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
Jiang H, Moreno-Romero J, Santos-González J, De Jaeger G, Gevaert K, Van De Slijke E, Köhler C (2017) Ectopic application of the repressive histone modification H3K9me2 establishes postzygotic reproductive isolation in Arabidopsis thaliana. Genes and Dev., 31: 1272-1284. (PubMed)
Lafon-Placette C, Johannessen IM, Hornslien KS, Ali MF, Bjerkan KN, Bramsiepe J, Glöckle BM, Rebernig CA, Brysting AK, Grini PE, Köhler C. (2017) Endosperm-based hybridization barriers explain the pattern of gene flow between Arabidopsis lyrata and Arabidopsis arenosa in Central Europe. PNAS, 114: E1027-E1035. (PubMed)
Figueiredo DD, Batista RA, Roszak PJ, Hennig, L, Köhler C. (2016) Auxin production in the endosperm drives seed coat development in Arabidopsis. eLIFE, e20542. (PubMed)
Hatorangan MR, Laenen B, Steige K, Slotte T, Köhler C. (2016) Rapid Evolution of Genomic Imprinting in Two Species of the Brassicaceae. Plant Cell. 28:1815-27. (PubMed)
Moreno-Romero J, Jiang H, Santos-González J, Köhler C (2016) Parental epigenetic asymmetry of PRC2-mediated histone modifications in the Arabidopsis endosperm. EMBO J. e201593534. (PubMed)
Martínez G, Panda K, Köhler C, Slotkin RK (2016) Silencing in sperm cells is directed by RNA movement from the surrounding nurse cell. Nature Plants 2: 16030 (PubMed)
Figueiredo DD, Batista RA, Roszak PJ, Köhler C (2015) Auxin production couples endosperm development to fertilization. Nature Plants: 15184 (PubMed)
Wolff P, Jiang H, Wang G, Santos-Gonzàlez J, Köhler C (2015) Paternally expressed imprinted genes establish postzygotic hybridization barriers in Arabidopsis thaliana. eLife1 0.7554 (PubMed)
Rebernig CA, Lafon-Placette C, Hatorangan MR, Slotte T, Köhler C (2015) Non-reciprocal Interspecies Hybridization Barriers in the Capsella Genus are Established in the Endosperm. PLoS Genet. 11(6).(PubMed)
Brownfield L, Yi J, Jiang H, Minina EA, Twell D, Köhler C (2015) Organelles maintain spindle position in plant meiosis. Nature Comm. 6: 6492. (PubMed)
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. (PubMed)
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. (PubMed)
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. (PubMed)
Hehenberger E, Kradolfer D, Köhler C (2012) Endosperm cellularization defines an important developmental transition for embryo development. Development, 139: 2031-203 (PubMed)
Roszak P, Köhler C (2011) Polycomb group proteins are required to couple seed coat initiation to fertilization (2011) Proceedings of the National Academy of Sciences of the USA 108:20826-31 (PubMed)