki K, Matsui M, Goto DB, Ikeda A, Yamaguchi J (2009) CNI1/ATL31, a RING type ubiquitin ligase that functions in the Carbon/Nitrogen response for growth phase transition in Arabidopsis seedlings. Plant J. 60: 852-864
  • 2. Sato T, Maekawa S, Yasuda S, Domeki Y, Sueyoshi K, Fujiwara M, Fukao Y, Goto DB, Yamaguchi J (2011) Identification of 14-3-3 proteins as a target of ATL31 ubiquitin ligase, a regulator of the C/N response in Arabidopsis thaliana. Plant J. 68: 137-146
  • 3. Sonoda Y, Sako K, Maki Y, Yamazaki N, Yamamoto H, Ikeda A, Yamaguchi J (2009) Regulation of leaf organ size by the Arabidopsis RPT2a 19S proteasome subunit. Plant J. 60: 68-78
  • 4. Asada Y, Yamamoto M, Tsutsui T, Yamaguchi J (2011) The Arabidopsis NSL2 negatively controls systemic acquired resistance via hypersensitive response. Plant Biotechnol. 28: 9-15