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Mechanisms and control of reproductive development in plants

English title Mechanisms and control of reproductive development in plants
Applicant Köhler Claudia
Number 123362
Funding scheme SNSF Professorships
Research institution Departement Umweltsystemwissenschaften ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Botany
Start/End 01.07.2009 - 30.06.2011
Approved amount 745'416.00
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All Disciplines (4)

Discipline
Botany
Genetics
Embryology, Developmental Biology
Molecular Biology

Keywords (6)

seed development; Arabidopsis thaliana; genetics; epigenetics; Polycomb group proteins; FERTILIZATION INDEPENDENT SEED mutants

Lay Summary (English)

Lead
Lay summary
In flowering plants, seed development begins with the fertilization of the egg cell and the central cell by the male gametes, giving rise to the diploid embryo and the triploid endosperm, respectively. Although the genome information present in the embryo and the endosperm is identical, the fate of both fertilization products is extremely different. Embryo and endosperm development occur coordinated and influence each other. Mutants of the fertilization independent seed (FIS) class have defects in the coordinated development of embryo and endosperm. In FIS mutants endosperm development can initiate in the absence of a fertilization signal. If fertilization occurs, the endosperm proliferates abnormally and the embryo aborts. The FIS genes encode for Polycomb group (PcG) proteins, a class of proteins that ensure the mitotically stable repression of their target genes. We could show that FIS proteins assemble into a large molecular weight complex (FIS complex) and that this complex has histone methyltransferase activity targeting specifically histone H3 lysine 27. The major goal of the proposed projects is to gain a better understanding of seed development and the impact of epigenetic regulatory processes on seed development. Seeds are our main food source, thus besides of a substantial scientific impact the investigation of seed development also has a great economical impact. To reach our main goal we plan i) to elucidate the mechanism of FIS mediated gene repression in plants, ii) to elucidate the functional role of the FIS PcG complex in the central cell and during seed development, and iii) to elucidate the imprinting mechanism of the PcG target gene PHE1. PcG complexes are conserved in animals and plants; therefore, we expect that the result of these studies will be of general interest for the scientific community.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

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Associated projects

Number Title Start Funding scheme
106684 Mechanisms and control of reproductive development in plants 01.07.2005 SNSF Professorships

Abstract

BackgroundIn flowering plants, seed development begins with the fertilization of the egg cell and the central cell by the male gametes, giving rise to the diploid embryo and the triploid endosperm, respectively. Although the genome information present in the embryo and the endosperm is identical, the fate of both fertilization products is extremely different. Embryo and endosperm development occur coordinated and influence each other. Mutants of the fertilization independent seed (fis) class have defects in the coordinated development of embryo and endosperm. In fis mutants endosperm development can initiate in the absence of a fertilization signal. If fertilization occurs, the endosperm proliferates abnormally and the embryo aborts. The FIS genes encode forPolycomb group (PcG) proteins, a class of proteins that ensure the mitotically stable repression of their target genes. We could show that FIS proteins assemble into a large molecular weight complex (FIS complex) and that this complex has histone methyltransferase activity targeting specifically histone H3 lysine 27. Working hypotheses and specific research aims(i)How PcG mediate silencing of their target genes is mechanistically not understood. Based on results obtained from a mutant screen we propose that PcG proteins act together with proteins of the RNA interference (RNAi) pathway to mediate long range interactions of Polycomb response elements (PREs) causing stable silencing of PcG target genes. We will test this hypothesis by analyzing whether indeed PREs pair with each other and whether pairing depends on the presence of PcG proteins and proteins of the RNAi machinery.(ii)Mutations in FIS genes cause parent-of-origin dependent seed abortion. All seeds that inherit a mutant fis allele from the mother abort, regardless of the presence of a wild-type paternal allele. Development of fis mutant seeds is delayed, and seeds abort with embryos arrested at late heart stage and non-cellularized endosperm with strongly overproliferated chalazal endosperm domains. The underling cause for embryo arrest and seed abortion in fis mutant seeds is unknown. Based on initial results we hypothesize that fis mutant endosperm is not providing the necessary nutrients or appropriate nutrient concentrations to embryos surrounded by mutant endosperm, resulting in growth arrest. We will test this hypothesis by comparing the metabolite status of fis mutant seeds with wild-type seeds. Furthermore, we will search for new target genes of the FIS complex using a suppressor screen of the fis seed abortion phenotype.(iii)Mutations in FIS genes cause autonomous endosperm development, suggesting that the FIS complex suppresses autonomous proliferation of the central cell nucleus. To gain insights into this mechanism we have searched for suppressor mutants of this phenotype. We have identified two mutants that we plan to characterize in detail.(iv)The type I MADS-box gene PHERES1 (PHE1) is a direct target gene of the FIS PcG complex. PHE1 the only plant gene known to be paternally expressed and maternally silenced. Maternal PHE1 silencing is caused by the repressing activity of the FIS complex and requires a DNA methylated region downstream of the PHE1 locus. We hypothesize that PHE1 imprinting is associated with differential methylation of maternal and paternal PHE1 alleles. This hypothesis will be tested by determining the allele-specific methylation status of PHE1 in the Arabidopsis endosperm.(v)Parent-of-origin dependent gene expression in plants takes place only in the endosperm. This, together with the triploid nature of the endosperm makes it likely that in the endosperm regulation of gene expression differs compared to vegetative tissues. In a mutant screen we have searched for potential regulators of endosperm development. Based on initial results we hypothesize that increasing the paternal genome contribution causes upregulation of FIS target genes by limiting the number of available FIS PcG complexes. We will test this hypothesis by comparing the expression profile of triploid mutant seeds with the expression profile of fis mutant seeds and search for commonly deregulated genes.Expected value of the proposed projectsThe major goal of the proposed projects is to gain a better understanding of seed development and the impact of epigenetic regulatory processes on seed development. Seeds are our main food source, thus besides of a substantial scientific impact the investigation of seed development also has a great economical impact. To reach our main goal we plan i) to elucidate the mechanism of PcG mediated gene repression in plants, ii) to elucidate the functional role of the FIS PcG complex in the central cell and during seed development, iii) to elucidate the functional requirement of the FIS PcG complex during polyploidization, and iv) to elucidate the imprinting mechanism of the PcG target gene PHE1. PcG complexes are conserved in animals and plants; therefore, we expect that the result of these studies will be of general interest for the scientific community.
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