Cell Specific,Cross-Species Expression of Myrosinases in Brassica Napus,Arabidopsis Thaliana and Nicotiana Tabacum

A prototypical characteristic of the Brassicaceae is the presence of the myrosinase-glucosinolate system. Myrosinase, the only known S-glycosidase in plants, degrades glucosinolates, thereby initiating the formation of isothiocyanates, nitriles and other reactive products with biological activities. We have used myrosinase gene promoters from Brassica napus and Arabidopsis thaliana fused to the beta -glucuronidase (GUS) reporter gene and introduced into Arabidopsis thaliana, Brassica napus and/or Nicotiana tabacum plants to compare and determine the cell types expressing the myrosinase genes and the GUS expression regulated by these promoters. The A. thaliana TGG1 promoter directs expression to guard cells and phloem myrosin cell idioblasts of transgenic A. thaliana plants. Expression from the same promoter construct in transgenic tobacco plants lacking the myrosinase enzyme system also directs expression to guard cells. The B. napus Myr1.Bn1 promoter directs a cell specific expression to idioblast myrosin cells of immature and mature seeds and myrosin cells of phloem of B. napus. In A. thaliana the B. napus promoter directs expression to guard cells similar to the expression pattern of TGG1. The Myr1.Bn1 signal peptide targets the gene product to the reticular myrosin grains of myrosin cells. Our results indicate that myrosinase gene promoters from Brassicaceae direct cell, organ and developmental specific expression in B. napus, A. thaliana and N. tabacum.     

通过白菜型油菜和埃塞俄比亚芥的Ar和Cc基因组导入创造甘蓝型油菜新材料

油菜是目前我国主要种植的油料作物之一,但现有的种质资源限制了产量的进一步提高。本研究采取了一种新的育种方式来增加甘蓝型油菜的种质资源,即通过远缘杂交结合分子标记辅助选择的方式将白菜型油菜的Ar基因组和埃塞俄比亚芥的Cc对现有的甘蓝型油菜品种的基因组(AnAnCnCn)进行部分替换。通过对五倍体杂交后代(ArAnBcCcCn)进行染色体选择,找到了染色体数目为38的材料。为了和现有的甘蓝型油菜进行区分,得到的新材料被认定为甘蓝型油菜新材料。实验结果表明,得到的部分甘蓝型油菜新材料具有基本正常的减数分裂过程、正常的花粉萌发以及胚囊发育过程,这说明甘蓝型油菜新材料达到了遗传平衡。分子标记分析表明:甘蓝型油菜新材料的约50%的基因组被白菜型油菜的Ar基因组和埃塞俄比亚芥的Cc替换,并且这些甘蓝型油菜新材料之间具有丰富的遗传多样性。因此,白菜型油菜的Ar基因组和埃塞俄比亚芥的Cc基因组导入对于丰富现有的甘蓝型油菜种质资源具有明显的效果。     

与拟南芥春化作用相关的基因及其春化记忆模型

植物能感应春化并记住这一效应,且通过一系列的信号传导,最终调控开花。文章就拟南芥的春化相关的基因,春化记忆分子模型、春化记忆与开花调控途径以及与此不同的另一种春化记忆模型和小麦春化记忆分子机制的研究进展作了介绍。     

Interactions among Genes Regulating Ovule Development in Arabidopsis Thaliana

The INNER NO OUTER (INO) and AINTEGUMENTA (ANT) genes are essential for ovule integument development in Arabidopsis thaliana. Ovules of ino mutants initiate two integument primordia, but the outer integument primordium forms on the opposite side of the ovule from the normal location and undergoes no further development. The inner integument appears to develop normally, resulting in erect, unitegmic ovules that resemble those of gymnosperms. ino plants are partially fertile and produce seeds with altered surface topography, demonstrating a lineage dependence in development of the testa. ant mutations affect initiation of both integuments. The strongest of five new ant alleles we have isolated produces ovules that lack integuments and fail to complete megasporogenesis. ant mutations also affect flower development, resulting in narrow petals and the absence of one or both lateral stamens. Characterization of double mutants between ant, ino and other mutations affecting ovule development has enabled the construction of a model for genetic control of ovule development. This model proposes parallel independent regulatory pathways for a number of aspects of this process, a dependence on the presence of an inner integument for development of the embryo sac, and the existence of additional genes regulating ovule development.     

GAMYB-like Genes, Flowering, and Gibberellin Signaling in Arabidopsis

We have identified three Arabidopsis genes with GAMYB-like activity, AtMYB33, AtMYB65, and AtMYB101, which can substitute for barley (Hordeum vulgare) GAMYB in transactivating the barley alpha-amylase promoter. We have investigated the relationships between gibberellins (GAs), these GAMYB-like genes, and petiole elongation and flowering of Arabidopsis. Within 1 to 2 d of transferring plants from short- to long-day photoperiods, growth rate and erectness of petioles increased, and there were morphological changes at the shoot apex associated with the transition to flowering. These responses were accompanied by accumulation of GAs in the petioles (GA(1) by 11-fold and GA(4) by 3-fold), and an increase in expression of AtMYB33 at the shoot apex. Inhibition of GA biosynthesis using paclobutrazol blocked the petiole elongation induced by long days. Causality was suggested by the finding that, with GA treatment, plants flowered in short days, AtMYB33 expression increased at the shoot apex, and the petioles elongated and grew erect. That AtMYB33 may mediate a GA signaling role in flowering was supported by its ability to bind to a specific 8-bp sequence in the promoter of the floral meristem-identity gene, LEAFY, this same sequence being important in the GA response of the LEAFY promoter. One or more of these AtMYB genes may also play a role in the root tip during germination and, later, in stem tissue. These findings extend our earlier studies of GA signaling in the Gramineae to include a dicot species, Arabidopsis, and indicate that GAMYB-like genes may mediate GA signaling in growth and flowering responses.     

Analysis of Flowering Time Control in Arabidopsis by Comparison of Double and Triple Mutants

Three genetic pathways promote flowering of Arabidopsis under long photoperiods. These pathways are represented by the genes CO, FCA, and GA1, which act in the long-day, autonomous, and gibberellin pathways, respectively. To test whether these are the only pathways that promote flowering under long photoperiods, the co-2 fca-1 ga1-3 triple mutant was constructed. These plants never flowered under long- or short-day conditions, indicating that the three pathways impaired by these mutations are absolutely required for flowering under these conditions. The triple mutant background represents a "vegetative ground state" enabling the roles of single pathways to be described in the corresponding double mutants. The phenotypes of plants carrying all eight combinations of wild-type and mutant alleles at the three loci were compared under long- and short-day conditions. This analysis demonstrated that under long photoperiods the long-day pathway promoted flowering most effectively, whereas under short photoperiods the gibberellin pathway had the strongest effect. The autonomous pathway had a weak effect when acting alone under either photoperiod but appeared to play an important role in facilitating the promotion of flowering by the other two pathways. The vegetative phenotype of the triple mutant could be overcome by vernalization, suggesting that a fourth pathway promoted flowering under these conditions. These observations are discussed in light of current models describing the regulation of flowering time in Arabidopsis.     

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。     

Structure and Evolution of Genes Encoding Polyubiquitin and Ubiquitin-like Proteins in Arabidopsis Thaliana Ecotype Columbia

The Arabidopsis thaliana ecotype Columbia ubiquitin gene family consists of 14 members that can be divided into three types of ubiquitin genes; polyubiquitin genes, ubiquitin-like genes and ubiquitin extension genes. The isolation and characterization of eight ubiquitin sequences, consisting of four polyubiquitin genes and four ubiquitin-like genes, are described here, and their relationships to each other and to previously identified Arabidopsis ubiquitin genes were analyzed. The polyubiquitin genes, UBQ3, UBQ10, UBQ11 and UBQ14, contain tandem repeats of the 228-bp ubiquitin coding region. Together with a previously described polyubiquitin gene, UBQ4, they differ in synonymous substitutions, number of ubiquitin coding regions, number and nature of nonubiquitin C-terminal amino acid(s) and chromosomal location, dividing into two subtypes; the UBQ3/UBQ4 and UBQ10/UBQ11/UBQ14 subtypes. Ubiquitin-like genes, UBQ7, UBQ8, UBQ9 and UBQ12, also contain tandem repeats of the ubiquitin coding region, but at least one repeat per gene encodes a protein with amino acid substitutions. Nucleotide comparisons, K(s) value determinations and neighbor-joining analyses were employed to determine intra- and intergenic relationships. In general, the rate of synonymous substitution is too high to discern related repeats. Specific exceptions provide insight into gene relationships. The observed nucleotide relationships are consistent with previously described models involving gene duplications followed by both unequal crossing-over and gene conversion events.     

Cytosolic, Mitochondrial Thioredoxins and Thioredoxin Reductases in Arabidopsis Thaliana

Thioredoxins, by reducing disulfide bridges are one of the main participants that regulate cellular redox balance. In plants, the thioredoxin system is particularly complex. The most well-known thioredoxins are the chloroplastic ones, that participate in the regulation of enzymatic activities during the transition between light and dark phases. The mitochondrial system composed of NADPH-dependent thioredoxin reductase and type o thioredoxin has only recently been described. The type h thioredoxin group is better known. Yeast complementation experiments demonstrated that Arabidopsis thaliana thioredoxins h have divergent functions, at least in Saccharomyces cerevisiae. They have diverse affinities for different target proteins, most probably because of structural differences. However, plant thioredoxin h functions still have to be defined.     

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。     

Uv- and Gamma-Radiation Sensitive Mutants of Arabidopsis Thaliana

Arabidopsis seedlings repair UV-induced DNA damage via light-dependent and -independent pathways. The mechanism of the ``dark repair' pathway is still unknown. To determine the number of genes required for dark repair and to investigate the substrate-specificity of this process we isolated mutants with enhanced sensitivity to UV radiation in the absence of photoreactivating light. Seven independently derived UV sensitive mutants were isolated from an EMS-mutagenized population. These fell into six complementation groups, two of which (UVR1 and UVH1) have previously been defined. Four of these mutants are defective in the dark repair of UV-induced pyrimidine [6-4] pyrimidinone dimers. These four mutant lines are sensitive to the growth-inhibitory effects of gamma radiation, suggesting that this repair pathway is also involved in the repair of some type of gamma-induced DNA damage product. The requirement for the coordinate action of several different gene products for effective repair of pyrimidine dimers, as well as the nonspecific nature of the repair activity, is consistent with nucleotide excision repair mechanisms previously described in Saccharomyces cerevisiae and nonplant higher eukaryotes and inconsistent with substrate-specific base excision repair mechanisms found in some bacteria, bacteriophage, and fungi.     

A Brassica rapa Linkage Map of EST-based SNP Markers for Identification of Candidate Genes Controlling Flowering Time and Leaf Morphological Traits

For identification of genes responsible for varietal differences in flowering time and leaf morphological traits, we constructed a linkage map of Brassica rapa DNA markers including 170 EST-based markers, 12 SSR markers, and 59 BAC sequence-based markers, of which 151 are single nucleotide polymorphism (SNP) markers. By BLASTN, 223 markers were shown to have homologous regions in Arabidopsis thaliana, and these homologous loci covered nearly the whole genome of A. thaliana. Synteny analysis between B. rapa and A. thaliana revealed 33 large syntenic regions. Three quantitative trait loci (QTLs) for flowering time were detected. BrFLC1 and BrFLC2 were linked to the QTLs for bolting time, budding time, and flowering time. Three SNPs in the promoter, which may be the cause of low expression of BrFLC2 in the early-flowering parental line, were identified. For leaf lobe depth and leaf hairiness, one major QTL corresponding to a syntenic region containing GIBBERELLIN 20 OXIDASE 3 and one major QTL containing BrGL1, respectively, were detected. Analysis of nucleotide sequences and expression of these genes suggested possible involvement of these genes in leaf morphological traits.     

油菜硫甙性状QTL 区间的加密和整合

目的:加密油菜控制硫甙性状QTL区间,并进行QTL整合预测候选基因。方法:利用生物信息学方法根据已知测序的白菜BAC序列信息设计引物,在油菜TN DH群体中进行多态性扩增和定位,并根据加密后构建的遗传连锁图重新检测QTL,进行QTL整合。结果:将根据白菜BAC设计的3对多态性标记成功定位到油菜控制硫甙性状QTL区间,进行QTL整合后将QTL置信区间进一步缩小,并判定了初步的候选基因。结论:充分利用白菜已测序的BAC或者基因组信息,将能加快油菜基础研究的步伐。