Genomic Imprinting in the Endosperm Is Systematically Perturbed in Abortive Hybrid Tomato Seeds.
Hybrid seed failure represents an important postzygotic barrier to interbreeding among species of wild tomatoes (Solanum section Lycopersicon) and other flowering plants. We studied genome-wide changes associated with hybrid seed abortion in the closely related Solanum peruvianum and S. chilense where hybrid crosses yield high proportions of inviable seeds due to endosperm failure and arrested embryo development. Based on differences of seed size in reciprocal hybrid crosses and developmental evidence implicating endosperm failure, we hypothesized that perturbed genomic imprinting is involved in this strong postzygotic barrier. Consequently, we surveyed the transcriptomes of developing endosperms from intra- and inter-specific crosses using tissues isolated by laser-assisted microdissection. We implemented a novel approach to estimate parent-of-origin-specific expression using both homozygous and heterozygous nucleotide differences between parental individuals and identified candidate imprinted genes. Importantly, we uncovered systematic shifts of "normal" (intraspecific) maternal:paternal transcript proportions in hybrid endosperms; the average maternal proportion of gene expression increased in both crossing directions but was stronger with S. peruvianum in the maternal role. These genome-wide shifts almost entirely eliminated paternally expressed imprinted genes in S. peruvianum hybrid endosperm but also affected maternally expressed imprinted genes and all other assessed genes. These profound, systematic changes in parental expression proportions suggest that core processes of transcriptional regulation are functionally compromised in hybrid endosperm and contribute to hybrid seed failure.
Plant Ecological Genetics, Institute of Integrative Biology & Zurich-Basel Plant Science Center, ETH Zurich, Zurich, Switzerland.
Ana M
AM
Florez-Rueda
Plant Ecological Genetics, Institute of Integrative Biology & Zurich-Basel Plant Science Center, ETH Zurich, Zurich, Switzerland.
Margot
M
Paris
Plant Developmental Genetics, Department of Plant and Microbial Biology & Zurich-Basel Plant Science Center, University of Zurich, Zurich, Switzerland.
Anja
A
Schmidt
Plant Ecological Genetics, Institute of Integrative Biology & Zurich-Basel Plant Science Center, ETH Zurich, Zurich, Switzerland.
Alex
A
Widmer
Plant Developmental Genetics, Department of Plant and Microbial Biology & Zurich-Basel Plant Science Center, University of Zurich, Zurich, Switzerland.
Ueli
U
Grossniklaus
Plant Ecological Genetics, Institute of Integrative Biology & Zurich-Basel Plant Science Center, ETH Zurich, Zurich, Switzerland thomas.staedler@env.ethz.ch.
Thomas
T
Städler
D000483:Alleles; D002678:Chimera; D019175:DNA Methylation; D056625:Endosperm / Q000235:genetics* / Q000378:metabolism; D020869:Gene Expression Profiling / Q000379:methods; D017343:Genes, Plant; D018745:Genome, Plant; D018392:Genomic Imprinting; D018551:Solanum lycopersicum / Q000235:genetics*; D059467:Transcriptome
Solanum; endosperm; genomic imprinting; postzygotic isolation; seed failure