控制植物器官大小的分子机理

植物器官大小是植物形态的一个重要特征并受严格的遗传调控。器官大小与两个不同的过程有关：细胞扩张和细胞分裂。分子遗传分析已经鉴定了许多基因,这些基因通过作用于其中一个或两个过程来影响器官的最终大小。某种植物个体间器官大小的差异是由控制该器官特征的基因表达水平变化引起的,通过拟南芥的遗传分析显示这些基因是如何受控制或被修饰的。以上这些资料阐明了植物如何确定继续或停止生长,同时也提供了改变植物积累生物量的方法。     

花器官大小调控机制的研究进展

自然界中植物花的大小受到遗传因素和环境因素的双重调节。传粉者、天敌和逆境胁迫等多种因素相互制约,作为选择压力共同影响花器官形态和繁殖能力,通过选择适合的基因型,推动花器官大小的进化。近年来,对花器官大小调控机制的研究又有新的进展,已在模式植物拟南芥中分离出大量参与花器官大小调控的基因,并证实它们主要在细胞水平影响花器官的增殖和生长。本文介绍花器官大小的进化及其生物学意义,并综述了拟南芥花器官大小调控机制的研究进展。     

拟南芥YUAN1基因调控器官形状和大小

器官形状和大小的控制是一个基本的发育生物学过程, 受细胞分裂和细胞扩展的影响。到目前为止, 人们对植物器官形状和大小的调控机制知之甚少。本实验室前期研究发现了一个种子和器官大小的调控基因DA1, 其编码一个泛素受体。在拟南芥(Arabidopsis thaliana)中, DA1通过抑制细胞的分裂来限制种子和器官的大小。本研究通过激活标签的方法在da1-1突变体背景下筛选到一个叶子形状发生改变的半显性突变体(yuan1-1D)。yuan1-1D形成短而圆的叶片和短的叶柄, 细胞学分析显示, 叶片和叶柄变短的主要原因是细胞的长向扩展降低导致的。YUAN1编码一个含有PHD锌指结构域的蛋白。GFP-YUAN1融合蛋白定位在细胞核内。过量表达YUAN1基因导致叶片和叶柄变短。遗传学分析显示, YUAN1和DA1、ROT3以及ROT4在控制叶片形状和大小方面作用于不同的遗传途径中。因此, 本研究鉴定了一个新的控制器官形状和大小的基因YUAN1, 为阐明植物器官形状和大小调控的分子机制提供了重要线索。     

植物MicroRNA功能的研究进展

MicroRNA(miRNA)是真核生物基因表达的一类负调控因子,植物miRNA主要在转录水平上通过介导靶基因的甲基化、在转录后水平介导靶mRNA的切割或降低靶mRNA的翻译来调节基因的表达,从而调控植物器官的形态建成、生长发育、激素分泌与信号转导以及植物对逆境胁迫因素的应答能力。该文主要综述了近年来植物miRNA在植物生长发育、激素调节与信号转导以及逆境胁迫应答中的重要作用,并针对miRNA的网络调控特征提出了今后miRNA功能研究的方向。     

光、糖与激素影响植物花色素苷合成与积累的研究进展(综述)

次生代谢物质花色素苷存在于植物的叶片、花、果实和种子的表皮细胞的液泡中,是一类使这些器官呈现从红色到黑色等系列颜色的水溶性色素。其合成过程不仅受到基因的调控,还受多种因素影响。首先是光通过信号转导途径直接或间接地调节相关酶基因表达的过程;其次是糖,常与光相互作用协调控制花着色;激素也是影响花色素苷合成的一个重要因素,往往通过影响植物体内的代谢过程和植物基因的表达来影响花色素苷的合成和积累。本文综述近20年来该领域的研究进展。     

拟南芥QUA1基因在光信号途径中的表达与功能分析

光信号在植物生长发育过程中具有非常重要的作用。不同的光信号通过调节植物下游基因的表达,进而影响细胞分化、结构和功能的改变,以及组织和器官的形成,参与植物光形态建成。QUA1 (QUASIMODO1)是拟南芥糖基转移酶家族中的一个成员,参与植物细胞壁中果胶的合成。本文以拟南芥qua1-1/cry1以及qua1-1/phyB双突变体为材料,对QUA1基因在光信号途径中的功能进行了分析。结果显示,qua1-1突变体在暗、蓝光、红光以及远红外光培养条件下下胚轴的伸长均受到抑制,QUA1基因的表达同样受到光信号的调节,而且突变体中多种光信号调节基因的表达也受到了影响。通过对qua1-1突变体下胚轴的观察发现,突变体下胚轴表皮细胞长度明显变短。与cry1以及phyB突变体相比,qua1-1/cry1和qua1-1/phyB双突变体下胚轴长度明显变短,而且双突变体中光信号调节基因的表达也有明显变化,表明QUA1可能参与了CRY1以及PHYB介导的蓝光及红光信号传导。以上结果表明QUA1影响了下胚轴细胞的伸长以及光信号调节基因的表达,并参与调控多种光信号传导途径。     

microRNA在植物生长发育中的研究进展

microRNA(miRNA)是一类广泛存在于植物体内,长约20-25个核苷酸的内源性非编码小分子RNA,通过定向降解靶基因mRNA和抑制其翻译,从而在转录后水平控制靶向基因的表达来调控多种多样的生物功能,包括植物的生长发育、生殖和对逆境胁迫的响应。已有的研究表明,miRNA及其靶基因不仅在植物的时序转换中是一个关键调控因子,也在茎尖发育、叶形态建成、花器官发育和开花时间等过程中发挥着重要调控作用。重点介绍mi RNA在调控植物生长发育过程以及发育可塑性过程中的研究进展,并对植物miRNA研究中有待进一步阐明的问题进行了探讨和展望,以期为深入解析miRNA在调节植物组织和器官模式中的功能,以及植物形态多样性中的作用和分子调控网络提供参考。     

miR319在植物器官发育中的调控作用

microRNAs(miRNAs)是一类内源性的、21~25个碱基长度的小分子非编码RNA,它通过指导剪切或者抑制翻译等方式调节植物基因的表达,参与调控植物生长发育各个方面。大量研究表明,miR319通过靶向TCPs转录因子控制植物叶、花等器官的生长命运,并参与调控部分激素生物合成和信号传导通路,在植物发育过程中发挥重要生物学功能。文章综述了miR319在植物叶形态建成、生长发育以及叶衰老和花器官发育等过程中的重要调控作用。     

伴胞细胞中表达的组蛋白脱甲基化酶感受发育信号调控开花时间

开花是高等植物发育过程中一个非常重要的转化过程,它能够保证植物的正常发育和后代的延续,并且有重要的农业价值和观赏价值[1]．开花时间的调控是一个非常复杂的过程,受到自身发育信号和外部环境因素的共同影响[2-3]．FLC是拟南芥开花调节过程中的中心抑制因子,其在拟南芥顶端分生组织和叶片维管束的伴胞细胞中均有表达,并且这两个部位的FLC对开花时间都有重要的调节作用[4]．目前已知的多数影响开花的通路都通过调节顶端FLC的表达来调控植物开花时间,关于伴胞细胞中的FLC如何被调控的研究还非常少[1, 3]． 在动植物中都存在一类具有JmjC结构域的蛋白质,是一类保守的组蛋白脱甲基化酶[5]．我们实验室最近的工作表明,JMJ18是一个受植物自身发育调节的H3K4脱甲基化酶,JMJ18主要在伴胞细胞中表达,通过特异调节伴胞细胞中的FLC调控植物开花时间[6]． Yang等[6]实验证实在体外全长的JMJ18可以特异性地以H3K4m3的多肽为底物,脱掉其上一个甲基生成H3K4m2．在拟南芥中,JMJ18主要在伴胞细胞中表达,并且表达水平受到植物自身发育进程的调控[4]．JMJ18功能缺失突变体呈现弱的晚花表型,而JMJ18的超表达植株呈现明显的早花表型,说明JMJ18参与了拟南芥开花时间的调控[4].尽管多个具有JmjC结构域的组蛋白脱甲基化酶,如 JMJ14、ELF6/JMJ11、REF6/JMJ12等都参与了拟南芥开花时间的调节,但是机制都不太清楚[5, 7],并且目前没有发现可以直接调控FLC的JmjC蛋白．Yang等的实验证实JMJ18可以结合到FLC的染色质上,通过降低FLC的染色质H3K4m3和H3K4m2修饰抑制FLC表达．FLC表达水平的降低导致FT表达的释放,促进FT在伴胞细胞中积累．积累的FT从伴胞细胞进入筛管组织,进而运输到顶端分生组织,与顶端分生组织特异性表达的bZIP转录因子FD直接相互作用,通过调节下游基因SOC1和AP1调控植物开花进程(图1)． 最近的研究发现,植物开花时间除了受到春化作用、自主途径、光周期途径、GA途径等调控以外,还可以通过自身年龄衡量因子miR156和其靶基因SQUAMOSA PROMOTER BINDING-LIKE (SPLs)调节开花进程[8]．Yang等实验证实：JMJ18主要在韧皮部的伴胞细胞表达．并且同miR156类似,在植物营养生长时期,JMJ18随着发育进程的深入表达水平逐渐升高．SUC2启动子驱动JMJ18在维管伴胞细胞中表达时也出现早花表型并且依赖于FT．这些研究结果表明,同miR156类似,JMJ18受植物自身发育调节,也可能作为自身年龄衡量因子调控植物开花时间,不同点是JMJ18是通过组蛋白修饰直接调节FLC表达调控开花时间的自身年龄衡量因子．即可能有两条感受自身年龄的途径：miR156-SPLs和JMJ18-FLC/MAFs途径,让人感兴趣的是两个因子都是表观遗传调控因子,而且在每个途径中均是前者负调控后者,而且后者均为一个转录因子基因家族,这两个途径最后都调控FT表达．这两个途径之间的关系也是一个有待于研究的科学问题,这可能会对于我们理解自身年龄衡量因子在植物开花进程中的作用有一定的启示．     

植物细胞一氧化氮信号转导研究进展

一氧化氮（nitric oxide,NO）作为重要的信号分子,调控植物的种子萌发、根形态建成和花器官发生等许多生长发育过程,并参与气孔运动的调节以及植物对多种非生物胁迫和病原体侵染的应答过程。已经知道,精氨酸依赖的NOS途径和亚硝酸盐依赖的NR途径是植物细胞NO产生的主要酶促合成途径。NO及其衍生物能够直接修饰底物蛋白的金属基团、半胱氨酸和酪氨酸残基,通过金属亚硝基化、巯基亚硝基化和Tyr．硝基化等化学修饰方式,调节靶蛋白的活性,并影响cGMP和Ca2＋信使系统等下游信号途径,调控相应的生理过程。最新的一些研究结果也显示,MAPK级联系统与NO信号转导途径之间存在复杂的交叉调控。此外,作为活跃的小分子信号,NO和活性氧相互依赖并相互影响,共同介导了植物的胁迫应答和激素响应过程。文章综述了植物NO信号转导研究领域中一些新的研究进展,对NO与活性氧信号途径间的交叉作用等也作了简要介绍。     

Cell number counts - The fw2.2 and CNR genes and implications for controlling plant fruit and organ size

Two key determinants of plant and organ size are cell number and cell size, and altering either one may affect the plant organ size, but cell number control often plays a predominant role in natural populations. Domesticated crops usually have larger fruit and harvested organ sizes than wild progenitors. Crop yields have increased significantly by breeding, often via heterosis, which is associated with increased plant and organ size primarily achieved by cell number increases. A small class of genes is now known that control plant and organ sizes though cell number or cell size. The fw2.2 gene was found to control a major QTL for tomato fruit size by negatively affecting cell numbers. Orthologs to these fw2.2 genes underlie QTLs for fruit sizes in other species, and their expression can be negatively correlated with increased cell number. In maize decreased or increased expression of the fw2.2 ortholog ZmCNR1, increases or decreases cell number, respectively, thereby affecting maize organ size throughout the plant and thus also whole plant size. Therefore, these genes should now be considered as more general regulators of plant cell number and organ size. The exact molecular function of these transmembrane domain proteins remains unknown, as does any clear relationship to the cell cycle. Because these genes control organ sizes in diverse plants and important crop species, and because they can affect whole plant size, interest arose into how effects of such genes could parallel agronomic crop improvements, in particular that by heterosis, as it also affects cell number. In joining these subjects here in discussion we speculate on how single gene cell number regulation and heterosis may cooperate in crop improvement.     

XIAO is involved in the control of organ size by contributing to the regulation of signaling and homeostasis of brassinosteroids and cell cycling in rice

Organ size is determined by cell number and size, and involves two fundamental processes: cell proliferation and cell expansion. Although several plant hormones are known to play critical roles in shaping organ size by regulating the cell cycle, it is not known whether brassinosteroids (BRs) are also involved in regulating cell division. Here we identified a rice T-DNA insertion mutant for organ size, referred to as xiao, that displays dwarfism and erect leaves, typical BR-related phenotypes, together with reduced seed setting. XIAO is predicted to encode an LRR kinase. The small stature of the xiao mutant resulted from reduced organ sizes due to decreased cell numbers resulting from reduced cell division rate, as supported by the observed co-expression of XIAO with a number of genes involved in cell cycling. The xiao mutant displayed a tissue-specific enhanced BR response and greatly reduced BR contents at the whole-plant level. These results indicated that XIAO is a regulator of BR signaling and cell division. Thus, XIAO may provide a possible connection between BRs and cell-cycle regulation in controlling organ growth.     

EBP1 regulates organ size through cell growth and proliferation in plants

Plant organ size shows remarkable uniformity within species indicating strong endogenous control. We have identified a plant growth regulatory gene, functionally and structurally homologous to human EBP1. Plant EBP1 levels are tightly regulated; gene expression is highest in developing organs and correlates with genes involved in ribosome biogenesis and function. EBP1 protein is stabilised by auxin. Elevating or decreasing EBP1 levels in transgenic plants results in a dose-dependent increase or reduction in organ growth, respectively. During early stages of organ development, EBP1 promotes cell proliferation, influences cell-size threshold for division and shortens the period of meristematic activity. In postmitotic cells, it enhances cell expansion. EBP1 is required for expression of cell cycle genes; CyclinD3;1, ribonucleotide reductase 2 and the cyclin-dependent kinase B1;1. The regulation of these genes by EBP1 is dose and auxin dependent and might rely on the effect of EBP1 to reduce RBR1 protein level. We argue that EBP1 is a conserved, dose-dependent regulator of cell growth that is connected to meristematic competence and cell proliferation via regulation of RBR1 level.     

Flower-specific expression of the Agrobacterium tumefaciens isopentenyltransferase gene results in radial expansion of floral organs in Petunia hybrida

Biotechnology has the potential to modify commercially important traits of crops, such as fruit size and stress tolerance. To date, the floricultural industry has not profited significantly from these possibilities to manipulate, for example, flower size. Cytokinins are known to be involved in many aspects of plant development, including cell division. Increasing the amount of cytokinins has the potential to increase the size of an organ, such as the flower or the fruit. The Agrobacterium tumefaciens cytokinin biosynthesis gene isopentenyltransferase ( ipt ) has been shown to increase cytokinin levels when introduced into plants. Moreover, it has a dramatic effect on the vegetative development of plants. The expression of the ipt gene under the control of the flower-specific Arabidopsis APETALA3 promoter in petunia ( Petunia hybrida ) increases the flower size dramatically, but with no effect on vegetative development. The resulting transgenic plants produced flowers with larger corolla diameter and greater total floral fresh weight. This strategy has the potential for use in the production of ornamental crops with large flowers and crop species with larger fruit.     

Conserved mechanisms regulate outgrowth in zebrafish fins

Regulation of size is one of the fundamental problems in biology. One general strategy has been to identify molecules required for cell growth and cell proliferation within an organ. This has been particularly revealing, identifying cell-autonomous pathways involved in cell growth, survival and proliferation. In order to identify pathways regulating overall limb growth and morphology, experiments have evaluated gene expression, transplanted and removed tissues, and knocked out genes. This work has provided a vast amount of information identifying molecular mechanisms regulating limb axis formation, outgrowth, and pattern formation. Using the zebrafish fin, genetic, cellular and molecular strategies have also been employed to follow both normal patterns of fin growth and growth in fin mutants. This review will focus on cellular and molecular regulation of the outgrowth and patterning of the zebrafish caudal fin during regeneration, and will emphasize similarities to other systems. Future perspectives describe opportunities using the zebrafish fin to reveal mechanisms underlying the regulation of final size.     

The mutants compacta ?hnlich, Nitida and Grandiflora define developmental compartments and a compensation mechanism in floral development in Antirrhinum majus

In order to improve our understanding of floral size control we characterised three mutants of Antirrhinum majus with different macroscopic floral phenotypes. The recessive mutant compacta ?hnlich has smaller flowers affected mainly in petal lobe expansion, the dominant mutant Grandiflora has overall larger organs, whilst the semidominant mutation Nitida exhibits smaller flowers in a dose-dependent manner. We developed a cell map in order to establish the cellular phenotypes of the mutants. Changes in organ size were both organ- and region-specific. Nitida and compacta ?hnlich affected cell expansion in proximal and distal petal regions, respectively, suggesting differential regulation between petal lobe regions. Although petal size was smaller in compacta ?hnlich than in wild type, conical cells were significantly bigger, suggesting a compensation mechanism involved in petal development. Grandiflora had larger cells in petals and increased cell division in stamens and styles, suggesting a relationship between genes controlling organ size and organ identity. The level of ploidy in petals of Grandiflora and coan was found to be equivalent to wild type petals and leaves, ruling out an excess of growth via endoreduplication. We discuss our results in terms of current models about control of lateral organ size.