The evolution of seeds is one of the most dramatic innovations during land plant evolution and contributed to the evolutionary success of angiosperms. A seed consists of an embryo surrounded by the endosperm and a maternally derived seed coat. The endosperm of many crop species like maize, rice and wheat is the major source of human nutrition and animal feed, therefore, unraveling the processes governing endosperm development is of crucial importance. The endosperm is essential for embryo development and a major determinant for seed growth. One aim of our lab is to identify the genetic basis for endosperm-mediated seed size control in plants. The endosperm is as well a major barrier to interspecies and interploidy hybridizations. We aim at identifying the underlying genetic basis for this phenomenon.
Functional Requirement of the Endosperm for Seed Development. Seed development depends on a functional endosperm, however, the functional role of the endosperm for embryo and seed development is still poorly understood. We aim at elucidating which developmental steps of the endosperm are essential for embryo development and which genetic pathways are responsible for endosperm-mediated seed growth.
Expression of an endosperm marker gene during seed development.
Polyploidy-Mediated Plant Speciation. Polyploidization is a widespread phenomenon among plants and is considered a major speciation mechanism. Polyploids have a high degree of immediate post-zygotic reproductive isolation from their progenitors, as backcrossing to either parent will produce mainly nonviable progeny. This reproductive barrier is called triploid block and is caused by malfunction of the endosperm. Until recently, neither the formation of unreduced gametes nor the triploid block were understood mechanistically. We have shown that in response to interploidy crosses target genes of chromatin-modifying Polycomb group complexes are deregulated on a genome-wide scale, implicating loss of Polycomb group function being responsible for establishing the triploid block. The aim of this project is to identify the genetic basis of the triploid block in plants.
Genomic Imprinting in the Endosperm.Genomic imprinting is an epigenetic phenomenon causing parent-of-origin-specific gene expression of genetically identical alleles. Genomic imprinting has evolved only in mammals and flowering plants and it has been hypothesized that the function of genomic imprinting and imprinted genes is to regulate the nutrient transfer from the mother to the offspring. Consequently, imprinted genes should be seed size regulators. We have identified genes regulated by genomic imprinting on a genome-wide scale and currently analyze the functional requirement of these genes during seed development.
To the left: Increased expression of the Polycomb group target gene PHERES1 in triploid seeds. To the right: Abnormal development of triploid seeds formed by the jason mutant
Brownfield L, Yi J, Jiang H, Minina EA, Twell D, Köhler C (2015) Organelles maintain spindle position in plant meiosis. Nature Comm., in press.
Schatlowski N, Wolff P, Santos-González J, Schoft V, Siretskiy A, Scott R, Tamaru H, Köhler C (2014) Hypomethylated Pollen Bypasses the Interploidy Hybridization Barrier in Arabidopsis. Plant Cell,26:3556-68.
Kradolfer D, Wolff P, Jiang H, Siretskiy A, Köhler C. (2013) An imprinted gene underlies postzygotic reproductive isolation in Arabidopsis thaliana. Dev Cell. 26: 525-35.
Kradolfer D, Hennig H, Köhler C (2013) Increased maternal genome dosage bypasses the requirement of the FIS Polycomb Repressive Complex 2 in Arabidopsis seed development. PLoS Genet. 9: e1003163.
Hehenberger E, Kradolfer D, Köhler C (2012) Endosperm cellularization defines an important developmental transition for embryo development. Development, 139: 2031-203
Aichinger, E., Villar, C.B., Di Mambro, R., Sabatini, S., Köhler, C. (2011) The CHD3 Chromatin Remodeler PICKLE and Polycomb Group Proteins Antagonistically Regulate Meristem Activity in the Arabidopsis Root. Plant Cell, 23:1047-1060.
Wolff P, Weinhofer I, Seguin J, Roszak P, Beisel C, Donoghue MT, Spillane C, Nordborg M, Rehmsmeier M, Köhler C. (2011) High-Resolution Analysis of Parent-of-Origin Allelic Expression in the Arabidopsis Endosperm. PLoS Genet. 6:e1002126.
Weinhofer, I., Hehenberger, E., Roszak, P., Hennig, L., Köhler, C. (2010) H3K27me3 Profiling of the Endosperm Implies Exclusion of Polycomb group Protein Targeting by DNA Methylation. PLoS Genet 6: e1001152. (PubMed)
Erilova, E., Brownfield, L., Exner, V., Rosa, M., Twell, D., Mittelsten Scheid, O., Hennig, L., Köhler, C. (2009) Imprinting of the Polycomb Group Gene MEDEA Serves as a Ploidy Sensor in Arabidopsis. PLoS Genet. 5:e1000663. (PubMed)
Aichinger, E., Villar, C.B.R., Farrona, S., Reyes, J.C., Hennig, L., Köhler, C. (2009) CHD3 proteins and Polycomb group proteins antagonistically determine cell identity in Arabidopsis. PLoS Genet. (8):e1000605. (PubMed)