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。     

拟南芥开花时间调控的研究进展

调控开花时间是大多数植物由营养生长向生殖生长转化的一个重要生长发育过程.影响拟南芥开花时间的因素有很多,其中光照和温度是两个主要的外部因素,而赤霉素(GA)和一些自主性因子是主要的内部因素.目前,一般按照对以上因素的反应将晚花突变体归于四条开花调控途径:光周期途径、春化途径、自主途径和GA途径.在不断变化的外部环境条件和内部生理条件下,这些途径通过一些主要的整合基因如SOC1、FT、LFY等实现了对拟南芥开花时间的精确调控.     

控制拟南芥和水稻开花时间光周期途径的分子机制

就拟南芥和水稻开花时间控制光周期途径的分子机制的研究进展作简要介绍。     

拟南芥开花时间调控的整合途径

拟南芥开花时间受光周期途径、春化途径、自主途径和赤霉素途径4条途径调控。开花途径整合因子LEAFY、SDC1和FT等可整合来自不同开花途径的信号,并将信号传递给花分生组织基因,从而实现对拟南芥开花时间的精确调控。文章就整合途径基因调控网络的最新研究进展作简要介绍。     

植物开花时间的遗传调控通路研究进展

开花时间对植物的繁殖成功至关重要。广泛分布的物种经常发生开花时间的分化, 从而能够更好地适应不同的环境条件。为了探索植物开花行为发生适应性分化的分子机制, 首先要明确调控开花行为的遗传通路。本文梳理了植物各类群调控开花时间的遗传通路, 以期为开花时间适应性分化的分子机制研究提供依据。 植物从营养生长向繁殖转变时, 其开花行为主要受到光照、温度、水分等外界环境因子和赤霉素等内在因素的影响。通过对模式植物拟南芥(Arabidopsis thaliana)和其他类群的研究, 总结出了调控植物开花时间的6条通路, 包括日照长度和光质影响开花的光依赖通路, 长时间冷暴露后促进植物开花的春化通路, 高温或低温环境影响开花的温度通路, 以及赤霉素通路、年龄通路和自主通路3条内部调节过程。植物开花时间调控的6条上游通路信号传递到下游的开花整合基因FT(FLOWERING LOCUS T)和SOC1(SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1), 整合基因将这些复杂的调节因子整合后进一步传递到下游花分生组织, 从而启动开花。此外, 非编码RNA、转座子对开花时间的调控也具有重要作用。部分遗传通路被证实在植物适应环境的过程中起到了重要作用。目前对植物开花调控的研究已经有一百多年历史, 理论相对成熟。然而, 仍然存在许多具有争议和未解决的问题, 如开花基因的表达方式、开花行为的特殊调控机制、开花时间变异的适应性意义等等, 需要更进一步的研究。     

植物开花时间调控的信号途径

开花是植物从营养生长到生殖生长的一个重要转折点。花启动的时机对生殖生长的成功至关重要。开花时间受内在因子和环境因子的共同调节。通过对拟南芥的分子遗传学研究,确定至少存在4条调控开花时间的信号途径,即光周期途径、春化途径、自主途径和赤霉素途径。本文以拟南芥 (Arabidopsis thaliana) 为主要研究对象简要综述了近年来在开花时间调控领域的研究进展。     

高等植物开花时程的调控与光受体Ⅱ.光受体调控开花时程的分子机制与昼夜节律时间钟

系统评述了高等植物开花时程的调控与植物光受体的联系.重点说明了控制开花时程的遗传途径以及光周期途径的有关基因的研究进展.而且对植物光受体调控高等植物开花里程的分子机制作了深入的探讨.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.控制高等植物开花时程及其性别表达的关键就在此过程中.植物光受体参与了高等植物开花时程的调控并起到了重要作用.植物光受体主要包括植物光敏素受体(光敏素A、B、D、E受体)和隐色素受体.近5年左右的时间通过对拟南芥及其一系列突变体的研究展示了这一热门领域的广阔的理论与应用前景.     

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。     

拟南芥开花过程的表观遗传调节

开花是高等植物由营养生长到生殖生长的重要转变.拟南芥的开花时间受许多基因的调控,其中一些基因的表现遗传调节对开花时间的控制发挥着重要的作用.本文就这些基因以表观遗传方式调节拟南芥开花过程的最新研究进程作简要介绍.     

Genetic basis of adaptation: flowering time in Arabidopsis thaliana

 We have mapped QTLs (quantitative trait loci) for an adaptive trait, flowering time, in a selfing annual, Arabidopsis thaliana. To obtain a mapping population we made a cross between an early-summer, annual strain, Li-5, and an individual from a late over-wintering natural population, Naantali. From the backcross to Li-5 298 progeny were grown, of which 93 of the most extreme individuals were genotyped. The data were analysed with both interval mapping and composite interval mapping methods to reveal one major and six minor QTLs, with at least one QTL on each of the five chromosomes. The QTL on chromosome 4 was a major one with an effect of 17.3 days on flowering time and explaining 53.4% of the total variance. The others had effects of at most 6.5 days, and they accounted for only small portions of the variance. Epistasis was indicated between one pair of the QTLs. The result of finding one major QTL and little epistasis agrees with previous studies on flowering time in Arabidopsis thaliana and other species. That several QTLs were found was expected considering the large number of possible candidate loci. In the light of the suggested genetic models of gene action at the candidate loci, epistasis was to be expected. The data showed that major QTLs for adaptive traits can be detected in non-domesticated species. Received: 15 January 1997/Accepted: 21 February 1997     

Pleiotropic effects of flowering time genes in the annual crucifer Arabidopsis thaliana (Brassicaceae)

Variation in flowering time of Arabidopsis thaliana was studied in an experiment with mutant lines. The pleiotropic effects of flowering time genes on morphology and reproductive yield were assessed under three levels of nutrient supply. At all nutrient levels flowering time and number of rosette leaves at flowering varied among mutant lines. The relationship between these two traits depended strongly on nutrient supply. A lower nutrient supply first led to an extension of the vegetative phase, while the mean number of leaves at flowering was hardly affected. A further reduction resulted in no further extension of the vegetative phase and, on average, plants started flowering with a lower leaf number. At low nutrients, early flowering affected the timing of production of siliques rather than the total output, whereas late flowering was favorable at high nutrients. This may explain the fact that many plant species flower at a relatively small size under poor conditions. Flowering time genes had pleiotropic effects on the leaf length, number of rosette and cauline leaves, and number of axillary flowering shoots of the main inflorescence. Silique production was positively correlated with the number of axillary shoots of the main inflorescence; the number of axillary primordia appeared to have a large impact on reproductive yield.     

拟南芥反应调节因子研究进展

反应调节因子是His_Asp磷酸转移信号传导途径的重要组分。它通过在保守的Asp残基上接受由感受器转移而来的磷酸基团对下游基因进行调控 ,以对环境刺激作出反应。在高等植物拟南芥中已经发现 1 4种反应调节因子 ,它们可分为A ,B两种亚型。在结构上 ,B亚型反应调节因子的B盒序列和较长的C末端延伸使其具有转录因子的作用 ;在表达特性上 ,A亚型反应调节因子的转录受细胞分裂素和硝酸盐诱导 ;在生化特性上 ,A亚型反应调节因子具有磷酸化酶活性 ,而B亚型反应调节因子可能是AHPs的磷酸提供者     

Analysis of leaf proteins in late flowering mutants of Arabidopsis thaliana

Late flowering monogenic mutants of Arabidopsis thaliana (L.) Heynh. at the loci co, gi, fca, fve, fwa, fha, fpa, fy and their corresponding wild type, Landsberg erecta , were analysed by two-dimensional gel electrophoresis. All plants were grown under continuous light and proteins were extracted from leaves of the same age (20-day-old). The polypeptide patterns of the mutants at the loci co, gi, fca, fve, fwa, fha, fpa , and Landsberg erecta were identical. The mutant at the fy locus showed a qualitative difference with Landsberg erecta . Crosses were made between this line and the wild type Landsberg erecta . F2 plants, resulting from autopollination of the hybrid, were analysed and showed no cosegregation between the observed protein and the flowering phenotype, indicating that these two lines differ by more than a single mutation.     

Variation at two flowering time genes within and among populations of Arabidopsis thaliana: comparison with markers and traits

Flowering Locus C (FLC) and Frigida are two interacting genes controlling flowering time variation in Arabidopsis thaliana. Variation at these genes was surveyed in 12 A. thaliana populations sampled in France. These populations were also screened for variation at molecular markers [12 microsatellites and 19 cleaved amplified polymorphic sequence (CAPS) markers] and at seven quantitative traits measured with and without vernalization. Seven populations were highly polymorphic at markers (H(S) = 0.57 at microsatellites, 0.24 at CAPS) and showed heritable variation for bolting time and some other traits. Five populations were genetically fixed or nearly fixed. Q(ST) for bolting time without vernalization was significantly higher than F(ST), suggesting local divergent selection. One of the two haplotype groups at FLC (FLC(A)) was very predominant (frequency of 99%). The first exon of Frigida showed elevated nonsynonymous variation, and nine loss-of-function mutations were found throughout the gene. The association between loss-of-function and earlier bolting was confirmed. Overall, 18 Frigida haplotypes were detected. The pattern of variation at Frigida was largely similar to that found at markers and traits, with the same populations being fixed or highly diverse. Metapopulation dynamics is thus probably the main factor shaping genetic variation in A. thaliana. However, F(ST) for functional (FRI) vs. nonfunctional (FRI(Delta)) haplotypes was significantly higher than F(ST) at markers. This suggested that loss-of-function at Frigida is under local selection for flowering time.     

Effects of gene expression on molecular evolution in Arabidopsis thaliana and Arabidopsis lyrata

We analyzed the complete genome sequence of Arabidopsis thaliana and sequence data from 83 genes in the outcrossing A. lyrata, to better understand the role of gene expression on the strength of natural selection on synonymous and replacement sites in Arabidopsis. From data on tRNA gene abundance, we find a good concordance between codon preferences and the relative abundance of isoaccepting tRNAs in the complete A. thaliana genome, consistent with models of translational selection. Both EST-based and new quantitative measures of gene expression (MPSS) suggest that codon preferences derived from information on tRNA abundance are more strongly associated with gene expression than those obtained from multivariate analysis, which provides further support for the hypothesis that codon bias in Arabidopsis is under selection mediated by tRNA abundance. Consistent with previous results, analysis of protein evolution reveals a significant correlation between gene expression level and amino acid substitution rate. Analysis by MPSS estimates of gene expression suggests that this effect is primarily the result of a correlation between the number of tissues in which a gene is expressed and the rate of amino acid substitution, which indicates that the degree of tissue specialization may be an important determinant of the rate of protein evolution in Arabidopsis.     

Standing genetic variation in FRIGIDA mediates experimental evolution of flowering time in Arabidopsis

The role of standing genetic variation in adaptive evolution remains unclear. Although there has been much progress in identifying candidate genes that underlie adaptive traits, we still lack direct evidence that natural allelic variation in these genes can actually mediate adaptive evolution. In this study, we investigate the role of natural allelic variation in two candidate flowering time genes, in response to selection for early flowering in Arabidopsis thaliana : FRIGIDA ( FRI ) and FLOWERING LOCUS C ( FLC ). We performed artificial selection for early flowering under 'spring-' and 'winter-annual' growth conditions using an outbred population of A. thaliana produced by intermating 19 natural accessions. FRI and FLC are involved in A. thaliana 's response to winter conditions, and nonfunctional and weak alleles at these loci are know to reduce flowering time, particularly under spring-annual conditions. Our results provide direct evidence that natural allelic variation in FRI can provide rapid and predictable adaptive evolution in flowering time under spring-annual conditions. We observed a strong response to selection, in terms of reducing flowering time, in both growth conditions (~2 standard deviation reduction). Concomitantly, the frequency of functional FRI alleles under spring-annual conditions was reduced by 68%, in agreement with predicted changes. No significant changes in allele frequencies were observed in FRI in the winter-annual growth condition or in FLC for either growth conditions. These results indicate that changes in flowering time are mediated by different genetic factors under spring- and winter-annual growth conditions, and that other loci must also be contributing to the response to selection.