美國加州卡內(nèi)基研究院的科學(xué)家與一些同事*發(fā)現(xiàn)了一種植物固醇能促使兩種基因相互對(duì)抗——一個(gè)基因抑制另一個(gè)基因從而確保水稻和實(shí)驗(yàn)植物擬南芥（Arabidopsis thaliana,，芥菜的一種親緣物種）的葉子正常生長,。這些結(jié)果發(fā)表在了2009年12月15日出版的《植物細(xì)胞》雜志上,，它對(duì)于理解如何操縱作物生長和產(chǎn)量具有重要意義,。
在植物中,，固醇水平反映了環(huán)境和內(nèi)部信號(hào)，而且控制著許多過程,。稱為油菜素內(nèi)酯（BRs）的固醇激素在細(xì)胞表面開始它們的活動(dòng),，并通過一種分子接力從而把信號(hào)送入細(xì)胞核，打開或關(guān)閉特定基因,，特別是那些調(diào)控植物生長和發(fā)育的關(guān)鍵基因,。盡管科學(xué)家對(duì)這種固醇如何影響擬南芥基因已經(jīng)有了很多發(fā)現(xiàn)，它對(duì)水稻等農(nóng)作物的影響還知之甚少,。
論文的作者之一,、卡內(nèi)基研究院植物生物學(xué)系的Zhi-Yong Wang解釋了這項(xiàng)研究：“我們知道這種固醇對(duì)于激活控制著擬南芥以及水稻的細(xì)胞生長的基因具有非常重要的作用。對(duì)這種固醇最敏感的反應(yīng)之一是水稻的葉彎曲,，這是由于葉片和葉鞘連接處的上層細(xì)胞的擴(kuò)張?jiān)斐傻?。我們希望確定這種固醇如何在水稻中發(fā)揮作用。我們發(fā)現(xiàn)了這種固醇影響兩個(gè)基因編碼（或制造）的蛋白質(zhì),，后者把其它基因打開或關(guān)閉,；它們被稱為轉(zhuǎn)錄因子。在水稻中,，當(dāng)一個(gè)稱為葉傾斜增加1基因（ILI1）被打開的時(shí)候,，它導(dǎo)致了葉彎曲。有趣的是,，我們發(fā)現(xiàn)了ILI1蛋白也與另一種稱為IBH1的轉(zhuǎn)錄因子結(jié)合,，并抑制其功能。當(dāng)存在過多ILI1蛋白的時(shí)候,，葉子過度彎曲,，讓植株變得粗濃。當(dāng)IBH1濃度高的時(shí)候,，連接處的細(xì)胞生長停滯,，而水稻變得非常直，占據(jù)的空間更少,。在正常的水稻植株中,，ILI1和IBH1的平衡讓生長得到控制。”
這一對(duì)基因提供了控制葉子角度的獨(dú)特工具,，這對(duì)于作物產(chǎn)量有重要作用,，因?yàn)橹绷⒌娜~片改善了光捕獲而且能讓水稻植株種植得更密集,，從而獲得每公頃的更高產(chǎn)量。
通過一系列實(shí)驗(yàn),，這組科學(xué)家確定了這種固醇如何與這些基因相互作用,。他們發(fā)現(xiàn)了油菜素內(nèi)酯相反地調(diào)控這些基因——ILI1被激活了，而IBH1被抑制了,。因此,，這種固醇改變了ILI1和IBH1的蛋白質(zhì)產(chǎn)物的平衡，從而啟動(dòng)了細(xì)胞生長,。
“看上去這種固醇導(dǎo)致了IBH1基因停止制造IBH1蛋白,，與此同時(shí)增加了ILI1蛋白的生產(chǎn)，而這關(guān)閉了IBH1對(duì)細(xì)胞生長的抑制,。這確保了細(xì)胞根據(jù)固醇的水平而生長到合適的長度,，”Wang評(píng)論說。
這組科學(xué)家對(duì)芥菜進(jìn)行了類似的實(shí)驗(yàn),，結(jié)果顯示出固醇與芥菜基因以同樣的方式相互作用,。“由于類似的基因在不同的植物體內(nèi)做了同樣的事情，這個(gè)過程很可能非常古老而且見于許多不同的高等植物,。我們對(duì)這類機(jī)制了解得更多,，我們就能更好地改造農(nóng)作物從而養(yǎng)活不斷增加的人口，”Wang得出結(jié)論說,。（生物谷Bioon.com）
更多水稻有關(guān)研究：
The Plant Cell：水稻microRNA的效應(yīng)復(fù)合體和靶標(biāo)
Science：水稻中鑒別出可持久抗擊稻瘟病的基因
Sci. Signal.：發(fā)現(xiàn)水稻耐淹水的關(guān)鍵基因
New Phytologist：水稻落?；虻倪M(jìn)化與馴化過程機(jī)制
Nature：觸發(fā)深水水稻中間節(jié)增長的基因
PNAS：特殊基因造成水稻雜交品種不育
The Plant Cell：揭示出水稻不定根發(fā)育的調(diào)控機(jī)理
PNAS：水稻抗旱性調(diào)控基因
生物谷推薦原始出處：
The Plant Cell December 15, 2009; 10.1105/tpc.109.070441
Antagonistic HLH/bHLH Transcription Factors Mediate Brassinosteroid Regulation of Cell Elongation and Plant Development in Rice and Arabidopsis
Li-Ying Zhang 1, Ming-Yi Bai 2, Jinxia Wu 3, Jia-Ying Zhu 1, Hao Wang 1, Zhiguo Zhang 3, Wenfei Wang 1, Yu Sun 4, Jun Zhao 1, Xuehui Sun 3, Hongjuan Yang 5, Yunyuan Xu 5, Soo-Hwan Kim 6, Shozo Fujioka 7, Wen-Hui Lin 5, Kang Chong 5, Tiegang Lu 3, and Zhi-Yong Wang 2*
1 Key Laboratory of Photosynthesis and Environmental Molecular Biology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China; Graduate School of the Chinese Academy of Sciences, Beijing 100049, China
2 Key Laboratory of Photosynthesis and Environmental Molecular Biology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China; Department of Plant Biology, Carnegie Institution for Science, Stanford, California 94305
3 Biotechnology Research Institute/National Key Facility for Gene Resources and Gene Improvement, Chinese Academy of Agricultural Sciences, Beijing 100081, China
4 Department of Plant Biology, Carnegie Institution for Science, Stanford, California 94305
5 Key Laboratory of Photosynthesis and Environmental Molecular Biology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China
6 Department of Biological Sciences, Yonsei University, Wonju-Si 220-710, Korea
7 RIKEN Advanced Science Institute, Wako-shi, Saitama 351-0198, Japan
In rice (Oryza sativa), brassinosteroids (BRs) induce cell elongation at the adaxial side of the lamina joint to promote leaf bending. We identified a rice mutant (ili1-D) showing an increased lamina inclination phenotype similar to that caused by BR treatment. The ili1-D mutant overexpresses an HLH protein homologous to Arabidopsis thaliana Paclobutrazol Resistance1 (PRE1) and the human Inhibitor of DNA binding proteins. Overexpression and RNA interference suppression of ILI1 increase and reduce, respectively, rice laminar inclination, confirming a positive role of ILI1 in leaf bending. ILI1 and PRE1 interact with basic helix-loop-helix (bHLH) protein IBH1 (ILI1 binding bHLH), whose overexpression causes erect leaf in rice and dwarfism in Arabidopsis. Overexpression of ILI1 or PRE1 increases cell elongation and suppresses dwarf phenotypes caused by overexpression of IBH1 in Arabidopsis. Thus, ILI1 and PRE1 may inactivate inhibitory bHLH transcription factors through heterodimerization. BR increases the RNA levels of ILI1 and PRE1 but represses IBH1 through the transcription factor BZR1. The spatial and temporal expression patterns support roles of ILI1 in laminar joint bending and PRE1/At IBH1 in the transition from growth of young organs to growth arrest. These results demonstrate a conserved mechanism of BR regulation of plant development through a pair of antagonizing HLH/bHLH transcription factors that act downstream of BZR1 in Arabidopsis and rice.
