Apomixis in agriculture: the quest for clonal seeds

Apomixis, or asexual reproduction through seeds, is a natural trait that could have an immense positive impact on crop production. Apomictic breeding strategies could allow the fixation and indefinite propagation of any desired genotype, however complex. Apomicts display a wide variety of developmental mechanisms, which can be viewed as a short-circuiting of sexual development. Gametophytic and sporophytic apomixis are distinguished by the developmental origin of apomictically derived embryos. Genetic studies suggest that individual elements of gametophytic apomixis, such as apomeiosis and parthenogenesis, are either controlled by one or two dominant Mendelian factors. As recombination around apomeiosis loci is suppressed, it is currently not known how complex these loci are. Much less is known regarding the genetic control of sporophytic apomixis but initial studies suggest a complex genetic control. Genetic analyses of sexual reproduction in plant model systems have identified genes that, when mutated, display elements of apomixis. Such studies help in the identification of candidate genes and promoters that can be used for the de novo engineering of apomixis through biotechnology. Molecular genetic studies in apomictic and sexual systems will generate the knowledge necessary for the engineering of conditional apomixis technology. Approaches encouraging collaboration and widespread dissemination of the acquired knowledge will constitute the most innovative route to the development, deployment and acceptance of apomixis technology in agriculture.     

Dimerization of Receptor Protein-Tyrosine Phosphatase alpha in living cells

Background  

Dimerization is an important regulatory mechanism of single membrane-spanning receptors. For instance, activation of receptor protein-tyrosine kinases (RPTKs) involves dimerization. Structural, functional and biochemical studies suggested that the enzymatic counterparts of RPTKs, the receptor protein-tyrosine phosphatases (RPTPs), are inhibited by dimerization, but whether RPTPs actually dimerize in living cells remained to be determined.     

"Rheumatoid Arthritis": A balanced overview of current research

This is a brief review of the third volume of the series edited by AN Theofilopoulos, "Current Directions in Autoimmunity". This hard-cover volume comprises 282 pages, 46 figures and 14 tables. The book has a cover price of 196 Swiss Francs, or 255 Deutschmarks, or 170.50 US dollars.     

Application of the U and gamma' models in binary sweet taste mixtures

The U and Gamma' models of sensory interactions, successfully applied in olfaction for several years, are tested here using data from published studies on sweetness. The models are subsequently tested on new data obtained in studies of binary mixtures of four sodium sulfamates. The U model allows for the estimation of a global interaction, whereas the Gamma' model allows for the distinction between that which is due to an intrinsic interaction in the mixture itself and that which may be due to the power function exponents in the mixture. The models give satisfactory predictions for observed phenomena of sweet taste suppression, synergism or pure additivity. Additionally, they appear to be more suitable than other models recently applied in taste, particularly the equiratio model. Application of the models to the sulfamate mixtures, reveals additivity for sodium cyclohexylsulfamate (cyclamate)/potassium cyclohexylsulfamate and sodium cyclohexylsulfamate/sodium exo-2-norbornylsulfamate, respectively; whereas for sodium cyclohexylsulfamate/sodium 3-bromophenylsulfamate, the models revealed a slight hypo addition which is simply due to the dissimilarity values of the power function exponents of the components.     

Evolutionary origins of the endosperm in flowering plants

The evolutionary origin of double fertilization and the resultant endosperm tissue in flowering plants remains a puzzle, despite over a century of research. The recent resurgence of approaches to evolutionary developmental biology combining comparative biology with phylogenetics provides new understanding of endosperm origins.     

Apomixis technology development-virgin births in farmers' fields?

Apomixis is the process of asexual reproduction through seed, in the absence of meiosis and fertilization, generating clonal progeny of maternal origin. Major benefits to agriculture could result from harnessing apomixis in crop plants. Although >400 apomictic plant species are known, apomixis is rare among crop plants, and the transfer of apomixis to crop varieties by conventional breeding has been largely unsuccessful. Because apomictic and sexual pathways are closely related, de novo engineering of apomixis might be achieved in sexually reproducing crops. Early consideration of issues relating to biosafety and intellectual property (IP) management can facilitate the acceptance and deployment of apomixis technology in agriculture.     

Differentiation of naive CD4<Superscript>+</Superscript> T cells towards T helper 2 cells is not impaired in rheumatoid arthritis patients

An impaired differentiation of naive CD4+ T cells towards Th2 cells may contribute to the chronic tissue-destructive T-cell activity in rheumatoid arthritis (RA). The differentiation of naive CD4+ T cells into memory Th2 cells by IL-7 in comparison with that by IL-4 was studied in RA patients and in healthy controls. Naive CD4+ T cells from peripheral blood were differentiated by CD3/CD28 costimulation in the absence of or in the presence of IL-7 and/or IL-4. The production of IFN-gamma and IL-4 was measured by ELISA and by single-cell FACS analysis to indicate Th1 and Th2 cell activity. CD3/CD28 costimulation and IL-7 were early inducers of IL-4 production, but primarily stimulated IFN-gamma production. In contrast, in short-term cultures exogenously added IL-4 did not prime for IL-4 production but suppressed IL-7-induced IFN-gamma production. Upon long-term stimulation of naive CD4+ T cells, IFN-gamma production was differentially regulated by IL-7 and IL-4, but IL-4 production was increased by both IL-7 and IL-4. IL-7 and IL-4 additively induced polarization towards a Th2 phenotype. This susceptibility of naive CD4+ T cells to become Th2 cells upon culture with IL-7 and IL-4 was increased in RA patients compared with that in healthy controls. These findings demonstrate that, in RA patients, differentiation of naive CD4+ T cells towards a Th2 phenotype by CD3/CD28 costimulation, IL-7 and IL-4 is not impaired. The perpetuation of arthritogenic T-cell activity in RA therefore seems not to be the result of intrinsic defects of naive CD4+ T cells to develop towards suppressive memory Th2 cells.     

Abatacept decreases disease activity in a absence of CD4+ T cells in a collagen-induced arthritis model

IntroductionAbatacept is a fusion protein of human cytotoxic T-lymphocyte–associated protein (CTLA)-4 and the Fc portion of human immunoglobulin G1 (IgG1). It is believed to be effective in the treatment of rheumatoid arthritis by inhibiting costimulation of T cells via blocking CD28–B7 interactions as CTLA-4 binds to both B7.1 (CD80) and B7.2 (CD86). However, the interaction of CD28 with B7 molecules is crucial for activation of naive cells, whereas it is unclear whether the action of already activated CD4⁺ T cells, which are readily present in established disease, also depends on this interaction. The aim of this study was to determine whether the mode of action of abatacept depends solely on its ability to halt T cell activation in established disease.MethodsArthritis was induced in thymectomized male DBA/1 mice by immunisation with bovine collagen type II. The mice were subsequently depleted for CD4⁺ T cells. Abatacept or control treatment was started when 80 % of the mice showed signs of arthritis. Arthritis severity was monitored by clinical scoring of the paws, and anti-collagen antibody levels over time were determined by enzyme-linked immunosorbent assay.ResultsTreatment with abatacept in the absence of CD4⁺ T cells resulted in lower disease activity. This was associated with decreasing levels of collagen-specific IgG1 and IgG2a antibodies, whereas the antibody levels in control or CD4⁺ T cell–depleted mice increased over time.ConclusionsThese results show that abatacept decreased disease activity in the absence of CD4⁺ T cells, indicating that the mode of action of abatacept in established arthritis does not depend entirely on its effects on CD4⁺ T cell activation.