MYB transcription factors in Arabidopsis

We attempted to overexpress chalcone synthase (CHS) in pigmented petunia petals by introducing a chimeric petunia CHS gene. Unexpectedly, the introduced gene created a block in anthocyanin biosynthesis. Forty-two percent of plants with the introduced CHS gene produced totally white flowers and/or patterned flowers with white or pale nonclonal sectors on a wild-type pigmented background; none of hundreds of transgenic control plants exhibited such phenotypes. Progeny testing of one plant demonstrated that the novel color phenotype co-segregated with the introduced CHS gene; progeny without this gene were phenotypically wild type. The somatic and germinal stability of the novel color patterns was variable. RNase protection analysis of petal RNAs isolated from white flowers showed that, although the developmental timing of mRNA expression of the endogenous CHS gene was not altered, the level of the mRNA produced by this gene was reduced 50-fold from wild-type levels. Somatic reversion of plants with white flowers to phenotypically parental violet flowers was associated with a coordinate rise in the steady-state levels of the mRNAs produced by both the endogenous and the introduced CHS genes. Thus, in the altered white flowers, the expression of both genes was coordinately suppressed, indicating that expression of the introduced CHS gene was not alone sufficient for suppression of endogenous CHS transcript levels. The mechanism responsible for the reversible co-suppression of homologous genes in trans is unclear, but the erratic and reversible nature of this phenomenon suggests the possible involvement of methylation.

Introduction of a Chimeric Chalcone Synthase Gene into Petunia Results in Reversible Co-Suppression of Homologous Genes in trans.

The role of flavonoids as the major red, blue, and purple pigments in plants has gained these secondary products a great deal of attention over the years. From the first description of acid and base effects on plant pigments by Robert Boyle in 1664 to the characterization of structural and

Flavonoid Biosynthesis. A Colorful Model for Genetics, Biochemistry, Cell Biology, and Biotechnology

Our knowledge of the structure and composition of genomes is rapidly progressing in pace with their sequencing. The emerging data show that a significant portion of eukaryotic genomes is composed of transposable elements (TEs). Given the abundance and diversity of TEs and the speed at which large quantities of sequence data are emerging, identification and annotation of TEs presents a significant challenge. Here we propose the first unified hierarchical classification system, designed on the basis of the transposition mechanism, sequence similarities and structural relationships, that can be easily applied by non-experts. The system and nomenclature is kept up to date at the WikiPoson web site.

A unified classification system for eukaryotic transposable elements

MUCKE aims to mine a large volume of images, to structure them conceptually and to use this conceptual structuring in order to improve large-scale image retrieval. The last decade witnessed important progress concerning low-level image representations. However, there are a number problems which need to be solved in order to unleash the full potential of image mining in applications. The central problem with low-level representations is the mismatch between them and the human interpretation of image content. This problem can be instantiated, for instance, by the incapability of existing descriptors to capture spatial relationships between the concepts represented or by their incapability to convey an explanation of why two images are similar in a content-based image retrieval framework. We start by assessing existing local descriptors for image classification and by proposing to use co-occurrence matrices to better capture spatial relationships in images. The main focus in MUCKE is on cleaning large scale Web image corpora and on proposing image representations which are closer to the human interpretation of images. Consequently, we introduce methods which tackle these two problems and compare results to state of the art methods. Note: some aspects of this deliverable are withheld at this time as they are pending review. Please contact the authors for a preview.

http://ieeexplore.ieee.org/iel2/4524/12820/00592460.pdf

Image Processing

The structure of the wild-type c1 locus of Zea mays was determined by sequence analysis of one genomic and two cDNA clones. The coding region is composed of three exons (150 bp, 129 bp and one, at least 720 bp) and two small introns (88 bp and 145 bp). Transcription of the mRNAs corresponding to the two cDNA clones cLC6 (1.1 kb) and cLC28 (2.1 kb) starts from the same promoter. Both cDNAs are identical except that cLC28 extends further at its 3' end. A putative protein, 273 amino acids in length was deduced from the sequence of both transcripts. It contains two domains, one basic and the other acidic and might function as a transcriptional activator. The basic domain of this c1-encoded protein shows 40% sequence homology to the protein products of animal myb proto-oncogenes.

The regulatory c1 locus of Zea mays encodes a protein with homology to myb proto-oncogene products and with structural similarities to transcriptional activators.

Throughout development the Arabidopsis shoot apical meristem successively undergoes several major phase transitions such as the juvenile-to-adult and floral transitions until, finally, it will produce flowers instead of leaves and shoots. Members of the Arabidopsis SBP-box gene family of transcription factors have been implicated in promoting the floral transition in dependence of miR156 and, accordingly, transgenics constitutively over-expressing this microRNA are delayed in flowering. To elaborate their roles in Arabidopsis shoot development, we analysed two of the 11 miR156 regulated Arabidopsis SBP-box genes, i.e. the likely paralogous genes SPL9 and SPL15. Single and double mutant phenotype analysis showed these genes to act redundantly in controlling the juvenile-to-adult phase transition. In addition, their loss-of-function results in a shortened plastochron during vegetative growth, altered inflorescence architecture and enhanced branching. In these aspects, the double mutant partly phenocopies constitutive MIR156b over-expressing transgenic plants and thus a major contribution to the phenotype of these transgenics as a result of the repression of SPL9 and SPL15 is strongly suggested.

/pdf/the-microrna-regulated-sbp-box-genes-spl9-and-spl15-control-3fpyi26cq9.pdf

The microRNA regulated SBP-box genes SPL9 and SPL15 control shoot maturation in Arabidopsis

Publisher Summary In plants, variegation is most easily recognized as irregularities in pigment patterns on leaves, flowers, and seeds, although other characteristics such as leaf form, flower form, or starch content (in maize kernels) may also be subject to variegation This chapter focuses on variegation in plants due to genetic alterations implemented by transposable elements The distinguishing feature of this kind of variegation, as opposed to other examples discussed, is that the two or more different kinds of tissue in the variegated plant differ genotypically, that is, with respect to the DNA of their nuclear genomes In the simplest case, one kind of tissue contains a transposable element at a given locus and the other does not The term “transposable element” rather than “controlling element” is used to avoid confusion with the terminology of other fields of genetic research First, data from molecular research that have provided new criteria beyond those obtained by classical genetic methods are discussed Thus, DNA sequence analyses have shown that transposable elements may share certain structural features that might be useful for classification Furthermore, transposition can now be demonstrated by DNA hybridization techniques that were unknown 20 years ago In general, a transposable element is characterized by its ability to integrate into the DNA at some position in the genome and thereby alter the expression of the gene(s) in and around itself

Plant Transposable Elements

Petunia hybrida is one of the classical subjects of investigation in plants in which the pathway of anthocyanin biosynthesis has been analysed genetically and biochemically. In petunia cyanidin- and delphinidin-derivatives, but no pelargonidin-derivatives are produced as pigments. This is due to the substrate specificity of the dihydroflavonol 4-reductase of petunia, which cannot reduce dihydrokaempferol. The petunia mutant RL01, which accumulates dihydrokaempferol, shows no flower pigmentation. RL01 served as a recipient for the transfer of the A1 gene of Zea mays encoding dihydroquercetin 4-reductase, which can reduce dihydrokaempferol and thereby provided the intermediate for pelargonidin biosynthesis. Transformation of RL01 with a vector p35A1, containing the A1-complementary DNA behind the 35S promotor leads to red flowers of the pelargonidin-type. Thus a new flower pigmentation pathway has been established in these plants.

A new petunia flower colour generated by transformation of a mutant with a maize gene

Visual screening of a T-DNA mutagenised population of Arabidopsis thaliana for an absence of silique elongation lead to the isolation of the aborted microspores (ams) mutant that shows a sporophytic recessive male sterile phenotype. Homozygous mutant plants are completely devoid of mature pollen. Pollen degeneration occurs shortly after release of the microspores from the tetrad, prior to pollen mitosis I. Premature tapetum and microspore degeneration are the primary defects caused by this lesion, while a secondary effect is visualised in the stamen filaments, which are reduced in length and lie beneath the receptive stigma at flower opening. The disrupted gene was isolated and revealed a T-DNA element to be inserted into the eighth exon of a basic helix-loop-helix (bHLH) gene located on chromosome II. This protein sequence contains a basic DNA binding domain and two alpha helices separated by a loop, typical of a transcription factor belonging to the MYC sub family of bHLH genes. Therefore, AMS plays a crucial role in tapetal cell development and the post-meiotic transcriptional regulation of microspore development within the developing anther.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-313X.2003.01644.x

Heinz Saedler

Papers

The regulatory c1 locus of Zea mays encodes a protein with homology to myb proto-oncogene products and with structural similarities to transcriptional activators.

The microRNA regulated SBP-box genes SPL9 and SPL15 control shoot maturation in Arabidopsis

Plant Transposable Elements

A new petunia flower colour generated by transformation of a mutant with a maize gene

The Arabidopsis ABORTED MICROSPORES (AMS) gene encodes a MYC class transcription factor