E. DEPARTMENT OF INTEGRATED GENETICS
E-d. Division of Applied Genetics - Takashi Araki Group

RESEARCH ACTIVITIES

(1) Physiological roles of chromatin assembly factor-1 in epigenetic control of meristem activity during post-embryonic development in plants

Takashi Araki^{1, 2}, Mitsutomo Abe^{1, 3}, Hidetaka Kaya⁴ and Kei-ichi Shibahara (¹Graduate School of Science, Kyoto University, ²Japan Science and Technology Agency, ³PROBRAIN, ⁴Genome & Drug Research Center, Tokyo University of Science)

--Loss-of-function mutants of chromatin assembly factor-1 (CAF-1) in Arabidopsis, fasciata (fas), show a wide variety of morphological abnormalities and unique defects in the expression of WUSCHEL and SCARECROW genes in meristems (Cell 104, 131-142. 2001). We found that transcriptional gene silencing (TGS) of endogenous CACTA transposons was released in a stochastic manner in fas, without decreasing global levels of DNA methylation. Other endogenous silent genes at different chromosomal sites, a DNA transposon AtMu1 and a hypothetical gene T5L23.26 at a heterochromatin knob, were also transcriptionally activated. Activation of the three different silent loci occurred non-concomitantly to each other. Furthermore, TGS of a silent β-glucuronidase (GUS) transgene was also de-repressed randomly in fas plants, without apparent correlation with developmental abnormalities. Activated state of GUS was maintained during growth to produce clusters of cells expressing GUS. Based on these observations, we propose a model that CAF-1 contributes to the stable inheritance of epigenetic states through multiple rounds of cell divisions. Defect of CAF-1 function explains the stochastic occurrence of pleiotropic morphological phenotypes observed in fas mutants (Ogawa, Kaya, and others, submitted). We also investigated other genes involved in epigenetic control of meristem activity, such as BRUSHY1 (BRU1)¹ and ANTI-SILENCING FUNCTION1 (ASF1) (in preparation).

(2) Genes involved in the integration of various genetic pathways for regulation of the floral transition

Takashi Araki^{1, 2}, Mitsutomo Abe^{1, 3}, Sumiko Yamamoto^{1, 2}, Yasufumi Daimon¹, Ayako Yamaguchi¹, Yoko Ikeda¹, Michitaka Notaguchi¹ and Masaki Kobayashi¹ (¹Graduate School of Science, Kyoto University, ²Japan Science and Technology Agency, ³PROBRAIN)

--Floral transition in Arabidopsis is regulated by several pathways which converge on the transcriptional regulation of floral pathway integrators including FT. FT is a direct target of CO and encodes a protein with similarity to mammalian proteins (PEBP/RKIP) involved in cellular signaling. FT transcription is immediately induced in cotyledon and leaf vascular tissues upon transfer from short-day to inductive long-day photoperiods. Promotion of flowering by FT requires the activity of another flowering-time gene FD which encodes a bZIP transcription factor preferentially expressed in the shoot apex. FD is involved in transcriptional activation of the floral meristem identity genes AP1 and CAL redundantly with LFY. ft; lfy and fd; lfy double mutants are very similar in severe reduction of AP1 mRNA levels and strong defects in floral specification. Loss of FT function suppresses ectopic up-regulation of AP1 in seedlings by FD over-expression. Mutant forms of FD which lack a C-terminal potential phosphorylation site cannot interact with FT in yeast cells and fail to complement fd late-flowering phenotype even by over-expression. These and other evidences suggest that FT and FD are inter-dependent in promotion of floral transition and activation of AP1 expression (in preparation). Since the activity of FD, which is preferentially expressed in shoot apex, seems to require protein/protein interaction with FT, shoot apex is likely the site of action of FT protein. Consistent with this, restoration of FT function in whole region or outermost layer (L1) of the shoot apex can rescue ft late-flowering. These raise an interesting possibility that the FT protein may represent a long-distance signal generated in photoperiodically-induced leaves (mainly in vascular tissues) and act at the shoot apex to initiate floral development. Arabidopsis genome has a homolog of FT, called TWIN SISTER OF FT (TSF). We found that TSF acts redundantly with FT as a floral pathway integrator (Yamaguchi et al., submitted).

PUBLICATIONS

Papers
1. Takeda, S., Tadele, Z., Hofmann, I., Probst, A.V., Angelis, K.J., Kaya, H., Araki, T., Mengiste, T., Scheid, O.M., Shibahara, K., Scheel, D. and Paszkowski, J. (2004). BRU1, a novel link between responses to DNA damage and epigenetic gene silencing in Arabidopsis. Genes Dev 18, 782-93.

Reviews
2. 荒木崇（2004）“花成を制御する遺伝因子と環境因子の相互作用",『植物の環境応答と形態形成のクロストーク』,岩渕雅樹・篠崎一雄（編）,シュプリンガー・フェアラーク東京,pp.57-63.

Books
3. 荒木崇（2004）“第24章 花成の調節",『Taiz & Zeiger植物生理学 第三版』,島崎研一郎・西谷和彦（監訳）,培風館,pp.568-601.

ORAL PRESENTATIONS

1. Araki, T., Yamamoto, S., Daimon, Y., Yamaguchi, A., Ikeda, Y., Ichinoki, H., Notaguchi, M., Goto, K. and Abe, M. FLOWERING LOCUS T: a link between photoperiodic induction in leaves and evocation at shoot apex in Arabidopsis. (invited lecture) 18th International Conference on Plant Growth Substances, Canberra, September, 2004.
2. 阿部光知、山本純子、大門靖史、山口礼子、池田陽子、櫟木春理、野田口理孝、荒木崇「シロイヌナズナ花芽分化誘導統御過程の遺伝子制御」第45回日本植物生理学会年会シンポジウム「花芽分化誘導の制御機構解明」、八王子市、2004年3月
3. 池田陽子、小林恭士、阿部光知、荒木崇「GL2型ホメオボックス遺伝子FWAを用いた花成制御の解析」第45回日本植物生理学会年会、八王子市、2004年3月
4. 山口礼子、小林恭士、山本純子、阿部光知、荒木崇「花成遺伝子FTの相同遺伝子TSFの解析」第45回日本植物生理学会年会、八王子市、2004年3月
5. 山本純子、阿部光知、櫟木春理、小林恭士、荒木崇「シロイヌナズナの遺伝子FDによる花芽分裂組織遺伝子AP1の発現制御」第45回日本植物生理学会年会、八王子市、2004年3月
6. 遠藤求、中村賢志、荒木崇、頼光花、増村威宏、田中國介、望月伸悦、長谷あきら「子葉葉肉細胞で発現させたフィトクロムB-GFPによるFT遺伝子を介した花成制御」第45回日本植物生理学会年会、八王子市、2004年3月
7. 荒木崇「生殖開始サイズの遺伝制御メカニズム」基礎生物学研究所・共同利用研究研究会「オオバコの生物学:その現代的見直し」、岡崎市、2004年7月
8. 阿部光知、山本純子、小林恭士、大門靖史、荒木崇「シロイヌナズナ花成遺伝子FDの機能解析」日本植物学会第68回大会、藤沢市、2004年9月
9. 池田陽子、阿部光知、荒木崇「GL2型ホメオボックス遺伝子FWAによる花成阻害機構の解析」日本植物学会第68回大会、藤沢市、2004年9月
10. 野田口理孝、阿部光知、荒木崇「FT過剰発現による花成促進効果の接木伝達性に関する研究」日本植物学会第68回大会、藤沢市、2004年9月
11. 山口礼子、小林恭士、山本純子、阿部光知、荒木崇「花成制御におけるFT相同遺伝子TSFの機能解析」日本植物学会第68回大会、藤沢市、2004年9月
12. 荒木崇「FT―葉における光周性花成誘導と茎頂における花芽分裂組織形成のリンク―」科研費特定領域研究「植物自家不和合性」公開シンポジウム『植物の生殖研究―その最前線と今後の方向―』、東京都文京区、2004年11月

POSTER PRESENTATIONS

1. Daimon, Y., Yamamoto, S., Abe, M., Yamaguchi, A., Ikeda, Y., Ichinoki, H., Notaguchi, M., Goto, K. and Araki, T., FLOWERING LOCUS T: a link between photoperiodic induction in leaves and evocation at shoot apex in Arabidopsis.
15th International Conference on Arabidopsis Research, Berlin, July, 2004.
2. Ikeda, Y., Abe, M. and Araki, T. Moleculer basis of late-flowering phenotype in dominant fwa mutants.
15th International Conference on Arabidopsis Research, Berlin, July, 2004.
3. Yamaguchi, A., Kobayashi, Y., Yamamoto, S., Abe, M. and Araki, T. Characterization of TSF, a homolog of flORAL PRESENTATIONS pathway integrator FT.
15th International Conference on Arabidopsis Research, Berlin, July, 2004.
4. 遠藤朋子、赤松昌彦、島田武彦、小林恭士、荒木崇、藤井浩、清水徳朗、大村三男「CiFT導入カラタチ系統間における生育特性の解析」日本園芸学会平成16年度春季大会、宇都宮市、2004年4月

EDUCATION

1. 荒木崇 京都大学大学院理学研究科・理学部（兼担）助教授
2. 荒木崇 近畿大学農学部集中講義,2004年4-5月
3. 荒木崇 筑波大学遺伝子実験センターセミナー,2004年11月

SOCIAL CONTRIBUTIONS AND OTHERS

1. 荒木崇 2004年（第11回）日本植物生理学会論文賞（共同受賞）
2. 荒木崇 Plant and Cell Physiology (editorial board)
3. 荒木崇 日本植物生理学会（評議員）
4. 荒木崇 岡山県生物科学総合研究所所外研究協力員
5. 荒木崇 特定非営利活動法人『シニア自然大学』の地球環境大学講座（代表:河野昭一京都大学名誉教授）講師,2004年4-10月