文章的通讯作者是遗传与发育生物学研究所李云海研究员，李云海实验室博士研究生徐冉是该论文第一作者。这项研究得到了中国科学院、科技部和国家自然科学基金委的资助。

植物器官大小是重要的产量性状，器官大小不仅受环境影响，而且受到严格的遗传调控。到目前为止，对器官大小调控机制的认识甚少。

在之前的研究中，李云海研究组曾鉴定出一个种子和器官大小的调控基因DA1，它编码一个泛素受体（Control of final seed and organ size by the DA1 gene family in Arabidopsis thaliana）。在这一研究的基础上，研究人员又在da1-1突变体背景下进行诱变，筛选得到了一个da1-1的增强子（eod8-1）。eod8-1的突变发生在MED25基因中。MED25基因编码中介复合体（Mediator complex）亚基25。中介复合体是转录因子和RNA聚合酶II相互作用的桥梁，介导基因的转录调控。MED25基因的突变导致细胞扩展和细胞分裂持续时间延长从而形成大的器官，而过表达MED25引起细胞数目和细胞大小降低而形成小的器官。遗传学分析表明，MED25和DA1协同地调节细胞分裂，从而协同控制器官大小。

该项研究阐述了植物中介复合体亚基25（MED25）在器官大小调控中的作用，提出了MED25调控器官大小的分子机制，揭示了转录装置在器官大小调控中的重要作用。另外，此工作也将为提高作物产量和生物量提供理论基础。

原文摘要：

Control of final organ size by Mediator complex subunit 25 in Arabidopsis thaliana

Control of organ size by cell proliferation and cell expansion is a fundamental developmental process, but the mechanisms that establish the final size of organs and whole organisms remain elusive in plants and animals. We have previously demonstrated that DA1, which encodes a predicted ubiquitin receptor, controls the final size of seeds and organs by restricting cell proliferation in Arabidopsis. Through a genetic screen for mutations that enhance the floral organ size of da1-1, we have identified an enhancer of da1-1 (eod8-1). The eod8-1 mutation was identified, using a map-based cloning approach, in Mediator complex subunit 25 (MED25; also known as PFT1), which is involved in the transcriptional regulation of gene expression. Loss-of-function mutants in MED25 form large organs, with larger and slightly increased numbers of cells as a result of an increased period of cell proliferation and cell expansion, whereas plants overexpressing MED25 have small organs owing to decreases in both cell number and cell size. Our genetic and physiological data suggest that MED25 acts to limit cell and organ growth independently of MED25-mediated phytochrome signaling and the jasmonate pathway. Genetic analyses show that MED25 functions redundantly with DA1 to control organ growth by restricting cell proliferation. Collectively, our findings show that MED25 plays a crucial role in setting final organ size, suggesting that it constitutes an important point of regulation in plant organ size control within the transcriptional machinery.

作者简介：

李云海 男，研究员，博士生导师。

1996年河南大学学士。1999年中国水稻研究所硕士。2003年中国科学院遗传所博士。2003-2008年英国John Innes Centre博士后。研究方向是植物种子和器官大小控制的分子机理，其目标是利用模式植物拟南芥来探讨基本发育生物学问题，并将模式植物的研究结果应用到农作物中， 提高作物产量。

植物种子和器官大小控制的分子机理研究

在不同物种间，植物种子和器官大小有着显著差异，但在物种内个体之间种子和器官的大小相对一致，说明植物种子和器官的大小是受遗传控制。然而最终植物种子和器官大小调控的分子机制目前并不清楚。此外,植物种子,器官乃至个体大小的研究也是正在兴起的一个新的研究领域。我们实验室在模式植物拟南芥中系统的分离鉴定了种子和器官大小相关的突变体(da),并克隆几个种子和器官大小控制的关键基因。其中，

DA1基因编码了一个新的蛋白,能够与一个da1的增强子(EOD1)作用在平行的遗传途径,共同控制种子和器官的大小。实验室目前的主要工作是利用分子遗传,细胞生物学，生物化学和生物信息学的手段来研究DA, da1的增强子和抑制子的功能,目的在于阐明植物种子和器官大小控制的分子机理。此外,我们也正应用这些种子和器官大小控制的基因来提高作物产量和生物量。


Publications

1 Li Y*, Zheng L, Corke F, Smith C and Bevan MW*. Control of seed and organ size by the DA1 gene family in Arabidopsis thaliana. Genes and Development (In press. *Corresponding author)

2 Li Y, Smith C, Corke F, Zheng L, Merali Z, Ryden P, Derbyshire P, Waldron K and Bevan MW. Signaling from an altered cell wall to the nucleus mediates sugar-responsive growth and development in Arabidopsis thaliana. Plant Cell, 2007, 19: 2500-2515.

3 Li Y, Lee KK, Walsh S, Smith C, Hadingham S, Sorefan K, Cawley G and Bevan MW. Establishing glucose- and ABA- regulated transcription networks in Arabidopsis by microarray analysis and promoter classification using a relevance vector machine. Genome Research, 2006, 16(3):414-27.

4 Rook F, Hadingham S, Li Y and Bevan MW. Sugar and ABA response pathways and the control of gene expression. Plant Cell& Enviroment, 2006, 29 (3):426-434.

5 Li Y, Sorefan K, Hemmann G and Bevan MW. Arabidopsis NAP and PIR regulate actin-based cell morphogenesis and multiple developmental processes. Plant Physiology, 2004, 136: 3616-3627.

6 Li Y, Qian Q, Zhou Y, Yan M, Sun L, Zhang M, Fu Z, Wang Y, Han B, Pang X, Chen M and Li J. BRITTLE CULM1, which encodes a COBRA-like protein, affects the mechanical properties of rice. Plant Cell, 2003, 15:2020-2031.