Programmed cell death (PCD) has a key role in defence and development of all multicellular organisms. In plants, there is a large gap in our knowledge of the molecular machinery involved at the various stages of PCD, especially the early steps. Here, we identify kiss of death (KOD) encoding a 25-amino-acid peptide that activates a PCD pathway in Arabidopsis thaliana. Two mutant alleles of KOD exhibited a reduced PCD of the suspensor, a single file of cells that support embryo development, and a reduced PCD of root hairs after a 55°C heat shock. KOD expression was found to be inducible by biotic and abiotic stresses. Furthermore, KOD expression was sufficient to cause death in leaves or seedlings and to activate caspase-like activities. In addition, KOD-induced PCD required light in leaves and was repressed by the PCD-suppressor genes AtBax inhibitor 1 and p35. KOD expression resulted in depolarization of the mitochondrial membrane, placing KOD above mitochondria dysfunction, an early step in plant PCD. A KOD∷GFP fusion, however, localized in the cytosol of cells and not mitochondria.

In this review we describe three recent genetic studies that implicate thioredoxins (TRX) and glutaredoxins (GRX) in higher plant development. Firstly, ROXY genes, members of the plant specific CC-type GRX, are implicated in petal and anther development by controlling the nuclear activity of TGA transcription factors. Secondly, the cytosolic NADPH TRX reductase (NTR) and glutathione (GSH) pathways of TRX and GRX reduction are redundant and control apical meristem development. Finally, chloroplastic TRX m3 is implicated in plasmodesmata permeability and its inactivation blocks root growth and leaf development at an early stage after germination.These results demonstrate the power of genetic approaches for studying redox regulation in plants and reveal new functions that were previously unexpected despite an extensive structural, biochemical and proteomic literature. (C) 2010 Elsevier Ireland Ltd. All rights reserved.

We report on the structural characterization of a functional U3 snoRNA ribonucleoprotein complex isolated from Brassica oleracea. The BoU3 snoRNP complex (formerly NF D) binds ribosomal DNA (rDNA), specifically cleaves pre-rRNA at the primary cleavage site in vitro and probably links transcription to early pre-rRNA processing in vivo. Using a proteomic approach we have identified 62 proteins in the purified BoU3 snoRNP fraction, including small RNA associated proteins (Fibrillarin, NOP5/Nop58p, Diskerin/Cbf5p, SUS2/PRP8 and CLO/GFA1/sn114p) and 40S ribosomal associated proteins (22 RPS and four ARCA-like proteins). Another major protein group is composed of chaperones/chaperonins (HSP81/TCP-1) and at least one proteasome subunit (RPN1a). Remarkably, RNA-dependent RNA polymerase (RdRP) and Tudor staphylococcal nuclease (TSN) proteins, which have RNA- and/or DNA-associated activities, were also revealed in the complex. Furthermore, three U3 snoRNA variants were identified in the BoU3 snoRNP fraction, notably an evolutionarily conserved and variable stem loop structure located just downstream from the C-box domain of the U3 sequence structures. We conclude that the BoU3 snoRNP complex is mainly required for 40S pre-ribosome synthesis. It is also expected that U3 snoRNA variants and interacting proteins might play a major role in BoU3 snoRNP complex assembly and/or function. This study provides a basis for further investigation of these novel ribonucleoprotein factors and their role in plant ribosome biogenesis.

*The Arabidopsis genome possesses two confirmed Cytochrome P450 Reductase (CPR) genes, ATR1 and ATR2, together with a third putative homologue, ATR3, which annotation is questionable. *Phylogenetic analysis classified ATR3 as a CPR-like protein sharing homologies with the animal cytosolic dual flavin reductases, NR1 and Fre-1, distinct from the microsomal CPRs, ATR1 and ATR2. Like NR1 and Fre-1, ATR3 lacks the N-terminal endoplasmic reticulum (ER) anchor domain of CPRs and is localized in the cytoplasm. Recombinant ATR3 in plant soluble extracts was able to reduce cytochrome c but failed to reduce the human P450 CYP1A2. *Loss of ATR3 function resulted in early embryo lethality indicating that this reductase activity is essential. A yeast 2-hybrid screen identified a unique interaction of ATR3 with the homologue of the human anti-apoptotic CIAPIN1 and the yeast Dre2 protein. *This interaction suggests two possible roles for ATR3 in the control of cell death and in chromosome segregation at mitosis. Consistent with these results, the promoter of ATR3 is activated during cell cycle progression. Together these results demonstrated that ATR3 belongs to the NR1 subfamily of diflavin reductases whose characterized members are involved in essential cellular functions.

Re-activation of cell division after fertilization involves the specific regulation of a set of genes. To identify genes involved in the gametophytic to sporophytic transition, we screened Arabidopsis T-DNA insertion lines for early seed abortion at the zygote (zeus) or one-cell embryo stages (cyclops), and characterized a sporophytic zygote-lethal mutation, zeus1. ZEUS1 encodes a thymidylate kinase (AtTMPK) that synthesizes dTDP and is involved in the regulation of DNA replication. Unlike in yeast and animals, the single AtTMPK gene is capable of producing two proteins by alternative splicing; the longer isoform is targeted to the mitochondria, the shorter to the cytosol. Transcription of AtTMPK is activated during the G(1)/S-phase transition of the cell cycle, similarly to yeast and mammalian orthologues. In AtTMPK:GUS plants, the reporter gene was preferentially expressed in cells undergoing division, but was not detected during the male and female gametophytic mitoses. GUS expression was observed in mature embryo sacs prior to fertilization, and this expression may indicate the time of synchronization of the gamete cell-cycle phases. Identification of ZEU1 emphasizes the importance of control of the metabolism of DNA in the regulation of the G(1)/S-phase transition at fertilization.

Accurate DNA replication is one of the most important events in the life of a cell. To perform this task, the cell utilizes several DNA polymerase complexes. We investigated the role of DNA polymerase epsilon during gametophyte and seed development using forward and reverse genetic approaches. In Arabidopsis, the catalytic subunit of this complex is encoded by two genes, AtPOL2a and AtPOL2b, whereas the second largest regulatory subunit AtDPB2 is present as a unique complete copy. Disruption of AtPOL2a or AtDPB2 resulted in a sporophytic embryo-defective phenotype, whilst mutations in AtPOL2b produced no visible effects. Loss of AtDPB2 function resulted in a severe reduction in nuclear divisions, both in the embryo and in the endosperm. Mutations in AtPOL2a allowed several rounds of mitosis to proceed, often with aberrant planes of division. Moreover, AtDPB2 was not expressed during development of the female gametophyte, which requires three post-meiotic nuclear divisions. Since a consensus binding site for E2F transcription factors was identified in the promoter region of both genes, the promoter-reporter fusion technique was used to show that luciferase activity was increased at specific phases of the cell cycle in synchronized tobacco BY-2 cells. Our results support the idea that fertilization may utilize the mechanisms of cell cycle transcriptional regulation of genes to reactivate the divisions of the oosphere and central cell.

Conference Abstract| October 01 2000 Cucumber matrix metalloproteinase gene and the gene expression during senescence Dae-Jae Kim; Dae-Jae Kim *School of Science Education, Chunghuk National University, Cheong Ju, KOREA Search for other works by this author on: This Site PubMed Google Scholar Valerie Delorme; Valerie Delorme **Lab. de Physiologie et Biologic Moleculaire des Plantes, Universite de Perpignan, Perpignan cedex, Francce Search for other works by this author on: This Site PubMed Google Scholar Paul F. McCabe; Paul F. McCabe 1Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, England Search for other works by this author on: This Site PubMed Google Scholar Christopher J. Leaver Christopher J. Leaver 1Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, England Search for other works by this author on: This Site PubMed Google Scholar Biochem Soc Trans (2000) 28 (5): A173. https://doi.org/10.1042/bst028a173b Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter LinkedIn Cite Icon Cite Get Permissions Citation Dae-Jae Kim, Valerie Delorme, Paul F. McCabe, Christopher J. Leaver; Cucumber matrix metalloproteinase gene and the gene expression during senescence. Biochem Soc Trans 1 October 2000; 28 (5): A173. doi: https://doi.org/10.1042/bst028a173b Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsBiochemical Society Transactions Search Advanced Search This content is only available as a PDF. © 2000 Biochemical Society2000 Article PDF first page preview Close Modal You do not currently have access to this content.

Self-incompatibility in Brassica is controlled by a single, highly polymorphic locus that extends over several hundred kilobases and includes several expressed genes. Two stigma proteins, the S locus receptor kinase (SRK) and the S locus glycoprotein (SLG), are encoded by genes located at the S locus and are thought to be involved in the recognition of self-pollen by the stigma. We report here that two different SLG genes, SLGA and SLGB, are located at the S locus in the class II, pollen-recessive S15 haplotype. Both genes are interrupted by a single intron; however, SLGA encodes both soluble and membrane-anchored forms of SLG, whereas SLGB encodes only soluble SLG proteins. Thus, including SRK, the S locus in the S15 haplotype contains at least three members of the S gene family. The protein products of these three genes have been characterized, and each SLG glycoform was assigned to an SLG gene. Evidence is presented that the S2 and S5 haplotypes carry only one or the other of the SLG genes, indicating either that they are redundant or that they are not required for the self-incompatibility response.

rotransposon, in self-compatible Brassica napos initially suggested that SLA played an essential role in the SI response. In this study, we have characterized an SLA allele from a self-compatible B. oleracea var acephala line and show that it too is interrupted by a large insert. However, analysis of seven B. oleracea var bofryfis lines exhibiting both self-compatible and self-incompatible phenotypes showed that these lines carry an S allele very similar or identical to that of the B. oleracea var acephala line and that the SLA gene is interrupted by an insert in all seven lines. The insertion of the putative retrotransposon was shown to interfere with gene expression, with no SLA transcripts being detected by RNA gel blot analysis in a self-incompatible B. oleracea var bofryfis line carrying an interrupted SLA gene. These data indicate that a functional SLA gene is not required for the SI response in Brassica.

The S locus, which controls the self-incompatibility response in Brassica, has been shown to contain at least two genes. SLG encodes a secreted S locus glycoprotein whilst SRK encodes a putative S locus receptor kinase. SRK has been shown potentially to encode a functional kinase and genetic evidence indicates that this gene is essential for the self-incompatibility response. Here the characterization of the SRK and SLG genes of a Brassica line homozygous for the S3 haplotype is described. A 120 kDa glycoprotein was identified in stigmas and several lines of evidence indicated that this protein is encoded by the SRK3 gene. First, the 120 kDa glycoprotein was recognized by antibodies raised against peptides based on the SRK3 gene sequence. Secondly, this protein is polymorphic and, in an F2 population segregating for the S3 haplotype, was expressed only in plants possessing the S3 haplotype. Thirdly, the 120 kDa protein was expressed specifically in stigmas. Finally, the 120 kDa protein was only extracted from stigmas in the presence of detergent indicating that it is anchored in the membrane. SRK has been predicted to encode a transmembrane glycoprotein based on the deduced amino acid sequence. Located on the membrane, SRK is in a position to interface between an extracellular recognition event between pollen and pistil and an intracellular signal transduction pathway which initiates the self-incompatibility response.

The self-incompatibility reaction of cruciferous plants prevents self-fertilization and has been shown to be controlled by at least two genes situated at a single multiallelic locus, theS locus. One of these two genes, theS locus glycoprotein (SLG) gene, encodes an abundant glycoprotein secreted to the cell wall of stigma papillae. Identification of thoseS alleles present at theS locus is of prime interest when studying the self-incompatibility response and can be achieved by identifying the SLG of the stigma. Here, we show that using anti-SLG antibodies in an immunochemical analysis, combined with a SSCP (single-strand conformation polymorphism) approach to characterize the corresponding stigma-specific, SLG mRNA, allowed the identification of plants heterogeneous at theS locus among populations of plants that were thought to be homozygous for known SLG alleles. This analysis stresses the importance of testing the homozygosity at theS locus of lines considered inbred for a knownS allele as mix-up of seeds may occur during the breeding programme.

A new member of the S gene family, SLR3 (S-Locus Related 3), was identified in Brassica oleracea. This gene had a novel pattern of expression compared with previously described members of the family, being expressed in petals, sepals and vegetative apices, in addition to stigmas and anthers. Moreover, use of SLR3-derived probes in RNA blot and RACE-PCR (rapid amplification of cDNA ends-polymerase chain reaction) experiments has identified transcripts of genes closely related to SLR3 in leaves, cotyledons and, at high levels in developing anthers. SLR3 is not linked to the S locus but is linked to two or three closely related genes. Sequence analysis of the SLR3 gene indicates that it is derived from an ancestral receptor kinase gene that has been modified by a series of deletion events. As a result of these modifications, SLR3 is predicted to encode a secreted glycoprotein lacking both transmembrane and kinase domains. The putative SLR3 protein differs from the products of most other S gene family members in that several of the highly conserved cysteines have been lost. Within the S gene family, modification of receptor kinase genes by deletion may represent a general mechanism for the generation of genes encoding secreted glycoproteins.