组蛋白乙酰化/去乙酰化与基因表达调控

组蛋白是真核生物染色质的主要成分,组蛋白修饰(如甲基化、乙酰化、磷酸化、泛素化等)在真核生物基因表达调控中发挥着重要的作用.在这些修饰中,组蛋白乙酰化/去乙酰化尤为重要.组蛋白乙酰化/去乙酰化可通过改变染色质周围电荷或参与染色质构型重建而影响基因表达;更重要的是组蛋白乙酰化/去乙酰化可形成一种特殊的“密码”,被其它蛋白质识别,影响多种蛋白质因子的活动或与其相互作用,参与到基因表达调控的整个网络中.     

Antagonistic Regulation of Flowering Time through Distinct Regulatory Subunits of Protein Phosphatase 2A

Protein phosphatase 2A (PP2A) consists of three types of subunits: a catalytic(C), a scaffolding (A), and a regulatory (B) subunit. In Arabidopsisthaliana and other organisms the regulatory Bsubunits are divided into at least three non-related groups, B55, B’ and B″.Flowering time in plants mutated in B55 or B''genes were investigated in this work. The PP2A-b55α andPP2A-b55β (knockout) lines showed earlier flowering thanWT, whereas a PP2A-b’γ (knockdown) line showed late flowering.Average advancements of flowering in PP2A-b55 mutants were 3.4days in continuous light, 6.6 days in 12 h days, and 8.2 days in 8 h days.Average delays in the PP2A-b’γ mutant line were 7.1 days in 16h days and 4.7 days in 8 h days. Expression of marker genes of geneticallydistinct flowering pathways (CO, FLC, MYB33, SPL3), and thefloral integrator (FT, SOC1) were tested in WT, pp2a mutants,and two known flowering time mutants elf6 andedm2. The results are compatible with B55 acting at and/ordownstream of the floral integrator, in a non-identified pathway. B’γ was involved in repression of FLC, the mainflowering repressor gene. For B’γ the results are consistentwith the subunit being a component in the major autonomous flowering pathway. Inconclusion PP2A is both a positive and negative regulator of flowering time,depending on the type of regulatory subunit involved.     

组蛋白乙酰化／去乙酰化作用与真核基因转录调控

核小体组蛋白的翻译后修饰是真核基因转录调控中的关键步骤。对于组蛋白的这类修饰方式 ,近年来研究最为活跃的是组蛋白Ｎ末端区域保守的Ｌｙｓ上ε ＮＨ 3 的乙酰化作用。随着各种组蛋白乙酰化酶 /去乙酰化酶被克隆、鉴定 ,组蛋白乙酰化 /去乙酰化作用与真核基因转录调控之间的关系也开始逐步得以阐明。1 .真核转录相关的组蛋白乙酰化酶和组蛋白去乙酰化酶1 .1　组蛋白乙酰化酶 (ｈｉｓｔｏｎｅａｃｅｔｙｌｔｒａｎｓ ｆｅｒａｓｅ ,ＨＡＴ)　　核小体组蛋白中Ｎ末端区域上保守的Ｌｙｓ的乙酰化是染色质具有转录活性的标志之一。在组蛋白…     

成花素FT的调控运输及生理功能的研究进展

开花作为植物从营养生长到生殖生长的转折点,受外界环境变化影响,对植物发育和繁殖有着至关重要的作用。成花素(flowering locus T FT)蛋白作为拟南芥开花信号核心分子,在开花调控中扮演重要角色。拟南芥叶片在感应外界温度光照等因素变化后,通过生理钟(constants,CO)等蛋白及部分Mico-RNA正负协调调控筛管伴胞中的FT基因表达,FT蛋白通过筛管从叶片运输到茎顶端分生组织后,与一个碱性亮氨酸拉链(basic leucine zipper,b ZIP)蛋白FD结合调控茎顶端分生组织(shoot apical meristem,SAM)中的花组织形成相关基因表达,继而诱导开花。对近年来FT基因在叶片中的调控、FT蛋白的运输及其在顶端分生组织中的开花诱导机理进行综述,为进一步完善FT表达调控及功能研究提供参考。     

Regulation of Flowering Time by MicroRNAs

The shoot apical meristem (SAM) continuously produces lateral organs in plants.Based on the identity of the lateral organs,the life cycle of a plant can be divided into two phases:vegetative and reproductive.The SAM produces leaves during the vegetative phase,whereas it gives rise to flowers in the reproductive phase (reviewed in Poethig,2003).The floral transition,namely the switch from vegetative to reproductive growth,is controlled by diverse endogenous and exogenous cues such as age,hormones,photoperiod,and temperature (reviewed in B(a)urle and Dean,2006;Srikanth and Schmid,2011;Andres and Coupland,2012).The model annual Arabidopsis thaliana has been extensively used for the dissection of the molecular mechanism underlying the floral transition during the last two decades.The molecular and genetic analyses have revealed five flowering time pathways,including age,autonomous,gibberellins (GAs),photoperiod and vernalization (reviewed in Amasino and Michaels,2010).Growing lines of evidence indicate that there are extensive crosstalks,feedback or feed-forward loops between the components within these pathways,and that these multiple floral inductive cues are integrated into a set of floral promoting MADS-box genes including APETALA 1 (AP1),SUPPRESSOR OF OVEREXPRESSION OF CO 1 (SOC1),FRUITFULL (FUL) and LEAFY (LFY) (Amasino and Michaels,2010;Lee and Lee,2010;Srikanth and Schmid,2011).     

Functional and Evolutionary Characterization of the CONSTANS Gene Family in Short-Day Photoperiodic Flowering in Soybean

CONSTANS (CO) plays a central role in photoperiodic flowering control of plants. However, much remains unknown about the function of the CO gene family in soybean and the molecular mechanisms underlying short-day photoperiodic flowering of soybean. We identified 26 CO homologs (GmCOLs) in the soybean genome, many of them previously unreported. Phylogenic analysis classified GmCOLs into three clades conserved among flowering plants. Two homeologous pairs in Clade I, GmCOL1a/GmCOL1b and GmCOL2a/GmCOL2b, showed the highest sequence similarity to Arabidopsis CO. The mRNA abundance of GmCOL1a and GmCOL1b exhibited a strong diurnal rhythm under flowering-inductive short days and peaked at dawn, which coincided with the rise of GmFT5a expression. In contrast, the mRNA abundance of GmCOL2a and GmCOL2b was extremely low. Our transgenic study demonstrated that GmCOL1a, GmCOL1b, GmCOL2a and GmCOL2b fully complemented the late flowering effect of the co-1 mutant in Arabidopsis. Together, these results indicate that GmCOL1a and GmCOL1b are potential inducers of flowering in soybean. Our data also indicate rapid regulatory divergence between GmCOL1a/GmCOL1b and GmCOL2a/GmCOL2b but conservation of their protein function. Dynamic evolution of GmCOL regulatory mechanisms may underlie the evolution of photoperiodic signaling in soybean.     

Photoperiodic Regulation of Flowering in Cowpeas (Vigna unguiculata (L.) Walp.)

To test the proposition that photoperiodic controls synchronizethe flowering of cowpeas, Vigna unguiculata (L.) Walp. [V. sinensis(L.) Savi], the day-length requirements for floral initiationand for flowering were investigated in several short-day accessions.No evidence was found of different critical photoperiods atdifferent stages of development, but exposure to only 2–4short days was required for floral initiation compared withabout 20 for development to open flowers. Pod setting was increasedafter exposure to even one short day more than the number requiredfor flower opening. Floral buds at higher nodes appeared to require fewer shortdays for development to flowering than buds at the lower nodes,and displayed faster rates of development. Inflorescence budsdid not resume development if they were exposed to 15 or morelong days following inflorescence initiation. Thus, any tendencytowards synchronous flowering in cowpeas is not due to the criticalday-length for flower development being shorter than that forflower initiation, but could be the result of cumulative photoperiodicinduction of plants and the more rapid development of later-formedflowers. Vigna unguiculata (L.) Walp., cowpeas, flower initiation, flower development, fruit set, photoperiodism     

拟南芥开花时间调控的分子基础

在合适的时间开花对大多数植物的生存和成功繁衍极为重要。开花时间受错综复杂的环境因素和植物自身的遗传因子影响,由开花调控因子所构成的光周期、春化、温度、赤霉素、自主以及年龄等至少6条既相互独立又相互联系的遗传途径调控。该文综述了有关拟南芥(Arabidopsis thaliana)开花时间调控的分子机制的最新研究进展,并对今后的研究进行了展望。     

Histone Deacetylase 10 Regulates DNA Mismatch Repair and May Involve the Deacetylation of MutS Homolog 2

MutS homolog 2 (MSH2) is an essential DNA mismatch repair (MMR) protein. It interacts with MSH6 or MSH3 to form the MutSα or MutSβ complex, respectively, which recognize base-base mispairs and insertions/deletions and initiate the repair process. Mutation or dysregulation of MSH2 causes genomic instability that can lead to cancer. MSH2 is acetylated at its C terminus, and histone deacetylase (HDAC6) deacetylates MSH2. However, whether other regions of MSH2 can be acetylated and whether other histone deacetylases (HDACs) and histone acetyltransferases (HATs) are involved in MSH2 deacetylation/acetylation is unknown. Here, we report that MSH2 can be acetylated at Lys-73 near the N terminus. Lys-73 is highly conserved across many species. Although several Class I and II HDACs interact with MSH2, HDAC10 is the major enzyme that deacetylates MSH2 at Lys-73. Histone acetyltransferase HBO1 might acetylate this residue. HDAC10 overexpression in HeLa cells stimulates cellular DNA MMR activity, whereas HDAC10 knockdown decreases DNA MMR activity. Thus, our study identifies an HDAC10-mediated regulatory mechanism controlling the DNA mismatch repair function of MSH2.     

高等植物开花时程的基因调控（Ⅰ）

高等植物从营养生长向生殖生长及发育转变的时程具有重要意义,但是了解得很少。近6年来利用分子遗传学方法详细地分析了拟南芥中的这一转变的时程变化,为高等植物开花时程的基因调控提供了一个很好的模式。有关早期或晚期开花表现型的大量突变体及遗传变异得到了阐述。这里谈到的表现型对影响开花转变的环境及内部因子的控制有重大作用。通过分子生物学、遗传学和生理学分析已经鉴定了参与此过程的不同组分,如光识别和昼夜节律（circadian rhythm）因子。另外,通过克隆某些花诱导基因及其相应的靶基因已经对参与开花信号转导途径（signal transduction pathway）的相关因子进行了系统的鉴定,这些开创性工作大大促进了高等植物开花时程的基因表达调控研究及其机理的阐明。本实验室在以黄瓜、新红宝西瓜、西葫芦为材料所获得的部分结果基础上,主要以近六年来在拟南芥方面获得的进展为依据,对高等植物开花时程的基因调控作一系统的总结,并对其开花时程基因调控的机理提出可能的作用理论模型。     

Intermittent Illumination and the Photoperiodic Control of Flowering in Carnation

Plants of glasshouse carnation, a facultative long-day plant,were grown in photoperiodic cycles comprising 8 h natural daylightfollowed by 16-h ‘nights’. Throughout the nightseither continuous or intermittent lighting was given from tungsten-filamentlamps. Intermittent lighting comprised 15-min cycles of 5 or 6 minof light followed by 10 or 9 min of dark. This was as effectiveas continuous lighting in promoting flower initiation providinglight intensities were adjusted to give the same total lightenergy per night. If the same light intensity was used for bothcontinuous and intermittent lighting their relative effectivenessdepended on a number of factors. Superiority of the continuous-lightingtreatment in promoting flower initiation was apparent when theintensity of light was very low, when the treatments were givenfor relatively few nights or where shoots were illuminated atan early stage of growth. The use of intermittent lighting did not offer any obvious practicaladvantages as a means of controlling flowering in carnation.     

Serine Involvement in the Flowering of Lemna during Photoperiodic Induction

The levels of the endogenous free amino acid serine in Lemnaperpusilla are found to fluctuate during the course of shortdays. Serine levels do not change in plants receiving long daysor continuous light. The levels of serine decrease graduallyin the dark reaction of short days reaching their lowest aboutthe middle of the dark period, indicating a utilization of serineduring the dark reaction. In the second half of the dark periodthe serine level rises. The decline and rise of serine duringthe dark period is observed in successive short-day cycles.During the light period the serine level increases, reachinga maximum after 6 h from the beginning of the light exposure.When the light period is eliminated and a continuous dark periodis given the serine level remains unchanged. It is suggestedthat serine is involved in the floral initiation as a precursorto a flowering substance.